307,777 research outputs found

    A Counterexample to Cover's 2P Conjecture on Gaussian Feedback Capacity

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    We provide a counterexample to Cover's conjecture that the feedback capacity CFBC_\textrm{FB} of an additive Gaussian noise channel under power constraint PP be no greater than the nonfeedback capacity CC of the same channel under power constraint 2P2P, i.e., CFB(P)C(2P)C_\textrm{FB}(P) \le C(2P).Comment: 2 pages, submitted to IEEE Transactions on Information Theor

    Farmers’ management of functional biodiversity goes beyond pest management in organic European apple orchards

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    Supporting functional biodiversity (FB), which provides natural pest regulation, is an environmentally sound and promising approach to reduce pesticide use in perennial cultures such as apple, especially in organic farming. However, little is known about farmers’ practices and motivations to implement techniques that favor FB, especially whether or not they really expect anything from FB in terms of pest regulation. In fact, FB-supporting techniques (FB-techniques) are massively questioned by practitioners due to inadequate information about their effectiveness. An interview survey was performed in eight European countries(i) to describe farmers’ practices and identify promising FB-techniques: (ii) to better understand their perceptions of and values associated with FB; and (iii) to identify potential drivers of (non-)adoption. Fifty-five advisors and 125 orchard managers with various degrees of experience and convictions about FB were interviewed and a total of 24 different FB-techniques which can be assigned to three different categories (ecological infrastructures, farming practices and redesign techniques) were described. Some were well-established measures (e.g., hedges and bird houses), while others were more marginal and more recent (e.g., animal introduction and compost). On average, farmers combined more than four techniques that had been implemented over a period of 13 years, especially during their establishment or conversion period. In general, it was difficult for farmers to evaluate the effectiveness of individual FB-techniques on pest regulation. They considered FB-techniques as a whole, targeting multiple species, and valued multiple ecosystem services in addition to pest regulation. The techniques implemented and their associated values differed among farmers who adopted various approaches towards FB. Three different approaches were defined: passive, active and integrated. Their appraisal of FB is even more complex because it may change with time and experience. These findings provide empirical evidence that the practical implementation of promising techniques remains a challenge, considering the diversity of situations and evaluation criteria. Increased cooperation between researchers, farmers and advisors should more effectively target research, advisory support and communication to meet farmers’ needs and perceptions

    Empirical Bayes and Full Bayes for Signal Estimation

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    We consider signals that follow a parametric distribution where the parameter values are unknown. To estimate such signals from noisy measurements in scalar channels, we study the empirical performance of an empirical Bayes (EB) approach and a full Bayes (FB) approach. We then apply EB and FB to solve compressed sensing (CS) signal estimation problems by successively denoising a scalar Gaussian channel within an approximate message passing (AMP) framework. Our numerical results show that FB achieves better performance than EB in scalar channel denoising problems when the signal dimension is small. In the CS setting, the signal dimension must be large enough for AMP to work well; for large signal dimensions, AMP has similar performance with FB and EB.Comment: This work was presented at the Information Theory and Application workshop (ITA), San Diego, CA, Feb. 201

    Diffusive capture processes for information search

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    We show how effectively the diffusive capture processes (DCP) on complex networks can be applied to information search in the networks. Numerical simulations show that our method generates only 2% of traffic compared with the most popular flooding-based query-packet-forwarding (FB) algorithm. We find that the average searching time, , of the our model is more scalable than another well known $n$-random walker model and comparable to the FB algorithm both on real Gnutella network and scale-free networks with $\gamma =2.4$. We also discuss the possible relationship between and , the second moment of the degree distribution of the networks

    Phenomenology of non-standard Z couplings in exclusive semileptonic b -> s transitions

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    The rare decays BK()+B\to K^{(*)}\ell^+\ell^-, BK()ννˉB\to K^{(*)}\nu\bar\nu and Bsμ+μB_s\to\mu^+\mu^- are analyzed in a generic scenario where New Physics effects enter predominantly via ZZ penguin contributions. We show that this possibility is well motivated on theoretical grounds, as the sˉbZ\bar sbZ vertex is particularly susceptible to non-standard dynamics. In addition, such a framework is also interesting phenomenologically since the sˉbZ\bar sbZ coupling is rather poorly constrained by present data. The characteristic features of this scenario for the relevant decay rates and distributions are investigated. We emphasize that both sign and magnitude of the forward-backward asymmetry of the decay leptons in BˉKˉ+\bar B\to \bar K^*\ell^+\ell^-, AFB(Bˉ){\cal A}^{(\bar B)}_{FB}, carry sensitive information on New Physics. The observable AFB(Bˉ)+AFB(B){\cal A}^{(\bar B)}_{FB}+{\cal A}^{(B)}_{FB} is proposed as a useful probe of non-standard CP violation in sˉbZ\bar sbZ couplings.Comment: Minor modifications; version to appear in Phys. Rev.

