Search by Committee

We consider the problem of sequential search when the decision to stop searching is made by a committee. We show that a symmetric stationary equilibrium exists and is unique given that the distribution of rewards is log concave. Committee members set a lower acceptance threshold than do single-agent searchers. In addition, mean preserving spreads in the distribution of rewards may lower each member's continuation value | an impossibility in the single-agent setting. If committee members are very patient or very impatient, expected search duration is lower than it would be for a single agent, but, for intermediate levels of patience, this comparison may be reversed. Holding the fraction of votes required to stop fixed, expected search duration rises with committee size on patient committees but falls with committee size on impatient committees. Finally, we consider the effect of varying the number of votes required to stop, holding committee size constant. We show that the welfare-maximizing vote threshold increases in the rate of patience and that there is a finite bound on patience such that unanimity is welfare maximizing.sequential search, voting, committees

A Matching Model of the Housing Market: Searching for a Motivated Partner

We construct a bilateral search model of the housing market in which agents differ in their flow rewards while searching. Buyers and sellers enter the market with high flow rewards, but move at a Poisson rate to a state with low flow rewards if they do not transact in the meantime. We characterize the equilibrium steady state matching pattern and compare this to the constrained efficient matching pattern. In particular we show that equilibrium is characterized by too little /Opportunistic Matching/, in which agents with high flow values will match only with agents with low flow values. We also characterize the joint distribution of price and time to sale (for sellers). The expected price conditional on time to sale falls with time spent on the market, while the conditional variance of price first rises and then falls with time on the market.

Search by committee

We consider the problem of sequential search when the decision to stop searching is made by a committee. We show that a symmetric stationary equilibrium exists and is unique given that the distribution of rewards is log concave. Committee members set a lower acceptance threshold than do single-agent searchers. In addition, mean preserving spreads in the distribution of rewards may lower each member's continuation value - an impossibility in the single-agent setting. If committee members are very patient or very impatient, expected search duration is lower than it would be for a single agent, but, for intermediate levels of patience, this comparison may be reversed. Holding the fraction of votes required to stop fixed, expected search duration rises with committee size on patient committees but falls with committee size on impatient committees. Finally, we consider the effect of varying the number of votes required to stop, holding committee size constant. We show that the welfare-maximizing vote threshold increases in the rate of patience and that there is a finite bound on patience such that unanimity is welfare maximizing

Integrative analysis of the heat shock response in Aspergillus fumigatus

<p>Abstract</p> <p>Background</p> <p><it>Aspergillus fumigatus </it>is a thermotolerant human-pathogenic mold and the most common cause of invasive aspergillosis (IA) in immunocompromised patients. Its predominance is based on several factors most of which are still unknown. The thermotolerance of <it>A. fumigatus </it>is one of the traits which have been assigned to pathogenicity. It allows the fungus to grow at temperatures up to and above that of a fevered human host. To elucidate the mechanisms of heat resistance, we analyzed the change of the <it>A. fumigatus </it>proteome during a temperature shift from 30°C to 48°C by 2D-fluorescence difference gel electrophoresis (DIGE). To improve 2D gel image analysis results, protein spot quantitation was optimized by missing value imputation and normalization. Differentially regulated proteins were compared to previously published transcriptome data of <it>A. fumigatus</it>. The study was augmented by bioinformatical analysis of transcription factor binding sites (TFBSs) in the promoter region of genes whose corresponding proteins were differentially regulated upon heat shock.</p> <p>Results</p> <p>91 differentially regulated protein spots, representing 64 different proteins, were identified by mass spectrometry (MS). They showed a continuous up-, down- or an oscillating regulation. Many of the identified proteins were involved in protein folding (chaperones), oxidative stress response, signal transduction, transcription, translation, carbohydrate and nitrogen metabolism. A correlation between alteration of transcript levels and corresponding proteins was detected for half of the differentially regulated proteins. Interestingly, some previously undescribed putative targets for the heat shock regulator Hsf1 were identified. This provides evidence for Hsf1-dependent regulation of mannitol biosynthesis, translation, cytoskeletal dynamics and cell division in <it>A. fumigatus</it>. Furthermore, computational analysis of promoters revealed putative binding sites for an AP-2alpha-like transcription factor upstream of some heat shock induced genes. Until now, this factor has only been found in vertebrates.</p> <p>Conclusions</p> <p>Our newly established DIGE data analysis workflow yields improved data quality and is widely applicable for other DIGE datasets. Our findings suggest that the heat shock response in <it>A. fumigatus </it>differs from already well-studied yeasts and other filamentous fungi.</p

