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Showing papers by "Simón Bolívar University published in 1979"


Journal ArticleDOI
01 Aug 1979
TL;DR: It is shown that the linear equalizer is in fact a portion of the D FE receiver and that the processing done by the DFE is exactly equivalent to the general problem of linear prediction.
Abstract: As real world communication channels are stressed with higher data rates, intersymbol interference (ISI) becomes a dominant limiting factor. One way to combat this effect that has recently received considerable attention is the use of a decision feedback equalizer (DFE) in the receiver. The action of the DFE is to feed back a weighted sum of past decision to cancel the ISI they cause in the present signaling interval. This paper summarizes the work in this area beginning with the linear equalizer. Three performance criteria have been used to derive optimum systems; 1) minimize the noise variance under a "zero forcing" (ZF) constraint i.e., insist that all intersymbol interference is cancelled, 2) minimize the mean-square error (MMSE) between the true sample and the observed signal just prior to the decision threshold, and 3) minimize the probability of error (Min P e ). The transmitter can be fixed and the receiver optimized or one can obtain the joint optimum transmitter and receiver. The number of past decisions used in the feedback equalization can be finite or infinite. The infinite case is easier to handle analytically. In addition to reviewing the work done in the area, we show that the linear equalizer is in fact a portion of the DFE receiver and that the processing done by the DFE is exactly equivalent to the general problem of linear prediction. Other similarities in the various system structures are also shown. The effect of error propagation due to incorrect decisions is discussed, and the coaxial cable channel is used as an example to demonstrate the improvement available using DFE.

501 citations


Journal ArticleDOI
TL;DR: In this paper, Bertini theorems for hypersurface sections containing a subscheme are given for the case of hypersurfaces containing a single subspace and a single component.
Abstract: (1979). Bertini theorems for hypersurface sections containing a subscheme. Communications in Algebra: Vol. 7, No. 8, pp. 775-790.

153 citations


Journal ArticleDOI
TL;DR: The time-varying shape of the induced depression is calculated as a function of the power distribution in the laser beam and of the thermal and mechanical properties of the material.
Abstract: Heavy hydrocarbons are irradiated with a Gaussian laser beam. The time-varying temperature distribution induced in the fluid gives rise to a surface-tension distribution. The later gives rise in turn to an accompanying liquid flow and surface-height distribution. In this paper, the time-varying shape of the induced depression is calculated as a function of the power distribution in the laser beam and of the thermal and mechanical properties of the material. The intensity distribution in the laser beam reflected from the depression is also calculated. Good agreement is found with previous experimental results.

58 citations


Journal ArticleDOI
TL;DR: Adaptive strategies in two plants of Venezuelan páramos (alpine areas): the widely distributed, caulescent, and pubescent Espeletia schultzii Wedd.
Abstract: We compared adaptive strategies in two plants of Venezuelan paramos (alpine areas): the widely distributed, caulescent, and pubescent Espeletia schultzii Wedd. with the acaulescent, nearly glabrous E. atropurpurea A.C. Smith which is restricted to mesic sites just above treeline. Both species occur together at 3,450 m, near treeline. Physiologically, E. schultzii was more drought resistant than E. atropurpurea, and was better adapted for carbon dioxide fixation under low temperatures. The densely pubescent leaves of E. schultzii are highly reflective; this increases the intensity of light needed for photosynthetic saturation and influences leaf temperature. Leaf pubescence may reduce the level of insect predation. Measurements of leaf productivity indicate higher values for E. atropurpurea during the rainy season and higher values for E. schultzii during the dry season. However, annual values of leaf productivity are similar for both species. Benefits of specialization in E. atropurpurea include reduced costs for stem and leaf hair production, higher growth rates during the rainy season and the ability to grow beneath canopies of some larger arborescent species. Costs of specialization include lower growth rates during the dry season, great susceptibility to insect predation and restriction to low elevation, mesic sites.

