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Search Results: 1 - 10 of 242981 matches for " Richard R. Weber "
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Spike Correlations in a Songbird Agree with a Simple Markov Population Model
Andrea P Weber,Richard H. R Hahnloser
PLOS Computational Biology , 2007, DOI: 10.1371/journal.pcbi.0030249
Abstract: The relationships between neural activity at the single-cell and the population levels are of central importance for understanding neural codes. In many sensory systems, collective behaviors in large cell groups can be described by pairwise spike correlations. Here, we test whether in a highly specialized premotor system of songbirds, pairwise spike correlations themselves can be seen as a simple corollary of an underlying random process. We test hypotheses on connectivity and network dynamics in the motor pathway of zebra finches using a high-level population model that is independent of detailed single-neuron properties. We assume that neural population activity evolves along a finite set of states during singing, and that during sleep population activity randomly switches back and forth between song states and a single resting state. Individual spike trains are generated by associating with each of the population states a particular firing mode, such as bursting or tonic firing. With an overall modification of one or two simple control parameters, the Markov model is able to reproduce observed firing statistics and spike correlations in different neuron types and behavioral states. Our results suggest that song- and sleep-related firing patterns are identical on short time scales and result from random sampling of a unique underlying theme. The efficiency of our population model may apply also to other neural systems in which population hypotheses can be tested on recordings from small neuron groups.
Optimal Scheduling of Peer-to-Peer File Dissemination
Jochen Mundinger,Richard R. Weber,Gideon Weiss
Mathematics , 2006,
Abstract: Peer-to-peer (P2P) overlay networks such as BitTorrent and Avalanche are increasingly used for disseminating potentially large files from a server to many end users via the Internet. The key idea is to divide the file into many equally-sized parts and then let users download each part (or, for network coding based systems such as Avalanche, linear combinations of the parts) either from the server or from another user who has already downloaded it. However, their performance evaluation has typically been limited to comparing one system relative to another and typically been realized by means of simulation and measurements. In contrast, we provide an analytic performance analysis that is based on a new uplink-sharing version of the well-known broadcasting problem. Assuming equal upload capacities, we show that the minimal time to disseminate the file is the same as for the simultaneous send/receive version of the broadcasting problem. For general upload capacities, we provide a mixed integer linear program (MILP) solution and a complementary fluid limit solution. We thus provide a lower bound which can be used as a performance benchmark for any P2P file dissemination system. We also investigate the performance of a decentralized strategy, providing evidence that the performance of necessarily decentralized P2P file dissemination systems should be close to this bound and therefore that it is useful in practice.
The optimal strategy for symmetric rendezvous search on K3
Richard Weber
Mathematics , 2009,
Abstract: In the symmetric rendezvous search game played on Kn (the completely connected graph on n vertices) two players are initially placed at two distinct vertices (called locations). The game is played in discrete steps and at each step each player can either stay where he is or move to a different location. The players share no common labelling of the locations. They wish to minimize the expected number of steps until they first meet. Rendezvous search games of this type were first proposed by Steve Alpern in 1976. They are simple to describe, and have received considerable attention in the popular press as they model problems that are familiar in real life. They are notoriously difficult to analyse. Our solution of the symmetric rendezvous game on K3 makes this the first interesting game of its type to be solved, and establishes a 20 year old conjecture that the Anderson-Weber strategy is optimal.
The Anderson-Weber strategy is not optimal for symmetric rendezvous search on K4
Richard Weber
Mathematics , 2009,
Abstract: We consider the symmetric rendezvous search game on a complete graph of n locations. In 1990, Anderson and Weber proposed a strategy in which, over successive blocks of n-1 steps, the players independently choose either to stay at their initial location or to tour the other n-1 locations, with probabilities p and 1-p, respectively. Their strategy has been proved optimal for n=2 with p=1/2, and for n=3 with p=1/3. The proof for n=3 is very complicated and it has been difficult to guess what might be true for n>3. Anderson and Weber suspected that their strategy might not be optimal for n>3, but they had no particular reason to believe this and no one has been able to find anything better. This paper describes a strategy that is better than Anderson--Weber for n=4. However, it is better by only a tiny fraction of a percent.
Sesquicaesium hemisodium tetracyanidoplatinate(II) sesquihydrate
Andrew P. Weber,Milorad Stojanovic,Matthew R. Pischek,Richard E. Sykora
Acta Crystallographica Section E , 2010, DOI: 10.1107/s1600536810032551
Abstract: The title compound, Cs1.5Na0.5[Pt(CN)4]·1.5H2O, was isolated from solution as a salt. The tetracyanidoplatinate (TCP) anions are stacked in a linear quasi-one-dimensional arrangement along the b axis, with Pt...Pt interactions of 3.6321 (5) . The mixed alkali metal TCP contains three distinct alkali metal positions in the structure that do not show any mixed occupancy: Cs1 (site symmetry 2), Cs2 (general position) and Na1 (site symmetry overline{1}). The Na+ ion contains an octahedral coordination environment composed of two water molecules and four N-terminal cyanides, which serve to bridge TCP anions. The Cs+ cations contain mono- and bicapped square-prismatic environments, where the square prisms are formed from cyanide N atoms with water molecules capping the faces. The 1.5 water molecules per formula unit are a result of two fully occupied sites, one on a general position and one on a twofold rotation axis. Weak hydrogen-bonding interactions are observed between one water molecule and terminal N-atom acceptors from TCP, while the second water molecule is not involved in hydrogen bonding.
