The tangential velocity of M31: CLUES from constrained simulations

Determining the precise value of the tangential component of the velocity of M31 is a non trivial astrophysical issue, that relies on complicated modeling. This has recently lead to con- flicting estimates, obtained by several groups that used different methodologies and assump- tions. This letter addresses the issue by computing a Bayesian posterior distribution function of this quantity, in order to measure the compatibility of those estimates with LambdaCDM. This is achieved using an ensemble of local group (LG) look-alikes collected from a set of Con- strained Simulations (CSs) of the local Universe, and a standard unconstrained LambdaCDM. The latter allows us to build a control sample of LG-like pairs and to single out the influence of the environment in our results. We find that neither estimate is at odds with LambdaCDM; how- ever, whereas CSs favour higher values of vtan , the reverse is true for estimates based on LG samples gathered from unconstrained simulations, overlooking the environmental elementComment: 5 pages, 2 figures, accepted for publications in MNRAS Letter

Fluctuating Currents in Stochastic Thermodynamics II. Energy Conversion and Nonequilibrium Response in Kinesin Models

Unlike macroscopic engines, the molecular machinery of living cells is strongly affected by fluctuations. Stochastic Thermodynamics uses Markovian jump processes to model the random transitions between the chemical and configurational states of these biological macromolecules. A recently developed theoretical framework [Wachtel, Vollmer, Altaner: "Fluctuating Currents in Stochastic Thermodynamics I. Gauge Invariance of Asymptotic Statistics"] provides a simple algorithm for the determination of macroscopic currents and correlation integrals of arbitrary fluctuating currents. Here, we use it to discuss energy conversion and nonequilibrium response in different models for the molecular motor kinesin. Methodologically, our results demonstrate the effectiveness of the algorithm in dealing with parameter-dependent stochastic models. For the concrete biophysical problem our results reveal two interesting features in experimentally accessible parameter regions: The validity of a non-equilibrium Green--Kubo relation at mechanical stalling as well as negative differential mobility for superstalling forces.Comment: PACS numbers: 05.70.Ln, 05.40.-a, 87.10.Mn, 87.16.Nn. An accompanying publication "Fluctuating Currents in Stochastic Thermodynamics I. Gauge Invariance of Asymptotic Statistics" is available at http://arxiv.org/abs/1407.206

Constraints on the origin of the first light from SN2014J

We study the very early lightcurve of supernova 2014J (SN 2014J) using the high-cadence broad-band imaging data obtained by the Kilodegree Extremely Little Telescope (KELT), which fortuitously observed M 82 around the time of the explosion, starting more than two months prior to detection, with up to 20 observations per night. These observations are complemented by observations in two narrow-band filters used in an H$\alpha$ survey of nearby galaxies by the intermediate Palomar Transient Factory (iPTF) that also captured the first days of the brightening of the \sn. The evolution of the lightcurves is consistent with the expected signal from the cooling of shock heated material of large scale dimensions, \gsim 1 R_{\odot}. This could be due to heated material of the progenitor, a companion star or pre-existing circumstellar environment, e.g., in the form of an accretion disk. Structure seen in the lightcurves during the first days after explosion could also originate from radioactive material in the outer parts of an exploding white dwarf, as suggested from the early detection of gamma-rays. The model degeneracy translates into a systematic uncertainty of $\pm 0.3$ days on the estimate of the first light from SN 2014J.Comment: Accepted by ApJ. Companion paper by Siverd et al, arXiv:1411.415

Climate based facade design for business buildings with examples from central London

There is a disconnection between commercial architecture and environmental thinking, where green features can be included as part of a strategy for gaining approvals and marketing projects, but those features are not reviewed after completion and occupation of the building and knowledge is not shared. High levels of air conditioning are still considered unavoidable. Elaborate double skin façades and complex motorized shading systems are adopted; often masking an underlying lack of basic environmental thinking. This article returns (in principle) to the physics of comfort in buildings and the passive strategies which can help achieve this with a low energy and carbon footprint. Passive and active façade design strategies are outlined as the basis of a critical tool and a design methodology for new projects. A new architectural sensibility can arise based on modeling the inputs of sunlight, daylight and air temperature in time and space at the early stages of design. Early but sound strategies can be tested and refined using advanced environmental modeling techniques. Architecture and environmental thinking can proceed hand in hand through the design process

Agent Based Models and Opinion Dynamics as Markov Chains

This paper introduces a Markov chain approach that allows a rigorous analysis of agent based opinion dynamics as well as other related agent based models (ABM). By viewing the ABM dynamics as a micro description of the process, we show how the corresponding macro description is obtained by a projection construction. Then, well known conditions for lumpability make it possible to establish the cases where the macro model is still Markov. In this case we obtain a complete picture of the dynamics including the transient stage, the most interesting phase in applications. For such a purpose a crucial role is played by the type of probability distribution used to implement the stochastic part of the model which defines the updating rule and governs the dynamics. In addition, we show how restrictions in communication leading to the co-existence of different opinions follow from the emergence of new absorbing states. We describe our analysis in detail with some specific models of opinion dynamics. Generalizations concerning different opinion representations as well as opinion models with other interaction mechanisms are also discussed. We find that our method may be an attractive alternative to mean-field approaches and that this approach provides new perspectives on the modeling of opinion exchange dynamics, and more generally of other ABM.Comment: 26 pages, 12 figure