29 citations


Journal ArticleDOI
01 Jul 1979-Genetica
TL;DR: Spiny rats from Venezuela show an extensive karyotypic diversification (2n=24 to 2n=62) and little morphological differentiation and genetic distance, heterozygosity and polymorphism based upon 22 loci in semispecies and allospecies of the Proechimys guairae superspecies from N Central Venezuela are reported.
Abstract: Spiny rats from Venezuela show an extensive karyotypic diversification (2n=24 to 2n=62) and little morphological differentiation. This study reports genetic distance, heterozygosity and polymorphism based upon 22 loci in semispecies and allospecies of the Proechimys guairae superspecies from N Central Venezuela, as compared with Proechimys urichi, a member of the Proechimys trinitatis superspecies from eastern Venezuela. Four chromosome forms of the P. guairae complex are included, each characterized by karyotypes of 2n=46 (Fundamental Number=72), 2n=48 (FN=72), 2n=50 (FN=72) and 2n=62 (FN=74). Proechimys urichi has a distinetive karyotype of 2n=62 (FN=88). The overall mean value of Nei's genetic identity index for all pair-wise comparisons is I=0.942±0.011. Mean identity within the P. guairae complex is Ī=0.969±0.033. Mean identity between P. urichi and members of that complex is Ī=0.889±0.011. Within the P. guairae complex, increased genetic divergence is correlated with higher karyotypic divergence. Heterozygosity varies from H=0.059 to H=0.153, with a mean value of H0.059. The mean percent of polymorphic loci is P=18.2±3.9 after the ‘0,95%’ polymorphism criterion, and P=20,5±5.2 after the ‘0.99%’ criterion. These results are compared with similar data from fossorial and non-fossorial rodents. Spiny rats are non-fossorial, forest-dwelling rodents which have undergone a speciation process with little genetic divergence and extensive chromosome rearrangements.

25 citations


Journal ArticleDOI
TL;DR: In this article, a model was developed to represent the continuous sterilization of Bingham plastic fluid foods for the laminar, isoviscous and nonisoviscus flow, with applications to design.
Abstract: A model was developed to represent the continuous sterilization of Bingham plastic fluid foods for the laminar, isoviscous and nonisoviscous flow, with applications to design. The length of the heating and cooling sections as well as nutrient retention were numerically calculated for a required sterilization value. Thiamine and C. botulinum were considered for this purpose. There was a considerable difference between solutions obtained for isoviscous and nonisoviscous flow. Therefore, it would not be advisable to overlook the temperature effect on rheological fluid properties. Optimal nutrient retention was shown to occur for the smallest tube diameter studied.

10 citations


Journal ArticleDOI
TL;DR: In this paper, a reduced nonconstrained Lagrangian of electromagnetism including monopoles is presented and the Cabibbo-Ferrari formulation is studied in the infinite-momentum frame.
Abstract: A reduced nonconstrained Lagrangian of electromagnetism including monopoles is presented. The Lagrangian depends on two degrees of freedom and is invariant under dual rotations. The Cabibbo-Ferrari formulation is studied in the infinite-momentum frame. We prove that the Lagrangian formulation of the Cabibbo-Ferrari theory has four degrees of freedom. Nevertheless, the physical observables depend on only two linear combinations of the four degrees of freedom. The mixing-gauge transformations may be clearly understood by writing them in terms of two arbitrary scalar solutions of the massless Klein-Gordon equation.

6 citations


Journal ArticleDOI
TL;DR: In this article, the necessary and sufficient conditions for a coherent state to remain coherent are discussed and the condizioni necessarie e sufficienti perché uno stato coerente rimanga coerenti are discussed.
Abstract: SummaryNecessary and sufficient conditions for a coherent state to remain coherent are discussed.RiassuntoSi discutono le condizioni necessarie e sufficienti perché uno stato coerente rimanga coerente.РезюмеОбсуждаются необходимое и достаточное условие, чтобы когерентное состояние оставалось бы когерентным.

