Field Theory Approaches to Nonequilibrium Dynamics

It is explained how field-theoretic methods and the dynamic renormalisation group (RG) can be applied to study the universal scaling properties of systems that either undergo a continuous phase transition or display generic scale invariance, both near and far from thermal equilibrium. Part 1 introduces the response functional field theory representation of (nonlinear) Langevin equations. The RG is employed to compute the scaling exponents for several universality classes governing the critical dynamics near second-order phase transitions in equilibrium. The effects of reversible mode-coupling terms, quenching from random initial conditions to the critical point, and violating the detailed balance constraints are briefly discussed. It is shown how the same formalism can be applied to nonequilibrium systems such as driven diffusive lattice gases. Part 2 describes how the master equation for stochastic particle reaction processes can be mapped onto a field theory action. The RG is then used to analyse simple diffusion-limited annihilation reactions as well as generic continuous transitions from active to inactive, absorbing states, which are characterised by the power laws of (critical) directed percolation. Certain other important universality classes are mentioned, and some open issues are listed.Comment: 54 pages, 9 figures, Lecture Notes for Luxembourg Summer School "Ageing and the Glass Transition", submitted to Springer Lecture Notes in Physics (www.springeronline/com/series/5304/

Multi-color Optical Variability of the TeV Blazar Mrk 501 in the Low-State

We report results based on the monitoring of the BL Lac object Mrk 501 in the optical (B, V and R) passbands from March to May 2000. Observations spread over 12 nights were carried out using 1.2 meter Mount Abu Telescope, India and 61 cm Telescope at Sobaeksan Astronomy Observatory, South Korea. The aim is to study the intra-day variability (IDV), short term variability and color variability in the low state of the source. We have detected flux variation of 0.05 mag in the R-band in time scale of 15 min in one night. In the B and V passbands, we have less data points and it is difficult to infer any IDVs. Short term flux variations are also observed in the V and R bands during the observing run. No significant variation in color (B$-$R) has been detected but (V$-$R) shows variation during the present observing run. Assuming the shortest observed time scale of variability (15 min) to represent the disk instability or pulsation at a distance of 5 Schwarschild radii from the black hole (BH), mass of the central BH is estimated $\sim$ 1.20 $\times$ 10$^{8} M_{\odot}$.Comment: 4 figures, 4 tables, Accepted for publication in New Astronom

The Persistency of the India-Pakistan Conflict: Chances and Obstacles of the Bilateral Composite Dialogue

This article investigates the underlying causes for the persistency of the India–Pakistan conflict and, on this basis, the chances and obstacles of the bilateral composite dialogue initiated in 2004. In particular, it wants to provide a theoretically grounded account of the factors that facilitated and constrained the bilateral composite dialogue process. Drawing on the regional security complex theory, this article examines the rivalry between the two South Asian nuclear powers on four levels of analysis: the domestic, the regional, the interregional and the global level. The analysis shows that there have been some substantial changes on all four levels in the recent decade or so and that these changes have provided more beneficial conditions for a peace process. These changes include, inter alia, India’s new regional policy, the consequences of the 9/11 terrorist attacks for the region and India’s growing power capacities. However, major obstacles to the India–Pakistan dialogue and a permanent conflict resolution continue to persist: the dominant role of the military in Pakistan, conflicting national identities and the still partially contested nature of statehood in India and Pakistan, which is in the case of Pakistan linked to the growing power of Islamic fundamentalists

A direct Navier-Stockes solver for turbulent flows over round steps

Direct Numerical Simulations (DNS) provide an increasing data source to improve our understanding of turbulent flows. Such DNS are especially required (together with generic experiments) to support flow physical modeling od separated, two- and three-dimensional vortex flows. In perspective to improve the prediction of such flows (either by new turbulence models or Large Eddy Simulations (LES) data fields are required which resolve turbulence and unsteady separated flow features. This is still a challenging task. However, a fully conservative, second order accurate, boundary correction method for Cartesian grids has been developed and implemented in an existing direct Navier-Stokes (NS) solver. For the case of a round backward facing channel step, laminar flow results generated with the proposed method agree well with those calculated on curvilinear, colocated grids. A Direct Numerical Simulation (DNS) of the turbulent flow in a minimal channel domain is performed for a Reynolds number based on friction velocity and channel height of ReT=265 for an efficiency analysis. Additionally the turbulent flows in a channel and a round backward facing channel step are calculated by means of DNS. The former simulation provides inflow conditions for the latter. The upstream Reynolds is ReT=360. Good agreement is obtained comparing statistically averaged variables of the turbulent channel flow with those of Kim et al. [3]. A mean recirculation zone, with mean separation/reattachment points being located 2.0/7.5 step heights downstream the step entrance, is computed in the DNS through the round backward facing channel step. Instantaneous and statistical flow variables are presented. They give an impression of the complex flow dynamics in the free shear layer, the recirculation and reattachment region

