Nanomechanical effects in an Andreev quantum dot

We consider a quantum dot with mechanical degrees of freedom which is coupled to superconducting electrodes. A Josephson current is generated by applying a phase difference. In the absence of coupling to vibrations, this setup was previously proposed as a detector of magnetic flux and we wish here to address the effect of the phonon coupling to this detection scheme. We compute the charge on the quantum dot and determine its dependence on the phase difference in the presence of phonon coupling and Coulomb interaction. This allows to identify regions in parameter space with the highest charge to phase sensitivity, which are relevant for flux detection. Further insight about the interplay of such couplings and subsequent entanglement properties between electron and phonon degrees of freedom are gained by computing the von Neuman entropy.Comment: 9 pages, 7 figures; minor corretion

Supervised Classification Using Sparse Fisher's LDA

It is well known that in a supervised classification setting when the number of features is smaller than the number of observations, Fisher's linear discriminant rule is asymptotically Bayes. However, there are numerous modern applications where classification is needed in the high-dimensional setting. Naive implementation of Fisher's rule in this case fails to provide good results because the sample covariance matrix is singular. Moreover, by constructing a classifier that relies on all features the interpretation of the results is challenging. Our goal is to provide robust classification that relies only on a small subset of important features and accounts for the underlying correlation structure. We apply a lasso-type penalty to the discriminant vector to ensure sparsity of the solution and use a shrinkage type estimator for the covariance matrix. The resulting optimization problem is solved using an iterative coordinate ascent algorithm. Furthermore, we analyze the effect of nonconvexity on the sparsity level of the solution and highlight the difference between the penalized and the constrained versions of the problem. The simulation results show that the proposed method performs favorably in comparison to alternatives. The method is used to classify leukemia patients based on DNA methylation features

An Experimental Test of Precautionary Bidding

Auctions often involve goods exhibiting a common knowledge ex-post risk that is independent of buyers’ private values or their signals regarding common value components. Esö and White (2004) showed theoretically that ex-post risk leads to precautionary bidding for DARA bidders: Agents reduce their bids by more than their appropriate risk premium. Testing precautionary bidding with data from the field seems almost impossible. We conduct experimental first-price auctions that allow us to directly identify the precautionary premium and find clear evidence for precautionary bidding. Bidders are significantly better off when a risky object rather than an equally valued sure object is auctioned. Our results are robust if we control for potentially confounding decision biases

On the Disalignment of Interstellar Grains

Several mechanisms have been proposed to explain the alignment of grains with the interstellar magnetic field, including paramagnetic dissipation, radiative torques, and supersonic gas-grain streaming. These must compete with disaligning processes, including randomly directed torques arising from collisions with gas atoms. I describe a novel disalignment mechanism for grains that have a time-varying electric dipole moment and that drift across the magnetic field. Depending on the drift speed, this mechanism may yield a much shorter disalignment timescale than that associated with random gas atom impacts. For suprathermally rotating grains, the new disaligning process may be more potent for carbonaceous dust than for silicate dust. This could result in efficient alignment for silicate grains but poor alignment for carbonaceous grains.Comment: 19 pages, 3 figures, submitted to Ap

Tempus Fugit: Time Pressure in Risky Decisions

We study the effects of time pressure on risky decisions for pure gain prospects, pure loss prospects, and mixed prospects involving both gains and losses. In an experiment we find that risk aversion for gains is robust under time pressure whereas risk seeking for losses turns into risk aversion under time pressure. For mixed prospects, subjects become more loss averse and more gain seeking under time pressure, depending on the framing of the prospects. The results suggest the importance of aspiration levels under time pressure. We discuss the implications of our findings for decision making situations that involve time pressure

Cryogenic seal remains leaktight during thermal displacement

Cryogenic seals protect the surfaces of a plastic member in a low-pressure system subjected to extreme temperature changes. The outer seal is an aluminum expansion ring bonded to the lens outer surface and the inner seal consists of a resin-filled aluminum U-ring bonded to the inner surface