On the Sum-of-Squares Algorithm for Bin Packing
Janos Csirik,David S. Johnson,Claire Kenyon,James B. Orlin,Peter W. Shor,Richard R. Weber
Computer Science , 2002,
Abstract: In this paper we present a theoretical analysis of the deterministic on-line {\em Sum of Squares} algorithm ($SS$) for bin packing introduced and studied experimentally in \cite{CJK99}, along with several new variants. $SS$ is applicable to any instance of bin packing in which the bin capacity $B$ and item sizes $s(a)$ are integral (or can be scaled to be so), and runs in time $O(nB)$. It performs remarkably well from an average case point of view: For any discrete distribution in which the optimal expected waste is sublinear, $SS$ also has sublinear expected waste. For any discrete distribution where the optimal expected waste is bounded, $SS$ has expected waste at most $O(\log n)$. In addition, we discuss several interesting variants on $SS$, including a randomized $O(nB\log B)$-time on-line algorithm $SS^*$, based on $SS$, whose expected behavior is essentially optimal for all discrete distributions. Algorithm $SS^*$ also depends on a new linear-programming-based pseudopolynomial-time algorithm for solving the NP-hard problem of determining, given a discrete distribution $F$, just what is the growth rate for the optimal expected waste. This article is a greatly expanded version of the conference paper \cite{sumsq2000}.
Legal Assistance for Accused and Victims in Austrian Pre-Trial Criminal Proceedings  [PDF]
Alois Birklbauer, Richard Soyer, Christoph Weber
Beijing Law Review (BLR) , 2012, DOI: 10.4236/blr.2012.34027
Abstract: Based on two research projects this paper evaluates the legal assistance for accused and victims in pre-trial criminal proceedings in Austria after the implementation of a revised law on pre-trial proceedings in 2008. The research projects combined legal and empirical research. The project for scientific evaluation of the realization of the criminal procedure reform law (PEUS) analysed approx. 5000 pre-trial files and has additionally conducted 85 interviews with police officers, prosecutors, judges and lawyers. The results of the empirical research provide insight into which extent in practice in Austrian criminal proceedings the accused has access to legal advise. The paper comes to the conclusion that by strengthening victims’ access to legal representation in Austrian criminal proceedings in numerous cases the actual division of power to influence the proceedings has shifted from the accused to the victim.
A more general Pandora's rule?
Wojciech Olszewski,Richard Weber
Mathematics , 2015,
Abstract: In a classic model analysed by Weitzman an agent is presented with boxes containing prizes. She may open boxes in any order, discover prizes within, and optimally stop. She wishes to maximize the expected value of the greatest prize found, minus costs of opening boxes. The problem is solved by a so-called Pandora's rule, and has applications to searching for a house or job. However, this does not model the problem of a student who searches for the subject to choose as her major and benefits from all courses she takes while searching. So motivated, we ask whether there are any problems for which a generalized Pandora's rule is optimal when the objective is a more general function of all the discovered prizes. We show that if a generalized Pandora's rule is optimal for all specifications of costs and prize distributions, then the objective function must take a special form. We also explain how the Gittins index theorem can be applied to an equivalent multi-armed bandit problem to prove optimality of Pandora's rule for the student's problem. However, we also show that there do exist some problems which are not of multi-armed bandit type for which Pandora's rule is optimal.
Low-Dose High-Pitch CT Angiography of the Supraaortic Arteries Using Sinogram-Affirmed Iterative Reconstruction
Dietrich Beitzke, Richard Nolz, Sylvia Unterhumer, Christina Plank, Michael Weber, Rüdiger Schernthaner, Veronika Sch?pf, Florian Wolf, Christian Loewe
PLOS ONE , 2014, DOI: 10.1371/journal.pone.0099832
Abstract: Objective To prospectively evaluate image quality and radiation dose using a low-dose computed tomography angiography protocol and iterative image reconstruction for high-pitch dual-source CT-angiography (DSCTA) of the supraaortic arteries. Material and Methods DSCTA was performed in 42 patients, using either 120 kVp tube voltage, 120 mAS tube current, 2.4 pitch and filtered back projection, or 100 kVp tube voltage, 100 mAs tube current, 3.2 pitch, and sinogram affirmed iterative reconstruction. Measurements of vessel attenuation, of the contrast-to-noise ratio (CNR) and the signal-to-noise ratio (SNR) were performed to objectively evaluate image quality. Two readers evaluated subjective image quality and image noise, using a four-point scale. Effective dose was used to compare the differences in radiation dose. Results Low-dose protocol application showed significantly higher vessel opacification (p = 0.013), and non-significantly higher CNR and SNR values. There was no difference in the subjective image quality and image noise reading between the protocols. Effective dose was significantly lower using the low-dose protocol (1.29±0.21 mSv vs. 2.92±0.72 mSv; p<0.001). Conclusion The combined use of reduced tube voltage, reduced tube current, and iterative reconstruction reduces radiation dose by 55.4% in high-pitch DSCTA of the supraaortic arteries without impairment of image quality.
Multidisziplin res Management von Prostatakarzinom-Patienten. Interview mit Professor M. Montorsi
Weber R
Journal für Urologie und Urogyn?kologie , 2010,
Abstract:
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