Lyapunov instability of fluids composed of rigid diatomic molecules

We study the Lyapunov instability of a two-dimensional fluid composed of rigid diatomic molecules, with two interaction sites each, and interacting with a WCA site-site potential. We compute full spectra of Lyapunov exponents for such a molecular system. These exponents characterize the rate at which neighboring trajectories diverge or converge exponentially in phase space. Quam. These exponents characterize the rate at which neighboring trajectories diverge or converge exponentially in phase space. Qualitative different degrees of freedom -- such as rotation and translation -- affect the Lyapunov spectrum differently. We study this phenomenon by systematically varying the molecular shape and the density. We define and evaluate ``rotation numbers'' measuring the time averaged modulus of the angular velocities for vectors connecting perturbed satellite trajectories with an unperturbed reference trajectory in phase space. For reasons of comparison, various time correlation functions for translation and rotation are computed. The relative dynamics of perturbed trajectories is also studied in certain subspaces of the phase space associated with center-of-mass and orientational molecular motion.Comment: RevTeX 14 pages, 7 PostScript figures. Accepted for publication in Phys. Rev.

Covariant hydrodynamic Lyapunov modes and strong stochasticity threshold in Hamiltonian lattices

We scrutinize the reliability of covariant and Gram-Schmidt Lyapunov vectors for capturing hydrodynamic Lyapunov modes (HLMs) in one-dimensional Hamiltonian lattices. We show that,in contrast with previous claims, HLMs do exist for any energy density, so that strong chaos is not essential for the appearance of genuine (covariant) HLMs. In contrast, Gram-Schmidt Lyapunov vectors lead to misleading results concerning the existence of HLMs in the case of weak chaos.Comment: 4 pages, 4 figures. Accepted for publication in Physical Review

Visibly better? Testing the effect of ethnic appearance on citizen perceptions of the police

Ethnic minority officers continue to be underrepresented across UK police forces. Further, some ethnic minority groups consistently report lower levels of confidence in police compared to their White British counterparts. Although there is consensus that a more ethnically representative police service is a good idea, there is limited evidence in the UK on how the public perceives officers of different ethnic appearance, and how this relates to trust, confidence and legitimacy. This paper presents findings from an online experiment (n = 260) exploring how ethnic appearance affects perceptions of police. Our findings offer rare empirical support for a more ethnically representative police force. First, across respondents, we found that Black officers were perceived significantly more favourably than White or Asian officers. Second, we found that Black respondents had more negative responses to White officers, yet there was little evidence that Black officers elicited more negative reactions from White or Asian respondents. We discuss the theoretical and practical implications of the findings

The “hidden strength” of active citizenship: the involvement of local residents in public safety projects

The past two decades or so have seen a growing interest in 'active' (or 'responsible') citizenship within local public safety projects and programmes, but little is known about how such projects function in practice. Besides presenting theoretical debates on community safety projects, this article reports empirical insights into the wealth and variety of informal, citizen-based contributions, specifically to handling communal crime and disorder in Amsterdam, capital city of the Netherlands. Subsequently, it assesses the kind of lessons empirical studies provide about the importance of 'social capital' for public participation, the perils of social exclusion and the nature of relationships between citizens and professionals. It is argued that enthusiastic efforts of individual citizens are equally important, if not more so, than strong social ties. Moreover, in overall terms, active participation tends to have a significant bias in favour of the white, middle-aged, middle-class population. Finally, benevolent citizens regularly encounter professional barriers and bureaucratic ceilings that inhibit their desire to participate. All rhetoric to the contrary notwithstanding, promoting genuine active citizenship is easier said than done. © The Author(s) 2011

Assessing emission reduction targets with dynamic models: deriving target load functions for use in integrated assessment

International audienceInternational agreements to reduce the emission of acidifying sulphur (S) and nitrogen (N) compounds have been negotiated on the basis of an understanding of the link between acidification related changes in soil and surface water chemistry and terrestrial and aquatic biota. The quantification of this link is incorporated within the concept of critical loads. Critical loads are calculated using steady state models and give no indication of the time within which acidified ecosystems might be expected to recover. Dynamic models provide an opportunity to assess the timescale of recovery and can go further to provide outputs which can be used in future emission reduction strategies. In this respect, the Target Load Function (TLF) is proposed as a means of assessing the deposition load necessary to restore a damaged ecosystem to some pre-defined acceptable state by a certain time in the future. A target load represents the deposition of S and N in a defined year (implementation year) for which the critical limit is achieved in a defined time (target year). A TLF is constructed using an appropriate dynamic model to determine the value of a chemical criterion at a given point in time given a temporal pattern of S and N deposition loads. A TLF requires information regarding: (i) the chemical criterion required to protect the chosen biological receptor (i.e. the critical limit); (ii) the year in which the critical limit is required to be achieved; and (iii) time pattern of future emission reductions. In addition, the TLF can be assessed for whole regions to incorporate the effect of these three essentially ecosystem management decisions. Keywords: emission reduction, critical load, target load, dynamic model, recovery tim

