Ramp wave loading experiments driven by heavy ion beams: a feasibility study

A new design for heavy-ion beam driven ramp wave loading experiments is suggested and analyzed. The proposed setup utilizes the long stopping ranges and the variable focal spot geometry of the high-energy uranium beams available at the GSI Helmholtzzentrum für Schwerionenforschung and Facility for Antiproton and Ion Research accelerator centers in Darmstadt, Germany. The release wave created by ion beams can be utilized to create a planar ramp loading of various samples. In such experiments, the predicted high pressure amplitudes (up to 10 Mbar) and short timescales of compression (<10 ns) will allow to test the time-dependent material deformation at unprecedented extreme conditions

M-Theory Model-Building and Proton Stability

We study the problem of baryon stability in M theory, starting from realistic four-dimensional string models constructed using the free-fermion formulation of the weakly-coupled heterotic string. Suitable variants of these models manifest an enhanced custodial gauge symmetry that forbids to all orders the appearance of dangerous dimension-five baryon-decay operators. We exhibit the underlying geometric (bosonic) interpretation of these models, which have a $Z_2 \times Z_2$ orbifold structure similar, but not identical, to the class of Calabi-Yau threefold compactifications of M and F theory investigated by Voisin and Borcea. A related generalization of their work may provide a solution to the problem of proton stability in M theory.Comment: 14 pages. Standard Late

Sum of Us: Strategyproof Selection from the Selectors

We consider directed graphs over a set of n agents, where an edge (i,j) is taken to mean that agent i supports or trusts agent j. Given such a graph and an integer k\leq n, we wish to select a subset of k agents that maximizes the sum of indegrees, i.e., a subset of k most popular or most trusted agents. At the same time we assume that each individual agent is only interested in being selected, and may misreport its outgoing edges to this end. This problem formulation captures realistic scenarios where agents choose among themselves, which can be found in the context of Internet search, social networks like Twitter, or reputation systems like Epinions. Our goal is to design mechanisms without payments that map each graph to a k-subset of agents to be selected and satisfy the following two constraints: strategyproofness, i.e., agents cannot benefit from misreporting their outgoing edges, and approximate optimality, i.e., the sum of indegrees of the selected subset of agents is always close to optimal. Our first main result is a surprising impossibility: for k \in {1,...,n-1}, no deterministic strategyproof mechanism can provide a finite approximation ratio. Our second main result is a randomized strategyproof mechanism with an approximation ratio that is bounded from above by four for any value of k, and approaches one as k grows

Understanding entanglement as resource: locally distinguishing unextendible product bases

It is known that the states in an unextendible product basis (UPB) cannot be distinguished perfectly when the parties are restricted to local operations and classical communication (LOCC). Previous discussions of such bases have left open the following question: What entanglement resources are necessary and/or sufficient for this task to be possible with LOCC? In this paper, I present protocols which use entanglement more efficiently than teleportation to distinguish certain classes of UPB's. The ideas underlying my approach to this problem offer rather general insight into why entanglement is useful for such tasks.Comment: Final, published version. Many revisions following very useful suggestions of the referee have been added. In particular, Appendix A has been completely rewritte

On the Complexity of Local Distributed Graph Problems

This paper is centered on the complexity of graph problems in the well-studied LOCAL model of distributed computing, introduced by Linial [FOCS '87]. It is widely known that for many of the classic distributed graph problems (including maximal independent set (MIS) and $(\Delta+1)$-vertex coloring), the randomized complexity is at most polylogarithmic in the size $n$ of the network, while the best deterministic complexity is typically $2^{O(\sqrt{\log n})}$. Understanding and narrowing down this exponential gap is considered to be one of the central long-standing open questions in the area of distributed graph algorithms. We investigate the problem by introducing a complexity-theoretic framework that allows us to shed some light on the role of randomness in the LOCAL model. We define the SLOCAL model as a sequential version of the LOCAL model. Our framework allows us to prove completeness results with respect to the class of problems which can be solved efficiently in the SLOCAL model, implying that if any of the complete problems can be solved deterministically in $\log^{O(1)} n$ rounds in the LOCAL model, we can deterministically solve all efficient SLOCAL-problems (including MIS and $(\Delta+1)$-coloring) in $\log^{O(1)} n$ rounds in the LOCAL model. We show that a rather rudimentary looking graph coloring problem is complete in the above sense: Color the nodes of a graph with colors red and blue such that each node of sufficiently large polylogarithmic degree has at least one neighbor of each color. The problem admits a trivial zero-round randomized solution. The result can be viewed as showing that the only obstacle to getting efficient determinstic algorithms in the LOCAL model is an efficient algorithm to approximately round fractional values into integer values