Evidence for a Ru4+^{4+} Kondo Lattice in LaCu3_3Ru4_4O12_{12}

Rare $d$-electron derived heavy-fermion properties of the solid-solution series LaCu$_3$Ru$_x$Ti$_{4-x}$O$_{12}$ were studied for $1 \leq x \leq 4$ by resistivity, susceptibility, specific-heat measurements, and magnetic-resonance techniques. The pure ruthenate ($x = 4$) is a heavy-fermion metal characterized by a resistivity proportional to $T^2$ at low temperatures $T$. The coherent Kondo lattice formed by the localized Ru 4$d$ electrons is screened by the conduction electrons leading to strongly enhanced effective electron masses. By increasing titanium substitution the Kondo lattice becomes diluted resulting in single-ion Kondo properties like in the paradigm $4f$-based heavy-fermion compound Ce$_x$La$_{1-x}$Cu$_{2.05}$Si$_2$ [M. Ocko {\em et al.}, Phys. Rev. B \textbf{64}, 195106 (2001)]. In LaCu$_3$Ru$_x$Ti$_{4-x}$O$_{12}$ the heavy-fermion behavior finally breaks down on crossing the metal-to-insulator transition close to $x = 2$.Comment: 9 pages, 8 figure

Numerical modeling of shallow landslide impacts on flexible protection systems and its validation with full scale testing

Innovative flexible protection barriers against shallow landslides, made from high tensile steel meshes, demanded the development of numerical models for the different mesh types accompanied with 1:1 scale prototype field testing. To generate the barrier model, a special Discrete Element had to be developed that represents the chain link type of steel mesh. It was crucial that it includes the complex out-of-plane height of the mesh that accomodates the local high deformations of the net. The filling process of the barrier is simulated using OpenFOAM, taking the fluid-structure interaction with high deformations into account. In addition to the shear thinning behaviour of the mud, the turbulence in form of a large eddy simulation can be introduced, having regard to the interaction with the complex geometry and free surface by a Dynamic Mixed Model approach for the subgrid scales. The model is validated with 1:1 scale tests where shots of 50 m3 of mud travel down a 40 m long slope and hit the barrier

The Charcot-Marie tooth disease mutation R94Q in MFN2 decreases ATP production but increases mitochondrial respiration under conditions of mild oxidative stress

Charcot–Marie tooth disease is a hereditary polyneuropathy caused by mutations in Mitofusin-2 (MFN2), a GTPase in the outer mitochondrial membrane involved in the regulation of mitochondrial fusion and bioenergetics. Autosomal-dominant inheritance of a R94Q mutation in MFN2 causes the axonal subtype 2A2A which is characterized by early onset and progressive atrophy of distal muscles caused by motoneuronal degeneration. Here, we studied mitochondrial shape, respiration, cytosolic, and mitochondrial ATP content as well as mitochondrial quality control in MFN2-deficient fibroblasts stably expressing wildtype or R94Q MFN2. Under normal culture conditions, R94Q cells had slightly more fragmented mitochondria but a similar mitochondrial oxygen consumption, membrane potential, and ATP production as wildtype cells. However, when inducing mild oxidative stress 24 h before analysis using 100 µM hydrogen peroxide, R94Q cells exhibited significantly increased respiration but decreased mitochondrial ATP production. This was accompanied by increased glucose uptake and an up-regulation of hexokinase 1 and pyruvate kinase M2, suggesting increased pyruvate shuttling into mitochondria. Interestingly, these changes coincided with decreased levels of PINK1/Parkin-mediated mitophagy in R94Q cells. We conclude that mitochondria harboring the disease-causing R94Q mutation in MFN2 are more susceptible to oxidative stress, which causes uncoupling of respiration and ATP production possibly by a less efficient mitochondrial quality control