Properties of selected mutations and genotypic landscapes under Fisher's Geometric Model

The fitness landscape - the mapping between genotypes and fitness - determines properties of the process of adaptation. Several small genetic fitness landscapes have recently been built by selecting a handful of beneficial mutations and measuring fitness of all combinations of these mutations. Here we generate several testable predictions for the properties of these landscapes under Fisher's geometric model of adaptation (FGMA). When far from the fitness optimum, we analytically compute the fitness effect of beneficial mutations and their epistatic interactions. We show that epistasis may be negative or positive on average depending on the distance of the ancestral genotype to the optimum and whether mutations were independently selected or co-selected in an adaptive walk. Using simulations, we show that genetic landscapes built from FGMA are very close to an additive landscape when the ancestral strain is far from the optimum. However, when close to the optimum, a large diversity of landscape with substantial ruggedness and sign epistasis emerged. Strikingly, landscapes built from different realizations of stochastic adaptive walks in the same exact conditions were highly variable, suggesting that several realizations of small genetic landscapes are needed to gain information about the underlying architecture of the global adaptive landscape.Comment: 51 pages, 8 figure

Front-end electronics for ATLAS pixel detector

Large advances have been made over the last years in the development of rad-soft readout chip prototypes, closing the first phase of the ATLAS pixel [2] demonstrator programme. The next step of this programme is aimed at realizing a full scale pixel front-end chip using two rad-hard technologies. The DMILL chip has been received in Oct. 99 and the deep submicron design is currently under development. Measurements on the DMILL ATLAS pixel Front-end chip are presented

On filtering in the viscous-convective subrange for turbulent mixing of high Schmidt number passive scalars

In the present work, we investigate the possibility of performing velocity-resolved, scalar-filtered (VR-SF) numerical simulations of turbulent mixing of high Schmidt number scalars, by using a Large Eddy Simulation (LES)-type filter in the viscous-convective subrange. The only requirement for this technique is the large scale separation between the Kolmogorov and Batchelor length scales, which is a direct outcome of the high Schmidt number of the scalar. The present a priori analysis using high fidelity direct numerical simulation data leads to two main observations. First, the missing triadic interactions between (resolved) velocity and (filtered-out) scalar modes in the viscous-convective subrange do not affect directly the large scales. Second, the magnitude of the subgrid term is shown to be extremely small, which makes it particularly susceptible to numerical errors associated with the scalar transport scheme. A posteriori tests indicate that upwinded schemes, generally used for LES in complicated geometries, are sufficiently dissipative to overwhelm any contribution from the subgrid term. This renders the subgrid term superfluous, and as a result, VR-SF simulations run without subgrid scalar flux models are able to preserve large scale transport characteristics with remarkable accuracy

Subfilter scalar-flux vector orientation in homogeneous isotropic turbulence

The geometric orientation of the subfilter-scale scalar-flux vector is examined in homogeneous isotropic turbulence. Vector orientation is determined using the eigenframe of the resolved strain-rate tensor. The Schmidt number is kept sufficiently large so as to leave the velocity field, and hence the strain-rate tensor, unaltered by filtering in the viscous-convective subrange. Strong preferential alignment is observed for the case of Gaussian and box filters, whereas the sharp-spectral filter leads to close to a random orientation. The orientation angle obtained with the Gaussian and box filters is largely independent of the filter width and the Schmidt number. It is shown that the alignment direction observed numerically using these two filters is predicted very well by the tensor-diffusivity model. Moreover, preferred alignment of the scalar gradient vector in the eigenframe is shown to mitigate any probable issues of negative diffusivity in the tensor-diffusivity model. Consequentially, the model might not suffer from solution instability when used for large eddy simulations of scalar transport in homogeneous isotropic turbulence. Further a priori tests indicate poor alignment of the Smagorinsky and stretched vortex model predictions with the exact subfilter flux. Finally, strong filter dependence of subfilter scalar-flux orientation suggests that explicit filtering may be preferable to implicit filtering in large eddy simulations

Twitter influence and cumulative perceptions of extremist support: A case study of Geert Wilders

The advent of Social media has changed the manner in which perceptions about power and information can be influenced. Twitter is used as a fast‐paced vehicle to deliver short, succinct pieces of information, creating the perception of acceptance, popularity and authority. In the case of extremist groups, Twitter is one of several avenues to create the perception of endorsement of values that would otherwise gain less prominence through mainstream media. This study examines the use of Twitter in augmenting the status and reputation of anti‐Islam and anti‐immigration policy through the controlled release of social media information bursts. The paper demonstrates the use of new media by extremist groups using open source case study data from the associated Twitter traffic of Geert Wilders. The results indicate the pursuit of increased traction for controversial ideals that provoke and incite others towards extremism, violence, racism and Islamaphobia