Contingent attentional engagement: stimulus- and goal-driven capture have qualitatively different consequences

We examined whether shifting attention to a location necessarily entails extracting the features at that location, a process referred to as attentional engagement. In three spatial-cuing experiments ( N = 60), we found that an onset cue captured attention both when it shared the target's color and when it did not. Yet the effects of the match between the response associated with the cued object's identity and the response associated with the target (compatibility effects), which are diagnostic of attentional engagement, were observed only with relevant-color onset cues. These findings demonstrate that stimulus- and goal-driven capture have qualitatively different consequences: Before attention is reoriented to the target, it is engaged to the location of the critical distractor following goal-driven capture but not stimulus-driven capture. The reported dissociation between attentional shifts and attentional engagement suggests that attention is best described as a camera: One can align its zoom lens without pressing the shutter button

Multiplexed DNA-Modified Electrodes

We report the use of silicon chips with 16 DNA-modified electrodes (DME chips) utilizing DNA-mediated charge transport for multiplexed detection of DNA and DNA-binding protein targets. Four DNA sequences were simultaneously distinguished on a single DME chip with 4-fold redundancy, including one incorporating a single base mismatch. These chips also enabled investigation of the sequence-specific activity of the restriction enzyme Alu1. DME chips supported dense DNA monolayer formation with high reproducibility, as confirmed by statistical comparison to commercially available rod electrodes. The working electrode areas on the chips were reduced to 10 μm in diameter, revealing microelectrode behavior that is beneficial for high sensitivity and rapid kinetic analysis. These results illustrate how DME chips facilitate sensitive and selective detection of DNA and DNA-binding protein targets in a robust and internally standardized multiplexed format

Attentional capture and engagement during the Attentional Blink: A “camera” metaphor of attention

Identification of a target is impaired when it follows a previous target within 500 ms, suggesting that our attentional system suffers from severe temporal limitations. Although control-disruption theories posit that such impairment, known as the attentional blink (AB), reflects a difficulty in matching incoming information with the current attentional set, disrupted-engagement theories propose that it reflects a delay in later processes leading to transient enhancement of potential targets. Here, we used a variant of the contingent-capture rapid serial visual presentation (RSVP) paradigm (Folk, Ester, & Troemel, 2009) to adjudicate these competing accounts. Our results show that a salient distractor that shares the target color captures attention to the same extent whether it appears within or outside the blink, thereby invalidating the notion that control over the attentional set is compromised during the blink. In addition, our results show that during the blink, not the attention-capturing object itself but the item immediately following it, is selected, indicating that the AB manifests as a delay between attentional capture and attentional engagement. We therefore conclude that attentional capture and attentional engagement can be dissociated as separate stages of attentional selection

Boolean versus continuous dynamics on simple two-gene modules

We investigate the dynamical behavior of simple modules composed of two genes with two or three regulating connections. Continuous dynamics for mRNA and protein concentrations is compared to a Boolean model for gene activity. Using a generalized method, we study within a single framework different continuous models and different types of regulatory functions, and establish conditions under which the system can display stable oscillations. These conditions concern the time scales, the degree of cooperativity of the regulating interactions, and the signs of the interactions. Not all models that show oscillations under Boolean dynamics can have oscillations under continuous dynamics, and vice versa.Comment: 8 pages, 10 figure