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  • 1
    Publication Date: 2016-08-11
    Description: In this work, we present a simple algorithm to calculate automatically the Fourier spectrum of a Sinusoidal Pulse Width Modulation Signal (SPWM). Modulated voltage signals of this kind are used in industry by speed drives to vary the speed of alternating current motors while maintaining a smooth torque. Nevertheless, the SPWM technique produces undesired harmonics, which yield stator heating and power losses. By monitoring these signals without human interaction, it is possible to identify the harmonic content of SPWM signals in a fast and continuous manner. The algorithm is based in the autocorrelation function, commonly used in radar and voice signal processing. Taking advantage of the symmetry properties of the autocorrelation, the algorithm is capable of estimating half of the period of the fundamental frequency; thus, allowing one to estimate the necessary number of samples to produce an accurate Fourier spectrum. To deal with the loss of samples, i.e., the scan backlog, the algorithm iteratively acquires and trims the discrete sequence of samples until the required number of samples reaches a stable value. The simulation shows that the algorithm is not affected by either the magnitude of the switching pulses or the acquisition noise.
    Electronic ISSN: 2073-8994
    Topics: Mathematics , Physics
    Published by MDPI Publishing
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  • 2
    Publication Date: 2017-07-05
    Description: Along with being a dynamic process that affects large areas, desertification is also one of the most serious problems in many countries. The effects of this phenomenon threaten the sustainability of natural resources, namely water resources, agricultural production and major basic infrastructure, specifically roads and habitations. Several factors exacerbate this phenomenon such as the climate dryness, the geological and morphological characteristics of the terrain, the irrational use of space, population growth and the over-exploitation of vegetation and water resources. This work aims to evaluate the desertification index in the Oued-El-Maleh watershed, through the integration of key factors involved in the MEDALUS model (Mediterranean Desertification and Land Use) within a GIS. The model includes among its indexes: climate, vegetation, soil and management. Each index was obtained by the combination of sub-indexes. All the factors, measured and integrated into a geographic information system, enabled us to spatialize, on a synthetic map, the degree of the desertification effect throughout the watershed. This map is a managing tool available for decision-making regarding the selection of priority areas in the fight against desertification. High sensitivity to desertification class represents only 35% of the watershed. This class is concentrated in the north of the study area that corresponds to plains and low altitude. This could be explained by the dominance of agro-pastoral activity and the presence of a big population pressure.
    Electronic ISSN: 2076-3263
    Topics: Geosciences
    Published by MDPI Publishing
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  • 3
    Electronic Resource
    Electronic Resource
    New York : Wiley-Blackwell
    Journal of Polymer Science: Polymer Letters Edition 27 (1989), S. 433-436 
    ISSN: 0887-6258
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 30 (1992), S. 1407-1412 
    ISSN: 0887-624X
    Keywords: radiochemical grafting ; anion exchange membrane ; acid dialysis ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Using the preirradiation technique a kinetic study of the grafting of the 4-vinyl pyridine (V4P) and an aliphatic ammonium monomer (ALAM) onto the copolymer film of ethylene-tetrafluoroethylene (ETFE) has been performed. The influence of dose, temperature, and concentration of monomer, reticular agent, and inhibitor were investigated. The results are discussed on the basis of the interactions between monomer diffusibility and viscosity of the medium. The characteristics of some membranes were determined. Their applicability to the recovery of acid by dialysis is demonstrated.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Journal of High Resolution Chromatography 2 (1979), S. 45-47 
    ISSN: 0935-6304
    Keywords: Chromatography, theory ; Plate number calculation corrected for wide initial peaks ; Direct method of correction factor calculation ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Journal of High Resolution Chromatography 2 (1979), S. 93-94 
    ISSN: 0935-6304
    Keywords: Chromatography Theory peak shape, mathematical basis of real standard deviation and variances are much larger than “measured” ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Journal of High Resolution Chromatography 2 (1979), S. 164-171 
    ISSN: 0935-6304
    Keywords: Liquid chromatography, gradient technique ; Mobile phase composition programming by hardware construction ; Effluent composition curve analysis ; Numerical method for calculation and theory discussed ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The theory of gradient elution under hydrostatic equilibrium is developed for the case where only one reservoir and one mixing chamber are used and where both solvents have equal densities. Given the shapes of the two vessels, effluent concentration curve equations are deduced for different mixing chamber-reservoir combinations. On the other hand, given the equation for the effluent concentration curve, the reservoir cross-sectional area, as a function of height, can be deduced when the mixing chamber has a constant cross-section. The varying cross-section of the reservoir is accomplished by inserting thin discs of different areas on top of one another inside a regular vessel of constant cross-section.Except for complicated gradients, a given gradient can be accomplished using a reservoir with a cross-sectional area which varies linearly with height. In the case of complex gradients, a reservoir having two or more linear segments becomes necessary. A numerical method is given for the calculation of the continuously varying reservoir cross-section for the exact duplication of a given gradient.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
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  • 8
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Journal of High Resolution Chromatography 1 (1978), S. 257-262 
    ISSN: 0935-6304
    Keywords: Gas Chromatography ; Theory in qualitative analysis ; Retention index in isothermal and temperature programmed analysis (part 1) ; Simple dead volume calculations with three known compounds ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A definition for an absolute retention index is given. This index is independent of whether the process is isothermal or temperature programmed. The relation between this index and Kovats's index is discussed. General equations are derived for the retention times of homologous series, from which the position of the air peak or missing members can be determined. Methods used in the literature for air peak determination are improved and extended to other cases of interest. The retention index in temperature programmed chromatography is reexamined in the light of recent publications on temperature programming.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
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  • 9
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Journal of High Resolution Chromatography 3 (1980), S. 507-515 
    ISSN: 0935-6304
    Keywords: Constant volume Varigrad ; Hydrostatic Varigrad ; Incremental method of gradient elution ; Modified incremental method, advantages of Poisson distribution ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Different methods for producing a pre-assigned gradient in liquid chromatography are presented. A systematic approach to the calculations involved is given. The derived equations are mostly Poisson and Poisson summation distributions which are tabulated in the literature. The incremental method of gradient elution developed by Scott has been modified. In the modified apparatus two mixing chambers are used instead of one. This leads to an appreciable decrease in the number of reservoirs needed for the same precision in fitting a desired gradient. The application of the derived equations, together with other Varigrad modifications, will be given in Part 2 of this paper (to be published shortly in this Journal).
    Additional Material: 4 Ill.
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  • 10
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Journal of High Resolution Chromatography 5 (1982), S. 115-116 
    ISSN: 0935-6304
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
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