1,308 research outputs found
The East End, the West End, and King's Cross: On Clustering in the Four-Player Hotelling Game
We study experimentally a standard four-player Hotelling game, with a uniform density of consumers and inelastic demand. The pure strategy Nash equilibrium configuration consists of two firms located at one quarter of the ``linear city'', and the other two at three quarters. We do not observe convergence to such an equilibrium. In our experimental data we find three clusters. Besides the direct proximity of the two equilibrium locations this concerns the focal mid-point. Moreover, we observe that whereas this mid-point appears to become more notable over time, other focal points fade away. We explain how these observations are related to best-response dynamics, and to the fact that the players rely on best-responses in particular when they are close to the equilibrium configuration.Location model, Nonconvergence, Focal point, Best-response dynamics
Science and Society in Dialogue About Marker Assisted Selection
Analysis of a European Union funded biotechnology project on plant genomics and marker assisted selection in Solanaceous crops shows that the organization of a dialogue between science and society to accompany technological innovations in plant breeding faces practical challenges. Semi-structured interviews with project participants and a survey among representatives of consumer and other non-governmental organizations show that the professed commitment to dialogue on science and biotechnology is rather shallow and has had limited application for all involved. Ultimately, other priorities tend to prevail because of high workload. The paper recommends including results from previous debates and input from societal groups in the research design phase (prior to communication), to use appropriate media to disseminate information and to make explicit how societal feedback is used in research, in order to facilitate true dialogue between science and society on biotechnology
MRS: a fast and compact retrieval system for biological data
The biological data explosion of the ‘omics’ era requires fast access to many data types in rapidly growing data banks. The MRS server allows for very rapid queries in a large number of flat-file data banks, such as EMBL, UniProt, OMIM, dbEST, PDB, KEGG, etc. This server combines a fast and reliable backend with a very user-friendly implementation of all the commonly used information retrieval facilities. The MRS server is freely accessible at . Moreover, the MRS software is freely available at for those interested in making their own data banks available via a web-based server
Size segregation in a granular bore
We investigate the effect of particle-size segregation in an upslope propagating granular bore. A bidisperse mixture of particles, initially normally graded, flows down an inclined chute and impacts with a closed end. This impact causes the formation of a shock in flow thickness, known as a granular bore, to travel upslope, leaving behind a thick deposit. This deposit imprints the local segregated state featuring both pure and mixed regions of particles as a function of downstream position. The particle-size distribution through the depth is characterized by a thin purely small-particle layer at the base, a significant linear transition region, and a thick constant mixed-particle layer below the surface, in contrast to previously observed S-shaped steady-state concentration profiles. The experimental observations agree with recent progress that upward and downward segregation of large and small particles respectively is asymmetric. We incorporate the three-layer, experimentally observed, size-distribution profile into a depth-averaged segregation model to modify it accordingly. Numerical solutions of this model are able to match our experimental results and therefore motivate the use of a more general particle-size distribution profile
Conformational Transitions Accompanying Oligomerization of Yeast Alcohol Oxidase, a Peroxisomal Flavoenzyme
Alcohol oxidase (AO) is a homo-octameric flavoenzyme which catalyzes methanol oxidation in methylotrophic yeasts. AO protein is synthesized in the cytosol and subsequently sorted to peroxisomes where the active enzyme is formed. To gain further insight in the molecular mechanisms involved in AO activation, we studied spectroscopically native AO from Hansenula polymorpha and Pichia pastoris and three putative assembly intermediates. Fluorescence studies revealed that both Trp and FAD are suitable intramolecular markers of the conformation and oligomeric state of AO. A direct relationship between dissociation of AO octamers and increase in Trp fluorescence quantum yield and average fluorescence lifetime was found. The time-resolved fluorescence of the FAD cofactor showed a rapid decay component which reflects dynamic quenching due to the presence of aromatic amino acids in the FAD-binding pocket. The analysis of FAD fluorescence lifetime profiles showed a remarkable resemblance of pattern for purified AO and AO present in intact yeast cells. Native AO contains a high content of ordered secondary structure which was reduced upon FAD-removal. Dissociation of octamers into monomers resulted in a conversion of β-sheets into α-helices. Our results are explained in relation to a 3D model of AO, which was built based on the crystallographic data of the homologous enzyme glucose oxidase from Aspergillus niger. The implications of our results for the current model of the in vivo AO assembly pathway are discussed.
Reply to comment by B. Andreotti et al. on "Solving the mystery of booming sand dunes"
This reply addresses three main issues raised in the
comment of Andreotti et al. [2008]. First, the turning of
ray paths in a granular material does not preclude the
propagation of body waves and the resonance condition
described by Vriend et al. [2007]. The waveguide model
still holds in the dune for the observed velocities, even
with a velocity increase with depth as implied by Andreotti
et al. [2008]. Secondly, the method of initiation of
spontaneous avalanching does not influence the booming
frequency. The frequency is independent of the source
once sustained booming starts; it depends on the subsurface
structure of the dune. Thirdly, if all data points from Vriend
et al. [2007] are included in the analysis (and not an
average or selection), no correlation is observed between
the sustained booming frequency and average particle
diameter
Solving the mystery of booming sand dunes
Desert booming can be heard after a natural slumping
event or during a sand avalanche generated by humans
sliding down the slip face of a large dune. The sound is
remarkable because it is composed of one dominant audible
frequency (70 to 105 Hz) plus several higher harmonics.
This study challenges earlier reports that the dunes’
frequency is a function of average grain size by
demonstrating through extensive field measurements that
the booming frequency results from a natural waveguide
associated with the dune. The booming frequency is fixed
by the depth of the surficial layer of dry loose sand that is
sandwiched between two regions of higher compressional
body wave velocity. This letter presents measurements of
the booming frequencies, compressional wave velocities,
depth of surficial layer, along with an analytical prediction
of the frequency based on constructive interference of
propagating waves generated by avalanching along the dune
surface
The probabilistic nature of dune collisions in 2D
Dunes are bedforms of different size and shape, appearing throughout aeolian, subaqueous and extraterrestrial environments. Collisions between dunes drive dune field evolution, and are a direct result of interacting dunes of different heights, travelling at different speeds. We perform 2D cellular automaton simulations of collisions between dune pairs migrating in a steady flow. Modelled collisions can result in either ejection, where dunes exchange mass before separating, or downstream- or upstream-dominant coalescence (merging of dunes). For each of these three elementary types of interaction, we identify the mass exchange mechanism and the distinctive intermediate morphologies. Surprisingly, we show that the collision outcome depends probabilistically on the initial dune area ratio r and can be described by a narrow sigmoidal function centred on r=1/2. Finally, we compare our simulations with laboratory experiments of dune collisions, finding good agreement concerning the intermediate morphology and the collision outcome. Our results can motivate further observational or experimental studies that validate our probabilistic collision predictions and fully determine the controls on the coalescence–ejection transition.</p
- …