Dusty shells surrounding the carbon variables S Scuti and RT Capricorni

For the Mass-loss of Evolved StarS (MESS) programme, the unprecedented spatial resolution of the PACS photometer on board the Herschel space observatory was employed to map the dusty environments of asymptotic giant branch (AGB) and red supergiant (RSG) stars. Among the morphologically heterogeneous sample, a small fraction of targets is enclosed by spherically symmetric detached envelopes. Based on observations in the 70 {\mu}m and 160 {\mu}m wavelength bands, we investigated the surroundings of the two carbon semiregular variables S Sct and RT Cap, which both show evidence for a history of highly variable mass-loss. S Sct exhibits a bright, spherically symmetric detached shell, 138" in diameter and co-spatial with an already known CO structure. Moreover, weak emission is detected at the outskirts, where the morphology seems indicative of a mild shaping by interaction of the wind with the interstellar medium, which is also supported by the stellar space motion. Two shells are found around RT Cap that were not known so far in either dust emission or from molecular line observations. The inner shell with a diameter of 188" shows an almost immaculate spherical symmetry, while the outer ~5' structure is more irregularly shaped. MoD, a modification of the DUSTY radiative transfer code, was used to model the detached shells. Dust temperatures, shell dust masses, and mass-loss rates are derived for both targets

PCA-RECT: An Energy-efficient Object Detection Approach for Event Cameras

We present the first purely event-based, energy-efficient approach for object detection and categorization using an event camera. Compared to traditional frame-based cameras, choosing event cameras results in high temporal resolution (order of microseconds), low power consumption (few hundred mW) and wide dynamic range (120 dB) as attractive properties. However, event-based object recognition systems are far behind their frame-based counterparts in terms of accuracy. To this end, this paper presents an event-based feature extraction method devised by accumulating local activity across the image frame and then applying principal component analysis (PCA) to the normalized neighborhood region. Subsequently, we propose a backtracking-free k-d tree mechanism for efficient feature matching by taking advantage of the low-dimensionality of the feature representation. Additionally, the proposed k-d tree mechanism allows for feature selection to obtain a lower-dimensional dictionary representation when hardware resources are limited to implement dimensionality reduction. Consequently, the proposed system can be realized on a field-programmable gate array (FPGA) device leading to high performance over resource ratio. The proposed system is tested on real-world event-based datasets for object categorization, showing superior classification performance and relevance to state-of-the-art algorithms. Additionally, we verified the object detection method and real-time FPGA performance in lab settings under non-controlled illumination conditions with limited training data and ground truth annotations.Comment: Accepted in ACCV 2018 Workshops, to appea

Soft disks in a narrow channel

The pressure components of "soft" disks in a two dimensional narrow channel are analyzed in the dilute gas regime using the Mayer cluster expansion and molecular dynamics. Channels with either periodic or reflecting boundaries are considered. It is found that when the two-body potential, u(r), is singular at some distance r_0, the dependence of the pressure components on the channel width exhibits a singularity at one or more channel widths which are simply related to r_0. In channels with periodic boundary conditions and for potentials which are discontinuous at r_0, the transverse and longitudinal pressure components exhibit a 1/2 and 3/2 singularity, respectively. Continuous potentials with a power law singularity result in weaker singularities of the pressure components. In channels with reflecting boundary conditions the singularities are found to be weaker than those corresponding to periodic boundaries

Full oral feeding is possible before discharge even in extremely preterm infants

Aim: This study described the steps needed to achieve full oral feeding before discharge in a group of very and extremely preterm (EPT) infants. We analysed the effects of oral feeding skills on discharge timing and on weight gain during their neonatal intensive care unit (NICU) stay. Methods: A prospective cross-sectional observational study of 100 infants who were <32 weeks of gestation (GA) was conducted at the Division of Neonatology, Graz, Austria, from March 2014 to February 2015. Patients were stratified into two groups: those who were <28 weeks at birth and those who were 28 weeks and over. Velocity of oral feeding skills attainment and weight gain were analysed. Results: All infants successfully acquired oral feeding skills during hospitalisation. The median GA at which full oral feeding skills were reached was 37 + 1 weeks in EPT and 34 + 5 weeks in very preterm infants. More immature neonates showed worse feeding performances and lower weight increments during oral feeding steps. Conclusion: Our study confirmed the role of GA in the development of oral feeding skills in the most premature babies. It also raises the question of whether expected daily weight gain should be targeted according to GA