5 citations


Book ChapterDOI
01 Jan 1979
TL;DR: This chapter describes a few recent developments in stability of general systems and describes the existence of continuous and semicontinuous and Liap unov and para-Liapunov functions.
Abstract: Publisher Summary This chapter describes a few recent developments in stability of general systems. A difficulty that easily arises in an attempt to establish a unified theory is the great number of possible stability concepts with all the complexities this entails. The chapter discusses the existence of Liapunov-type functions. The chapter highlights this problem at various levels. The chapter describes the existence of continuous and semicontinuous and Liapunov and para-Liapunov functions. The difference of behavior with respect to existence of autonomous and nonautonomous Liapunov functions also finds its natural explanation in this context.

5 citations


Journal ArticleDOI
TL;DR: In this paper, the magnitude of the localized magnetic moment of a transition or rare earth element impurity in a metal is evaluated within the framework of the Anderson model, where rotational invariance is preserved throughout.
Abstract: The magnitude of the localized magnetic moment of a transition or rare earth element impurity in a metal is evaluated within the framework of the Anderson model. Rotational invariance is preserved throughout. Graphs of the magnitude of the magnetization as a function of the relevant darameters of the model are provided and discussed. La magnitude du moment magnetique localise d'une impurete de un metal de transition ou de terres rares est evalue dans le contexte du model d'Anderson. Invariance rotationelle est preservee partout. Graphes de la magnitude de la magnetisation comme fonction des parametres apropries du model sont presentes et discutes.

3 citations


Journal ArticleDOI
TL;DR: In this paper, the Baker-Campbell-Hausdorff formula for the chiral SU(2) supergroup was used to give the finite form of each element of this group in terms of the local fields emering in the infinitesimal real superscalar generator.
Abstract: In the theory of supersymmetricSU(2) Yang-Mills fields described on the 8th dimensional superspace, the local gauge transformations constitute a group whose Lie algebra has as coefficients belonging to the Weyl-spinorial Grassmann algebra. We present here a Baker-Campbell-Hausdorff formula for the chiralSU(2) supergroup and using this formula we give the finite form of each element of this group in terms of the local fields emering in the infinitesimal real superscalar generator.

Journal ArticleDOI
TL;DR: In this article, the probability density p of a plane Brownian motion stopped by a two-sided constant barrier is shown to be a solution of a Kolmogorov forward equation of the form ℒ*p=0.
Abstract: The probability density p of a plane Brownian motion stopped by a two-sided constant barrier is shown to be a solution of a Kolmogorov forward equation of the form ℒ* p=0. The operator ℒ* is the product of two second order differential operators, each of them corresponding to a related one-dimensional Brownian motion.

Journal ArticleDOI
TL;DR: In this paper, the authors calculate the line shape of the optical absorption in an antiferromagnetic ground state of a half-filled extended Hubbard chain and find that the line is asymmetric and a bound excitonic state always occurs for a narrow band (2 t ⩽ V ⪡ U ).

Proceedings ArticleDOI
27 Jul 1979
TL;DR: In this paper, the physical properties of laser-irradiated heavy hydrocarbons are investigated and a photographic sequence of this phenomenon (taken at 64 frames/sec) is presented.
Abstract: Basic research on physical properties of laser-irradiated heavy hydrocarbons is being conducted in order to support technological research in this field. For low power-concentrations, laser-induced thermocapillary flow is the dominant phenomenon. Experimental results and the corresponding theory are presented. Temperature-dependence of the surface tension gives rise to the formation of a surface depression, whose shape is studied as a function of time. Direct photo graphs of the laser wave reflected from the deformed surface are actually holograms of the later. Reconstructed images are presented. For higher power concentrations evaporation of the sample takes place. A photographic sequence of this phenomenon (taken at 64 frames/sec) is presented.© (1979) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.


Proceedings ArticleDOI
27 Jul 1979
TL;DR: Speckle metrological techniques developed in the last three years for Transient Phenomena Analysis are reviewed in this article, where applications include: a)transient deformations of solid propellants, Odisplacements of petroleum samples, and transmission of speckle patterns by a TV chain.
Abstract: Speckle Metrological techniques developed in the last three years for Transient Phenomena Analysis are reviewed. Applications include: a)transient deformations of solid propellants, Odisplacements of petroleum samples, and c)transmission of speckle patterns by a TV chain.© (1979) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.