4,957 research outputs found
Generalised Kundt waves and their physical interpretation
We present the complete family of space-times with a non-expanding,
shear-free, twist-free, geodesic principal null congruence (Kundt waves) that
are of algebraic type III and for which the cosmological constant ()
is non-zero. The possible presence of an aligned pure radiation field is also
assumed. These space-times generalise the known vacuum solutions of type N with
arbitrary and type III with . It is shown that there
are two, one and three distinct classes of solutions when is
respectively zero, positive and negative. The wave surfaces are plane,
spherical or hyperboloidal in Minkowski, de Sitter or anti-de Sitter
backgrounds respectively, and the structure of the family of wave surfaces in
the background space-time is described. The weak singularities which occur in
these space-times are interpreted in terms of envelopes of the wave surfaces.Comment: 16 pages including 2 figures. To appear in Classical and Quantum Gra
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Evolution of political branding: typologies, diverse settings and future research
Political branding has developed into an established and vibrant sub-discipline of political marketing. Indeed, political branding research continues to push boundaries by critically applying consumer based branding theories, concepts and frameworks to the political environment. Recently, political branding scholars have segmented research into different categories such as corporate, candidate, leader, local-regional, internal or external in orientation. Despite this development, there continues to be limited research on alternative or different typologies of political brands. This study reaffirms political branding as a distinct area of research and discusses how political brands can be conceptualised and operationalised. Further, drawing on seven empirical and conceptual papers, which focus on different typologies of political brands from a range of international contexts including Canada, USA, Iceland, Indonesia and India, we reflect on the current political branding environment. We conclude that there are multiple relationships and numerous interconnected political brands, which represent an intricate environment or ecosystem. This study offers academics and political actors guidance on how to conceptualise political brands and provides a starting point to map out the ecosystems of political brands. Finally, this study provides explicit calls for further research in political branding
Helicopter tail rotor orthogonal blade vortex interaction
The aerodynamic operating environment of the helicopter is particularly complex and,
to some extent, dominated by the vortices trailed from the main and tail rotors. These
vortices not only determine the form of the induced flow field but also interact with
each other and with elements of the physical structure of the flight vehicle. Such
interactions can have implications in terms of structural vibration, noise generation
and flight performance. In this paper, the interaction of main rotor vortices with the
helicopter tail rotor is considered and, in particular, the limiting case of the orthogonal
interaction. The significance of the topic is introduced by highlighting the operational
issues for helicopters arising from tail rotor interactions. The basic phenomenon is
then described before experimental studies of the interaction are presented. Progress
in numerical modelling is then considered and, finally, the prospects for future
research in the area are discussed
Giving voters what they want? Party orientation perceptions and preferences in the British electorate
Some of the most important propositions in the political marketing literature hinge on assumptions about the electorate. In particular, voters are presumed to react in different ways to different orientations or postures. Yet there are theoretical reasons for questioning some of these assumptions, and certainly they have seldom been empirically tested. Here, we focus on one prominent example of political marketing research: Lees-Marshment’s orientations’ model. We investigate how the public reacts to product and market orientation, whether they see a trade-off between the two (a point in dispute among political marketing scholars), and whether partisans differ from non-partisan voters by being more inclined to value product over market orientation. Evidence from two mass sample surveys of the British public (both conducted online by YouGov) demonstrates important heterogeneity within the electorate, casts doubt on the core assumptions underlying some political marketing arguments and raises broader questions about what voters are looking for in a party
Synchronization in complex networks
Synchronization processes in populations of locally interacting elements are
in the focus of intense research in physical, biological, chemical,
technological and social systems. The many efforts devoted to understand
synchronization phenomena in natural systems take now advantage of the recent
theory of complex networks. In this review, we report the advances in the
comprehension of synchronization phenomena when oscillating elements are
constrained to interact in a complex network topology. We also overview the new
emergent features coming out from the interplay between the structure and the
