Reachability of the synchronous state in a mutually connected PLL network

Second-order phase locked loops (PLLs) are devices that are able to provide synchronization between the nodes in a network even under severe quality restrictions in the signal propagation. Consequently, they are widely used in telecommunication and control. Conventional master-slave (M-S) clock-distribution systems are being, replaced by mutually connected (MC) ones due to their good potential to be used in new types of application such as wireless sensor networks, distributed computation and communication systems. Here, by using an analytical reasoning, a nonlinear algebraic system of equations is proposed to establish the existence conditions for the synchronous state in an MC PLL network. Numerical experiments confirm the analytical results and provide ideas about how the network parameters affect the reachability of the synchronous state. The phase-difference oscillation amplitudes are related to the node parameters helping to design PLL neural networks. Furthermore, estimation of the acquisition time depending on the node parameters allows the performance evaluation of time distribution systems and neural networks based on phase-locked techniques. (c) 2008 Elsevier GmbH. All rights reserved.

The Cramer-Rao bound for initial conditions estimation of chaotic orbits

We derive the Cramer-Rao Lower Bound (CRLB) for the estimation of initial conditions of noise-embedded orbits produced by general one-dimensional maps. We relate this bound`s asymptotic behavior to the attractor`s Lyapunov number and show numerical examples. These results pave the way for more suitable choices for the chaotic signal generator in some chaotic digital communication systems. (c) 2006 Published by Elsevier Ltd.

Linear minimum mean square filter for discrete-time linear systems with Markov jumps and multiplicative noises

In this paper we obtain the linear minimum mean square estimator (LMMSE) for discrete-time linear systems subject to state and measurement multiplicative noises and Markov jumps on the parameters. It is assumed that the Markov chain is not available. By using geometric arguments we obtain a Kalman type filter conveniently implementable in a recurrence form. The stationary case is also studied and a proof for the convergence of the error covariance matrix of the LMMSE to a stationary value under the assumption of mean square stability of the system and ergodicity of the associated Markov chain is obtained. It is shown that there exists a unique positive semi-definite solution for the stationary Riccati-like filter equation and, moreover, this solution is the limit of the error covariance matrix of the LMMSE. The advantage of this scheme is that it is very easy to implement and all calculations can be performed offline. (c) 2011 Elsevier Ltd. All rights reserved.

Analysis of source-follower buffers implemented with graded-channel SOI nMOSFETs operating at cryogenic temperatures

This work studies the operation of source-follower buffers implemented with standard and graded-channel (GC) fully depleted (FD) SCI nMOSFETs at low temperatures. The analysis is performed by comparing the voltage gain of buffers implemented with GC and standard SOI nMOS transistors considering devices with the same mask channel length and same effective channel length. It is shown that the use of GC devices allows for achieving improved gain in all inversion levels in a wide range of temperatures. In addition, this improvement increases as temperature is reduced. It is shown that GC transistors can provide virtually constant gain, while for standard devices, the gain departs from the maximum value depending on the temperature and inversion level imposed by the bias current and input voltage. Two-dimensional numerical simulations were performed in order to study the reasons for the enhanced gain of GC MOSFETs at low temperatures. (C) 2009 Elsevier Ltd. All rights reserved.

Advantages of graded-channel SOI nMOSFETs for application as source-follower analog buffer

In this work the performance of graded-channel (CC) SOI MOSFETs operating as source-follower buffers is presented. The experimental analysis is performed by comparing the gain and linearity of buffers implemented with CC and standard SOI MOS devices considering the same mask dimensions. It is shown that by using CC devices, buffer gain very close to the theoretical limit can be achieved, with improved linearity, while for standard devices the gain departs from the theoretical value depending on the inversion level imposed by the bias current and input voltage. Two-dimensional numerical simulations were performed in order to confirm some hypotheses proposed to explain the gain behavior observed in the experimental data. By using numerical simulations the channel length has been varied, showing that the gain of buffers implemented with CC devices remains close to the theoretical limit even when short-channel devices are adopted. It has also been shown that the length of a source-follower buffer using CC devices can be reduced by a factor of 5, in comparison with a standard Sol MOSFET, without gain loss or linearity degradation. (C) 2008 Elsevier Ltd. All rights reserved.

