The infochemical core

Vocalizations, and less often gestures, have been the object of linguistic research for decades. However, the development of a general theory of communication with human language as a particular case requires a clear understanding of the organization of communication through other means. Infochemicals are chemical compounds that carry information and are employed by small organisms that cannot emit acoustic signals of an optimal frequency to achieve successful communication. Here, we investigate the distribution of infochemicals across species when they are ranked by their degree or the number of species with which they are associated (because they produce them or are sensitive to them). We evaluate the quality of the fit of different functions to the dependency between degree and rank by means of a penalty for the number of parameters of the function. Surprisingly, a double Zipf (a Zipf distribution with two regimes, each with a different exponent) is the model yielding the best fit although it is the function with the largest number of parameters. This suggests that the worldwide repertoire of infochemicals contains a core which is shared by many species and is reminiscent of the core vocabularies found for human language in dictionaries or large corpora.Peer ReviewedPostprint (author's final draft

Statistics for evaluating pre-post change: Relation between change in the distribution center and change in the individual scores

In a number of scientific fields, researchers need to assess whether a variable has changed between two time points. Average-based change statistics (ABC) such as Cohen's d or Hays' ω2 evaluate the change in the distributions' center, whereas Individual-based change statistics (IBC) such as the Standardized Individual Difference or the Reliable Change Index evaluate whether each case in the sample experienced a reliable change. Through an extensive simulation study we show that, contrary to what previous studies have speculated, ABC and IBC statistics are closely related. The relation can be assumed to be linear, and was found regardless of sample size, pre-post correlation, and shape of the scores' distribution, both in single group designs and in experimental designs with a control group. We encourage other researchers to use IBC statistics to evaluate their effect sizes because: (a) they allow the identification of cases that changed reliably; (b) they facilitate the interpretation and communication of results; and (c) they provide a straightforward evaluation of the magnitude of empirical effects while avoiding the problems of arbitrary general cutoffs.EE was supported by the scholarship FPI-UAM 2011 (granted by Universidad Autónoma de Madrid). The publication fee was partially supported by the Library of UC, Davi

SAMIE-LSQ: set-associative multiple-instruction entry load/store queue

The load/store queue (LSQ) is one of the most complex parts of contemporary processors. Its latency is critical for the processor performance and it is usually one of the processor hotspots. This paper presents a highly banked, set-associative, multiple-instruction entry LSQ (SAMIE-LSQ,) that achieves high performance with small energy requirements. The SAMIE-LSQ classifies the memory instructions (loads and stores) based on the address to be accessed, and groups those instructions accessing the same cache line in the same entry. Our approach relies on the fact that many in-flight memory instructions access the same cache lines. Each SAMIE-LSQ entry has space for several memory instructions accessing the same cache line. This arrangement has a number of advantages. First, it significantly reduces the address comparison activity needed for memory disambiguation since there are less addresses to be compared. It also reduces the activity in the data TLB, the cache tag and cache data arrays. This is achieved by caching the cache line location and address translation in the corresponding SAMIE-LSQ entry once the access of one of the instructions in an entry is performed, so instructions that share an entry can reuse the translation, avoid the tag check and get the data directly from the concrete cache way without checking the others. Besides, the delay of the proposed scheme is lower than that required by a conventional LSQ. We show that the SAMIE-LSQ saves 82% dynamic energy for the load/store queue, 42% for the LI data cache and 73% for the data TLB, with a negligible impact on performance (0.6%)Peer ReviewedPostprint (published version

Inherently workload-balanced clustered microarchitecture

The performance of clustered microarchitectures relies on steering schemes that try to find the best trade-off between workload balance and inter-cluster communication penalties. In previously proposed clustered processors, reducing communication penalties and balancing the workload are opposite targets, since improving one usually implies a detriment in the other. In this paper we propose a new clustered microarchitecture that can minimize communication penalties without compromising workload balance. The key idea is to arrange the clusters in a ring topology in such a way that results of one cluster can be forwarded to the neighbor cluster with a very short latency. In this way, minimizing communication penalties is favored when the producer of a value and its consumer are placed in adjacent clusters, which also favors workload balance. The proposed microarchitecture is shown to outperform a state-of-the-art clustered processor. For instance, for an 8-cluster configuration and just one fully pipelined unidirectional bus, 15% speedup is achieved on average for FP programs.Peer ReviewedPostprint (published version

Low-complexity distributed issue queue

As technology evolves, power density significantly increases and cooling systems become more complex and expensive. The issue logic is one of the processor hotspots and, at the same time, its latency is crucial for the processor performance. We present a low-complexity FP issue logic (MB/spl I.bar/distr) that achieves high performance with small energy requirements. The MB/spl I.bar/distr scheme is based on classifying instructions and dispatching them into a set of queues depending on their data dependences. These instructions are selected for issuing based on an estimation of when their operands will be available, so the conventional wakeup activity is not required. Additionally, the functional units are distributed across the different queues. The energy required by the proposed scheme is substantially lower than that required by a conventional issue design, even if the latter has the ability of waking-up only unready operands. MB/spl I.bar/distr scheme reduces the energy-delay product by 35% and the energy-delay product by 18% with respect to a state-of-the-art approach.Peer ReviewedPostprint (published version

A multivariate generalized independent factor GARCH model with an application to financial stock returns

We propose a new multivariate factor GARCH model, the GICA-GARCH model , where the data are assumed to be generated by a set of independent components (ICs). This model applies independent component analysis (ICA) to search the conditionally heteroskedastic latent factors. We will use two ICA approaches to estimate the ICs. The first one estimates the components maximizing their non-gaussianity, and the second one exploits the temporal structure of the data. After estimating the ICs, we fit an univariate GARCH model to the volatility of each IC. Thus, the GICA-GARCH reduces the complexity to estimate a multivariate GARCH model by transforming it into a small number of univariate volatility models. We report some simulation experiments to show the ability of ICA to discover leading factors in a multivariate vector of financial data. An empirical application to the Madrid stock market will be presented, where we compare the forecasting accuracy of the GICA-GARCH model versus the orthogonal GARCH one

A Note on the Pseudo-Spectra and the Pseudo-Covariance Generating Functions of ARMA Processes

Although the spectral analysis of stationary stochastic processes has solid mathematical foundations, this is not the case for non-stationary stochastic processes. In this paper, the algebraic foundations of the spectral analysis of non-stationary ARMA processes are established. For this purpose the Fourier Transform is extended to the field of fractions of polynomials. Then, the Extended Fourier Transform pair pseudo-covariance generating function / pseudo-spectrum, analogous to the Fourier Transform pair covariance generating function / spectrum,is defined. The new transform pair is well defined for stationary and non-stationary ARMA processes. This new approach can be viewed as an extension of the classical spectral analysis. It is shown that the frequency domain has some additional algebraic advantages over the time domain.

Bifurcation diagram for saddle/source bimodal linear dynamical systems

We continue the study of the structural stability and the bifurcations of planar bimodal linear dynamical systems (BLDS) (that is, systems consisting of two linear dynamics acting on each side of a straight line, assuming continuity along the separating line). Here, we enlarge the study of the bifurcation diagram of saddle/spiral BLDS to saddle/source BLDS and in particular we study the position of the homoclinic bifurcation with regard to the new improper node bifurcationPostprint (published version