function of the underlying pattern of connections. Extensive numerical work as
well as analytical approaches to the problem are presented. Finally, we review
several applications of synchronization in complex networks to different
disciplines: biological systems and neuroscience, engineering and computer
science, and economy and social sciences.Comment: Final version published in Physics Reports. More information
available at http://synchronets.googlepages.com
Holographic Anomalous Conductivities and the Chiral Magnetic Effect
We calculate anomaly induced conductivities from a holographic gauge theory
model using Kubo formulas, making a clear conceptual distinction between
thermodynamic state variables such as chemical potentials and external
background fields. This allows us to pinpoint ambiguities in previous
holographic calculations of the chiral magnetic conductivity. We also calculate
the corresponding anomalous current three-point functions in special kinematic
regimes. We compare the holographic results to weak coupling calculations using
both dimensional regularization and cutoff regularization. In order to
reproduce the weak coupling results it is necessary to allow for singular
holographic gauge field configurations when a chiral chemical potential is
introduced for a chiral charge defined through a gauge invariant but
non-conserved chiral density. We argue that this is appropriate for actually
addressing charge separation due to the chiral magnetic effect.Comment: 17 pages, 1 figure. v2: 18 pages, 1 figure, discussion clarified
throughout the text, references added, version accepted for publication in
JHE
Stable stochastic dynamics in yeast cell cycle
Chemical reactions in cell are subject to intense stochastic fluctuations. An
important question is how the fundamental physiological behavior of cell is
kept stable against those noisy perturbations. In this paper a stochastic model
of cell cycle of budding yeast is constructed to analyze the effects of noise
on the cell cycle oscillation. The model predicts intense noise in levels of
mRNAs and proteins, and the simulated protein levels explain the observed
statistical tendency of noise in populations of synchronous and asynchronous
cells. In spite of intense noise in levels of proteins and mRNAs, cell cycle is
stable enough to bring the largely perturbed cells back to the physiological
cyclic oscillation. The model shows that consecutively appearing fixed points
are the origin of this stability of cell cycle.Comment: main text, 2 supporting texts, 3 supplementary table
Effect of alkyl chain length on the properties of triphenylamine-based hole transport materials and their performance in perovskite solar cells
A new series of diacetylide-triphenylamine (DATPA) derivatives with five different alkyl chains in the para position, MeO, EtO, nPrO, iPrO and BuO, were synthesised, fully characterised and their function as hole-transport materials in perovskite solar cells (PSC) studied. Their thermal, optical and electrochemical properties were investigated along with their molecular packing and charge transport properties to analyse the influence of different alkyl chains in the solar cell parameters. The shorter alkyl chain facilitates more compact packing structures which enhanced the hole mobilities and reduced recombination. This work suggests that the molecule with the methoxy substituent (MeO) exhibits the best semiconductive properties with a power conversion efficiency of up to 5.63%, an open circuit voltage (Voc) of 0.83 V, a photocurrent density (Jsc) of 10.84 mA cm−2 and a fill factor of 62.3% in perovskite solar cells. Upon replacing the methoxy group with longer alkyl chain substituents without changing the energy levels, there is a decrease in the charge mobility as well as PCE (e.g. 3.29% for BuO-DATPA). The alkyl chain length of semiconductive molecules plays an important role in achieving high performance perovskite solar cells
The DSF family of quorum sensing signals: diversity, biosynthesis, and turnover
The diffusible signaling factor (DSF)-based quorum sensing (QS) system has emerged as a widely conserved cell–cell communication mechanism in Gram-negative bacteria. Typically, signals from the DSF family are cis-2-unsaturated fatty acids which regulate diverse biological functions. Recently, substantial progress has been made on the characterization of new members of this family of signals. There have also been new developments in the understanding of the biosynthesis of these molecules where dual enzymatic activities of the DSF synthase and the use of various substrates have been described. The recent discovery of a naturally occurring DSF turnover mechanism and its regulation provides a new dimension in our understanding of how DSF-dependent microorganisms modulate virulence gene expression in response to changes in the surrounding environment
Interactive, multiscale navigation of large and complicated biological networks
Motivation: Many types of omics data are compiled as lists of connections between elements and visualized as networks or graphs where the nodes and edges correspond to the elements and the connections, respectively. However, these networks often appear as ‘hair-balls’—with a large number of extremely tangled edges—and cannot be visually interpreted
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