    Electrolytic lesions within central complex neuropils of the cockroach brain affect negotiation of barriers

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    Animals must negotiate obstacles in their path in order to successfully function within natural environments. These actions require transitions from walking to other behaviors, many of which are more involved than simple reflexes. For these behaviors to be successful, insects must evaluate objects in their path and then use that information to change posture or re-direct leg movements. Some of this control may occur within a region of the brain known as the central complex (CC). We used discrete electrolytic lesions to examine the role of certain sub-regions of the CC in various obstacle negotiation behaviors. We found that cockroaches with lesions to the protocerebral bridge (PB) and ellipsoid body (EB) exhibit abnormalities in turning and dealing with shelf-like objects; whereas, individuals with lesions to the fan-shaped body (FB) and lateral accessory lobe (LAL), exhibit abnormalities of those behaviors as well as climbing over blocks and up walls to a horizontal plane. Abnormalities in block climbing include decreased success rate, changes in climbing strategy, and delayed response to the block. Increases in these abnormal behaviors were significant in individuals with lesions to the FB and LAL. Although turning abnormalities are present in individuals with lesions to the LAL, EB and the lateral region of the FB, there are some differences in how these deficits present. For instance, the turning deficits seen in individuals with lateral FB lesions only occurred when turning in the direction opposite to the side of the brain on which the lesion occurred. By contrast, individuals with lesions to the EB and LAL exhibited turning abnormalities in both directions. Lesions in the medial region of the FB did not result in directional turning deficits, but in abnormalities in block climbing

    Sequential Necessary and Sufficient Conditions for Capacity Achieving Distributions of Channels with Memory and Feedback

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    We derive sequential necessary and sufficient conditions for any channel input conditional distribution P0,n{PXtXt1,Yt1: t=0,,n}{\cal P}_{0,n}\triangleq\{P_{X_t|X^{t-1},Y^{t-1}}:~t=0,\ldots,n\} to maximize the finite-time horizon directed information defined by CXnYnFBsupP0,nI(XnYn),   I(XnYn)=t=0nI(Xt;YtYt1)C^{FB}_{X^n \rightarrow Y^n} \triangleq \sup_{{\cal P}_{0,n}} I(X^n\rightarrow{Y^n}),~~~ I(X^n \rightarrow Y^n) =\sum_{t=0}^n{I}(X^t;Y_t|Y^{t-1}) for channel distributions {PYtYt1,Xt: t=0,,n}\{P_{Y_t|Y^{t-1},X_t}:~t=0,\ldots,n\} and {PYtYtMt1,Xt: t=0,,n}\{P_{Y_t|Y_{t-M}^{t-1},X_t}:~t=0,\ldots,n\}, where Yt{Y0,,Yt}Y^t\triangleq\{Y_0,\ldots,Y_t\} and Xt{X0,,Xt}X^t\triangleq\{X_0,\ldots,X_t\} are the channel input and output random processes, and MM is a finite nonnegative integer. \noi We apply the necessary and sufficient conditions to application examples of time-varying channels with memory and we derive recursive closed form expressions of the optimal distributions, which maximize the finite-time horizon directed information. Further, we derive the feedback capacity from the asymptotic properties of the optimal distributions by investigating the limit CXYFBlimn1n+1CXnYnFBC_{X^\infty \rightarrow Y^\infty}^{FB} \triangleq \lim_{n \longrightarrow \infty} \frac{1}{n+1} C_{X^n \rightarrow Y^n}^{FB} without any \'a priori assumptions, such as, stationarity, ergodicity or irreducibility of the channel distribution. The necessary and sufficient conditions can be easily extended to a variety of channels with memory, beyond the ones considered in this paper.Comment: 57 pages, 9 figures, part of the paper was accepted for publication in the proceedings of the IEEE International Symposium on Information Theory (ISIT), Barcelona, Spain 10-15 July, 2016 (Date of submission of the conference paper: 25/1/2016
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