Adaptive plasticity of bushcricket acoustic signalling in socially heterogeneous choruses

Anichini M, Rebrina F, Reinhold K, Lehmann GUC. Adaptive plasticity of bushcricket acoustic signalling in socially heterogeneous choruses. ANIMAL BEHAVIOUR. 2019;158:139-148.In many species, males produce sounds to attract a female. In a chorus, males actively adjust their acoustic production depending on the presence and number of mating rivals. Plasticity in signal features might then be advantageous as males could tune their signalling activity to the contest intensity. However, the ability to exhibit plastic behaviour might be constrained and interindividual variation in plasticity can occur. In this field study, we examined the influence of body mass and social environment on the signal expression of male bushcrickets, Poecilimon veluchianus veluchianus. We tested whether differences in signal features of rivals of different body mass and number led to changes in the competition pressure perceived by focal males and, consequently, in their acoustic responses. We used the first principal component from a principal component analysis, reflecting verse duration, duty cycle and syllable number, as a measure of acoustic output. We found that the rivals' acoustic output depended only on their number, being higher for two rivals than one. However, the response of heavy focal males depended on the rivals' body mass. Contrary to what we expected, heavy males produced shorter verses with fewer syllables when competing against two heavy rivals than when competing against one or two light rivals or one heavy rival. Facing light competitors, heavy focal males responded more to two rivals than to one. In contrast, light focal males did not vary their signal features depending on competition conditions. These results indicate that body mass and social context drive interindividual variation in the capacity of P. v. veluchianus males to adjust their signal features to competition levels. We compare these findings with those previously obtained on congeneric species and discuss the outcomes' similarities and discrepancies. Lastly, we provide suggestions for future studies of socially induced plasticity in sexually selected acoustic signal features. (C) 2019 The Association for the Study of Animal Behaviour. Published by Elsevier Ltd. All rights reserved

A framework for advancing sustainable magnetic resonance imaging access in Africa

Magnetic resonance imaging (MRI) technology has profoundly transformed current healthcare systems globally, owing to advances in hardware and software research innovations. Despite these advances, MRI remains largely inaccessible to clinicians, patients, and researchers in low-resource areas, such as Africa. The rapidly growing burden of noncommunicable diseases in Africa underscores the importance of improving access to MRI equipment as well as training and research opportunities on the continent. The Consortium for Advancement of MRI Education and Research in Africa (CAMERA) is a network of African biomedical imaging experts and global partners, implementing novel strategies to advance MRI access and research in Africa. Upon its inception in 2019, CAMERA sets out to identify challenges to MRI usage and provide a framework for addressing MRI needs in the region. To this end, CAMERA conducted a needs assessment survey (NAS) and a series of symposia at international MRI society meetings over a 2-year period. The 68-question NAS was distributed to MRI users in Africa and was completed by 157 clinicians and scientists from across Sub-Saharan Africa (SSA). On average, the number of MRI scanners per million people remained at less than one, of which 39% were obsolete low-field systems but still in use to meet daily clinical needs. The feasibility of coupling stable energy supplies from various sources has contributed to the growing number of higher-field (1.5 T) MRI scanners in the region. However, these systems are underutilized, with only 8% of facilities reporting clinical scans of 15 or more patients per day, per scanner. The most frequently reported MRI scans were neurological and musculoskeletal. The CAMERA NAS combined with the World Health Organization and International Atomic Energy Agency data provides the most up-to-date data on MRI density in Africa and offers a unique insight into Africa's MRI needs. Reported gaps in training, maintenance, and research capacity indicate ongoing challenges in providing sustainable high-value MRI access in SSA. Findings from the NAS and focused discussions at international MRI society meetings provided the basis for the framework presented here for advancing MRI capacity in SSA. While these findings pertain to SSA, the framework provides a model for advancing imaging needs in other low-resource settings