Harmonic distortion analysis of double gate graded-channel MOSFETs operating in saturation

In this work we present an analysis of harmonic distortion (HD) in graded-channel (GC) gate-all-a round (GAA) devices operating in saturation region for analog applications. The study has been performed through device characterization and two-dimensional process and device simulations. The overall study has been done on the total and third order HDs. When applied in the saturation regime as an amplifier, the GC outperforms conventional GAA transistors presenting simultaneously higher transconductance, lower drain output conductance and more than 15 dB improved linearity. The influence of channel length reduction on the H D is also analyzed. Although slight linearity degradation is observed in both the conventional and the GC devices when reducing the channel length, the HD presented by the GC transistor is significantly lower than the one showed by conventional device for any Studied channel length. This allows AC input signal amplitude up to 20 times higher than the conventional GAA for a same specified distortion level. (C) 2008 Elsevier Ltd. All rights reserved.

Extensions of discrete triangular distributions and boundary bias in kernel estimation for discrete functions

Asymmetric discrete triangular distributions are introduced in order to extend the symmetric ones serving for discrete associated kernels in the nonparametric estimation for discrete functions. The extension from one to two orders around the mode provides a large family of discrete distributions having a finite support. Establishing a bridge between Dirac and discrete uniform distributions, some different shapes are also obtained and their properties are investigated. In particular, the mean and variance are pointed out. Applications to discrete kernel estimators are given with a solution to a boundary bias problem. (C) 2010 Elsevier B.V. All rights reserved.

Regression models for grouped survival data: Estimation and sensitivity analysis

In this study, regression models are evaluated for grouped survival data when the effect of censoring time is considered in the model and the regression structure is modeled through four link functions. The methodology for grouped survival data is based on life tables, and the times are grouped in k intervals so that ties are eliminated. Thus, the data modeling is performed by considering the discrete models of lifetime regression. The model parameters are estimated by using the maximum likelihood and jackknife methods. To detect influential observations in the proposed models, diagnostic measures based on case deletion, which are denominated global influence, and influence measures based on small perturbations in the data or in the model, referred to as local influence, are used. In addition to those measures, the local influence and the total influential estimate are also employed. Various simulation studies are performed and compared to the performance of the four link functions of the regression models for grouped survival data for different parameter settings, sample sizes and numbers of intervals. Finally, a data set is analyzed by using the proposed regression models. (C) 2010 Elsevier B.V. All rights reserved.

Large Woody Debris Input and Its Influence on Channel Structure in Agricultural Lands of Southeast Brazil

Riparian forests are important for the structure and functioning of stream ecosystems, providing structural components such as large woody debris (LWD). Changes in these forests will cause modifications in the LWD input to streams, affecting their structure. In order to assess the influence of riparian forests changes in LWD supply, 15 catchments (third and fourth order) with riparian forests at different conservation levels were selected for sampling. In each catchment we quantified the abundance, volume and diameter of LWD in stream channels; the number, area and volume of pools formed by LWD and basal area and tree diameter of riparian forest. We found that riparian forests were at a secondary successional stage with predominantly young trees (diameter at breast height < 10 cm) in all studied streams. Results showed that basal area and diameter of riparian forest differed between the stream groups (forested and non-forested), but tree density did not differ between groups. Differences were also observed in LWD abundance, volume, frequency of LWD pools with subunits and area and volume of LWD pools. LWD diameter, LWD that form pools diameter and frequency of LWD pools without subunits did not differ between stream groups. Regression analyses showed that LWD abundance and volume, and frequency of LWD pools (with and without subunits) were positively related with the proportion of riparian forest. LWD diameter was not correlated to riparian tree diameter. The frequency of LWD pools was correlated to the abundance and volume of LWD, but characteristics of these pools (area and volume) were not correlated to the diameter of LWD that formed the pools. These results show that alterations in riparian forest cause modifications in the LWD abundance and volume in the stream channel, affecting mainly the structural complexity of these ecosystems (reduction in the number and structural characteristics of LWD pools). Our results also demonstrate that riparian forest conservation actions must consider not only its extension, but also successional stage to guarantee the quantity and quality of LWD necessary to enable the structuring of stream channels.

