Optimal Tradeoff Between Exposed and Hidden Nodes in Large Wireless Networks

Wireless networks equipped with the CSMA protocol are subject to collisions due to interference. For a given interference range we investigate the tradeoff between collisions (hidden nodes) and unused capacity (exposed nodes). We show that the sensing range that maximizes throughput critically depends on the activation rate of nodes. For infinite line networks, we prove the existence of a threshold: When the activation rate is below this threshold the optimal sensing range is small (to maximize spatial reuse). When the activation rate is above the threshold the optimal sensing range is just large enough to preclude all collisions. Simulations suggest that this threshold policy extends to more complex linear and non-linear topologies

The Dirichlet Obstruction in AdS/CFT

The obstruction for a perturbative reconstruction of the five-dimensional bulk metric starting from the four-dimensional metric at the boundary,that is, the Dirichlet problem, is computed in dimensions $6\leq d\leq 10$ and some comments are made on its general structure and, in particular, on its relationship with the conformal anomaly, which we compute in dimension $d=8$.Comment: 13 pages, references added (this paper supersedes hep-th/0206140, "A Note on the Bach Tensor in AdS/CFT", which has been withdrawn

Are tearful individuals perceived as less competent? Probably not

What are the social signals of emotional tears? This question has fascinated scholars ever since Darwin. Studies have suggested several interpersonal effects of emotional tears. A recent study by Van de Ven, Meijs, and Vingerhoets (2017) presented evidence in three studies that tearful individuals are perceived as warmer, but also less competent than their non-tearful counterparts. However, the competence effect was relatively small, and a recent replication failed to find such an effect in two different populations while the warmth effect was replicated (Zickfeld & Schubert, 2018). This questions the generalizability of the effect of tears on perceived competence. To test whether individuals expressing emotional tears are really perceived as less competent and what boundary conditions such an effect might have, we specified a decision tree of three different studies in which we test differences between the original reference study and the replication. We replicated previous findings of the perceived (in)competence in Study 1 (n = 531) but observed a considerably smaller non-significant effect when proceeding to Study 2 (n = 471), which increased the number of stimuli. The earlier and now repeated replication failure can therefore likely be attributed to an increased variation in stimulus material. We conclude that there is not enough evidence to argue that one social outcome of tears signals a relative lack of competence as the effect seems to depend on the specific stimuli used.info:eu-repo/semantics/acceptedVersio

Slipping friction of an optically and magnetically manipulated microsphere rolling at a glass-water interface

The motion of submerged magnetic microspheres rolling at a glass-water interface has been studied using magnetic rotation and optical tweezers combined with bright-field microscopy particle tracking techniques. Individual microspheres of varying surface roughness were magnetically rotated both in and out of an optical trap to induce rolling, along either plain glass cover slides or glass cover slides functionalized with polyethylene glycol. It has been observed that the manipulated microspheres exhibited nonlinear dynamic rolling-while-slipping motion characterized by two motional regimes: At low rotational frequencies, the speed of microspheres free-rolling along the surface increased proportionately with magnetic rotation rate; however, a further increase in the rotation frequency beyond a certain threshold revealed a sharp transition to a motion in which the microspheres slipped with respect to the external magnetic field resulting in decreased rolling speeds. The effects of surface-microsphere interactions on the position of this threshold frequency are posed and investigated. Similar experiments with microspheres rolling while slipping in an optical trap showed congruent results.Comment: submitted to Journal of Applied Physics, 11 figure

A study of rotating globular clusters - the case of the old, metal-poor globular cluster NGC 4372

Aims: We present the first in-depth study of the kinematic properties and derive the structural parameters of NGC 4372 based on the fit of a Plummer profile and a rotating, physical model. We explore the link between internal rotation to different cluster properties and together with similar studies of more GCs, we put these in the context of globular cluster formation and evolution. Methods: We present radial velocities for 131 cluster member stars measured from high-resolution FLAMES/GIRAFFE observations. Their membership to the GC is additionally confirmed from precise metallicity estimates. Using this kinematic data set we build a velocity dispersion profile and a systemic rotation curve. Additionally, we obtain an elliptical number density profile of NGC 4372 based on optical images using a MCMC fitting algorithm. From this we derive the cluster's half-light radius and ellipticity as r_h=3.4'+/-0.04' and e=0.08+/-0.01. Finally, we give a physical interpretation of the observed morphological and kinematic properties of this GC by fitting an axisymmetric, differentially rotating, dynamical model. Results: Our results show that NGC 4372 has an unusually high ratio of rotation amplitude to velocity dispersion (1.2 vs. 4.5 km/s) for its metallicity. This, however, puts it in line with two other exceptional, very metal-poor GCs - M 15 and NGC 4590. We also find a mild flattening of NGC 4372 in the direction of its rotation. Given its old age, this suggests that the flattening is indeed caused by the systemic rotation rather than tidal interactions with the Galaxy. Additionally, we estimate the dynamical mass of the GC M_dyn=2.0+/-0.5 x 10^5 M_Sun based on the dynamical model, which constrains the mass-to-light ratio of NGC 4372 between 1.4 and 2.3 M_Sun/L_Sun, representative of an old, purely stellar population.Comment: Accepted for publication in A&A, 12 pages, 14 figures, 2 table

Discovery of a Quadruple Lens in CANDELS with a Record Lens Redshift z=1.53

Using spectroscopy from the Large Binocular Telescope and imaging from the Hubble Space Telescope we discovered the first strong galaxy lens at z(lens)>1. The lens has a secure photometric redshift of z=1.53+/-0.09 and the source is spectroscopically confirmed at z=3.417. The Einstein radius (0.35"; 3.0 kpc) encloses 7.6 x 10^10 Msol, with an upper limit on the dark matter fraction of 60%. The highly magnified (40x) source galaxy has a very small stellar mass (~10^8 Msol) and shows an extremely strong [OIII]_5007A emission line (EW_0 ~ 1000A) bolstering the evidence that intense starbursts among very low-mass galaxies are common at high redshift.Comment: accepted for publication in ApJ Letter

Evaluating integrated impacts of low-emission transitions in the livestock sector

This paper provides the results of a combined qualitative and quantitative assessment of key impacts for two low-emission transition pathways for the Dutch livestock sector. These impacts or side-effects can be positive or negative. Both pathways were designed to meet a sector specific methane emission reduction target of 33 % in 2030 (relative to 2005). The qualitative assessment with stakeholders resulted in developing off-model quantifications to better reflect expected changes in system dynamics and development of more realistic transition pathways used for macro-econometric (E3ME) and atmospheric (TM5-FASST) modelling. We found that each low-emission transition pathway has a unique footprint of positive and negative impacts. This footprint is largely shaped by the combination of existing and new technologies, infrastructure used, and practices deployed. We consider the analysis and results relevant for climate policy and governance processes where there is a need to develop transition pathways that are optimised to meet different sustainable development goals. © 2019 The Author(s

Effect of a Fast-Skin 'Body' Suit on drag during front crawl swimming

The effect on drag of a Speedo Fast‐skin suit compared to a conventional suit was studied in 13 subjects (6 males, 7 females) swimming at different velocities between 1.0 and 2.0 m•