Development of a radiation hard version of the Analog Pipeline Chip APC128

The Analog Pipeline Chip (APC) is a low noise, low power readout chip for silicon micro strip detectors with 128 channels containing an analog pipeline of 32 buffers depth. The chip has been designed for operation at HERA with a power dissipation of 300-400 muW per channel and has been used also in several other particle physics experiments. In this paper we describe the development of a radiation hard version of this chip that will be used in the H1 vertex detector for operation at the luminosity upgraded HERA machine. A 128 channel prototyping chip with several amplifier variations has been designed in the radiation hard DMILL technology and measured. The results of various parameter variations are presented in this paper. Based on this, the design choice for the final production version of the APC128-DMILL has been made.Comment: 10 pages, 10 figure

Predicting aromatic exciplex fluorescence emission energies

PAH dimerization has been widely posited to play an important, even rate-determining role in soot nucleation, despite scanty experimental evidence of the existence of PAH dimers in flames. Laser-induced fluorescence (LIF) offers a promising in situ method of identifying PAH dimers, if dimer fluorescence can be distinguished from the fluorescence of the constituent monomers and other species present. Predicting transition energies for excited dimers (excimers) and excited complexes (exciplexes) represents a significant challenge for theory. Nonempirically tuned LC-BLYP functionals have been used to compute excited-state geometries and emission energies for a database of 81 inter- and intramolecular PAH excimers and exciplexes. Exciplex emission energies depend sensitively on the topology of the PAHs involved, but a linear relationship between the mean monomer bandgap and the computed exciplex emission means that dimer electronic properties can be predicted based on the properties of the constituent monomers. The range of fluorescence energies calculated for structures containing small to moderately-sized PAHs indicates that either noncovalent or aliphatically-linked complexes could generate the visible-range fluorescence energies observed in LIF experiments

Grande vitesse ferroviaire et développement économique local : une revue de la littérature

Des projets de lignes à grande vitesse existent dans de nombreux pays. Les acteurs économiques des territoires desservis ou qui le seront, ont eu ou ont de multiples attentes concernant cette desserte qui modifie l'accessibilité de leurs territoires : dynamisme économique, arrivée de nouvelles entreprises et populations, développement du tourisme, ou de projets immobiliers résidentiels et de bureaux autour des gares, etc. La permanence de ces attentes, alors que le mythe des effets structurants des infrastructures de transport a depuis longtemps été remis en question dans la littérature académique, est à l'origine de notre questionnement. L'objectif de cette communication est de présenter une revue de la littérature académique mais également non académique relative aux effets de la grande vitesse ferroviaire sur le développement local afin d'identifier les raisons de cette déconnexion entre les travaux académiques et les discours politiques.GRANDE VITESSE ; ECONOMIE ; DEVELOPPEMENT ; INFRASTRUCTURE de TRANSPORT

Pratiques collaboratives et démarche environnementale dans la supply chain : mythe ou réalité ?

L'objectif de cette recherche est d'éclairer la diversité des pratiques collaboratives et leur possible déclinaison dans une démarche environnementale commune aux acteurs de la collaboration. Plus particulièrement, il s'agit d'illustrer des pratiques collaboratives différentes et de décrire la manière dont est prise en compte la contrainte environnementale dans chacune d'entre elles. Nous nous appuyons sur sept monographies de collaboration appartenant à divers secteurs d'activité et étapes de la supply chain. Cette démarche exploratoire nous permet de poser l'hypothèse que les formes de proximité entre les acteurs déterminent des modes de collaboration spécifiques et des logiques de mise au vert de la chaîne particulières.Pratiques collaborative ; supply chain verte ; études de cas ; typologie

Effect of a splitter plate on the dynamics of a vortex pair

An experimental and numerical study was performed to investigate and compare the behavior of a counter-rotating vortex pair and a single vortex in the vicinity of a wall. This analysis is motivated by the theoretical equivalence, in the inviscid limit, between these two configurations. A wind tunnel with two NACA0012 profiles mounted vertically with an optional splitter plate in the center and a stereoscopic particle image velocimetry system was used to experimentally study these interactions. Many significant differences were found between the two configurations, including the growth of the Crow instability in the two vortex configuration, but not in the one vortex/wall configuration. The numerical results re-enforced the experimental results, and emphasized the fundamental physical differences between the two configurations. While modeling a vortex wall system with an image vortex may give correct integral results for loads experienced by blades, this model does not accurately describe the downstream dynamics of the vortex system