Crop rotation in center-pivot for phytonematode control: density variation, pathogenicity and crop loss estimation

Crop rotation in center-pivot for phytonematode control: density variation, pathogenicity and crop loss estimation A field study conducted over three consecutive years, on a farm using crop rotation system under center-pivot and infested with the nematodes Pratylenchus brachyurus, P. zeae, Meloidogyne incognita, Paratrichodorus minor, Helicotylenchus dihystera, Mesocriconema ornata and M. onoense, demonstrated that intensive crop systems provide conditions for the maintenance of high densities of polyphagous phytonematodes. Of the crops established on the farm (cotton, maize, soybean and cowpea), cotton and soybean suffered the most severe crop losses, caused respectively by M. incognita and P. brachyurus. Since maize is a good host for both nematodes, but tolerant of M. incognita, its exclusion from cropping system would be favorable to the performance of cotton, soybean and cowpea. Results from experiments carried out in controlled conditions confirmed the pathogenicity of P. brachyurus on cotton. Additional management with genetic resistance was useful in fields infested with M. incognita, although the soybean performance was affected by low resistance of the cultivars used for P. brachyurus. In conclusion, crop rotation must be carefully planned in areas infested with polyphagous nematodes, specifically in the case of occurrence of two or more major pathogenic nematodes.

An integrated molecular map of yellow passion fruit based on simultaneous maximum-likelihood estimation of linkage and linkage phases

The development of genetic maps for auto-incompatible species, such as the yellow passion fruit (Passiflora edulis Sims f.flavicarpa Deg.) is restricted due to the unfeasibility of obtaining traditional mapping populations based on inbred lines. For this reason, yellow passion fruit linkage maps were generally constructed using a strategy known as two-way pseudo-testeross, based on monoparental dominant markers segregating in a 1:1 fashion. Due to the lack of information from these markers in one of the parents, two individual (parental) maps were obtained. However, integration of these maps is essential, and biparental markers can be used for such an operation. The objective of our study was to construct an integrated molecular map for a full-sib population of yellow passion fruit combining different loci configuration generated from amplified fragment length polymorphisms (AFLPs) and microsatellite markers and using a novel approach based on simultaneous maximum-likelihood estimation of linkage and linkage phases, specially designed for outcrossing species. Of the total number of loci, approximate to 76%, 21%, 0.7%, and 2.3% did segregate in 1:1, 3:1, 1:2:1, and 1:1:1:1 ratios, respectively. Ten linkage groups (LGs) were established with a logarithm of the odds (LOD) score >= 5.0 assuming a recombination fraction : <= 0.35. On average, 24 markers were assigned per LG, representing a total map length of 1687 cM, with a marker density of 6.9 cM. No markers were placed as accessories on the map as was done with previously constructed individual maps.

Sweet Basil (Ocimum basilicum) Extracts Obtained by Supercritical Fluid Extraction (SFE): Global Yields, Chemical Composition, Antioxidant Activity, and Estimation of the Cost of Manufacturing

In this work, supercritical technology was used to obtain extracts from Ocimum basilicum (sweet basil) with CO(2) and the cosolvent H(2)O at 1, 10, and 20% (w/w). The raw material was obtained from hydroponic cultivation. The extract`s global yield isotherms, chemical compositions, antioxidant activity, and cost of manufacturing were determined. The extraction assays were done for pressures of 10 to 30 MPa at 303 to 323 K. The identification of the compounds present in the extracts was made by GC-MS and ESI-MS. The antioxidant activity of extracts was determined using the coupled reaction of beta-carotene and linolenic acid. At 1% of cosolvent, the largest global yield was obtained at 10 MPa and 303 K (2%, dry basis-d.b.); at 10% of cosolvent the largest global yield was obtained at 10 and 15 MPa (11%, d.b.), and at 20% of cosolvent the largest global yield was detected at 30 MPa and 303 K (24%, d.b.). The main components identified in the extracts were eugenol, germacrene-D, epi-alpha-cadinol, malic acid, tartaric acid, ramnose, caffeic acid, quinic acid, kaempferol, caffeoylquinic acid, and kaempferol 3-O-glucoside. Sweet basil extracts exhibited high antioxidant activity compared to beta-carotene. Three types of SFE extracts from sweet basil were produced, for which the estimated cost of manufacturing (class 5 type) varied from US$ 47.96 to US$ 1,049.58 per kilogram of dry extract.

Estimating Amino Acid Requirement of Brazilian Freshwater Fish from Muscle Amino Acid Profile

Information on nutritional requirement of some Brazilian farmed fish species, especially essential amino acids (EAA) requirements, is scarce. The estimation of amino acids requirements based on amino acid composition of fish is a fast and reliable alternative. Matrinxa, Brycon amazonicus, and curimbata, Prochilodus lineatus, are two important Brazilian fish with potential for aquaculture. The objective of the present study was to estimate amino acid requirements of these species and analyze similarities among amino acid composition of different fish species by cluster analysis. To estimate amino acid requirement, the following formula was used: amino acid requirement = [(amount of an individual amino acid in fish muscle tissue) x (average totalEAA requirement among channel catfish, Ictalurus punctatus, Nile tilapia, Oreochromis niloticus, and common carp, Cyprinus carpio)]/(average fish muscle totalEAA). Most values found lie within the range of requirements determined for other omnivorous fish species, in exception of leucine requirement estimated for both species, and arginine requirement estimated for matrinxa alone. Rather than writing off the need for regular dose-response assays under the ideal protein concept to determine EAA requirements of curimbata and matrinxa, results set solid base for the study of tropical species dietary amino acids requirements.

Parameterization and Evaluation of Predictions of DSSAT/CANEGRO for Brazilian Sugarcane

The DSSAT/CANEGRO model was parameterized and its predictions evaluated using data from five sugarcane (Sacchetrum spp.) experiments conducted in southern Brazil. The data used are from two of the most important Brazilian cultivars. Some parameters whose values were either directly measured or considered to be well known were not adjusted. Ten of the 20 parameters were optimized using a Generalized Likelihood Uncertainty Estimation (GLUE) algorithm using the leave-one-out cross-validation technique. Model predictions were evaluated using measured data of leaf area index (LA!), stalk and aerial dry mass, sucrose content, and soil water content, using bias, root mean squared error (RMSE), modeling efficiency (Eff), correlation coefficient, and agreement index. The Decision Support System for Agrotechnology Transfer (DSSAT)/CANEGRO model simulated the sugarcane crop in southern Brazil well, using the parameterization reported here. The soil water content predictions were better for rainfed (mean RMSE = 0.122mm) than for irrigated treatment (mean RMSE = 0.214mm). Predictions were best for aerial dry mass (Eff = 0.850), followed by stalk dry mass (Eff = 0.765) and then sucrose mass (Eff = 0.170). Number of green leaves showed the worst fit (Eff = -2.300). The cross-validation technique permits using multiple datasets that would have limited use if used independently because of the heterogeneity of measures and measurement strategies.

Leaf area index estimation with MODIS reflectance time series and model inversion during full rotations of Eucalyptus plantations

The leaf area index (LAI) of fast-growing Eucalyptus plantations is highly dynamic both seasonally and interannually, and is spatially variable depending on pedo-climatic conditions. LAI is very important in determining the carbon and water balance of a stand, but is difficult to measure during a complete stand rotation and at large scales. Remote-sensing methods allowing the retrieval of LAI time series with accuracy and precision are therefore necessary. Here, we tested two methods for LAI estimation from MODIS 250m resolution red and near-infrared (NIR) reflectance time series. The first method involved the inversion of a coupled model of leaf reflectance and transmittance (PROSPECT4), soil reflectance (SOILSPECT) and canopy radiative transfer (4SAIL2). Model parameters other than the LAI were either fixed to measured constant values, or allowed to vary seasonally and/or with stand age according to trends observed in field measurements. The LAI was assumed to vary throughout the rotation following a series of alternately increasing and decreasing sigmoid curves. The parameters of each sigmoid curve that allowed the best fit of simulated canopy reflectance to MODIS red and NIR reflectance data were obtained by minimization techniques. The second method was based on a linear relationship between the LAI and values of the GEneralized Soil Adjusted Vegetation Index (GESAVI), which was calibrated using destructive LAI measurements made at two seasons, on Eucalyptus stands of different ages and productivity levels. The ability of each approach to reproduce field-measured LAI values was assessed, and uncertainty on results and parameter sensitivities were examined. Both methods offered a good fit between measured and estimated LAI (R(2) = 0.80 and R(2) = 0.62 for model inversion and GESAVI-based methods, respectively), but the GESAVI-based method overestimated the LAI at young ages. (C) 2010 Elsevier Inc. All rights reserved.