Alkylation of 1-azafagomine at the 2-N position was achieved by reductive amination of 1-N-acetyl... more Alkylation of 1-azafagomine at the 2-N position was achieved by reductive amination of 1-N-acetyl-3,4,6-tri-O-benzyl-1-azafagomine by using aldehydes, palladium hydroxide, and hydrogen in EtOAc/water/acetic acid followed by deprotection. The 2-N-butyl, hexyl, heptyl, nonyl, decyl, and 3-phenylpropyl derivatives were made in this manner, and were tested for inhibition of α-glucosidase from yeast, and of β-glucosidase from almonds. The new compounds were stronger β-glucosidase inhibitors than 1-azafagomine, but weaker α-glucosidase inhibitors.
The cover picture shows the glycosidase inhibitor 1-azafagomine binding to the enzyme β-glucosida... more The cover picture shows the glycosidase inhibitor 1-azafagomine binding to the enzyme β-glucosidase in the magnetic field of a solid-state NMR spectrometer. Details are discussed in the article by N. C. Nielsen, M. Bols et al. on p. 1735 ff.
In order to investigate the hypothesis that the glycosidase inhibitor isofagomine was bound to al... more In order to investigate the hypothesis that the glycosidase inhibitor isofagomine was bound to alpha- or beta-glucosidase in a 1,4B conformation, a number of bicyclic aziridines that adopt the 1,4B or B1,4 conformations were synthesised and investigated. (1R)-2-endo,3-exo-2,3-Dihydroxy-4-endo-4-hydroxymethyl-6- azabicyclo[3.1.0]hexane (5) and its N-methyl and N-benzyl analogues and (1S)-2-exo-3-endo-2,3-dihydroxy-4- endo-4-hydroxymethyl-6-azabicyclo-[3.1.0]hexane (6) were synthesised. The aziridines 5 and 6 were found to be weak or not inhibitors of alpha-glucosidase, beta-glucosidase and alpha-fucosidase.
A systematic method applied to design sliding mode surfaces is described. The design technique al... more A systematic method applied to design sliding mode surfaces is described. The design technique allows to find a simple surface for an specific desired dynamic response of the system. This design technique is specially interesting in tracking problems such as unity-power-factor rectifiers
This paper presents a new inverter topology based on a third-order quantum resonant converter. Th... more This paper presents a new inverter topology based on a third-order quantum resonant converter. The power stage consists of an input and output filter, a three-elements resonant network, and only three bi-directional switches which exhibit zero-current switching conditions. To control the switches, a closed-loop nonlinear control scheme is proposed in order to both achieve bi-directional power flow and make the
A novel design methodology of sliding mode control schemes for quantum resonant converters is pre... more A novel design methodology of sliding mode control schemes for quantum resonant converters is presented. The method is based on the imposition of a specified output-voltage dynamic response, and it provides a set of sliding surfaces guaranteeing high robustness and large-signal stability. Among these schemes, the final configuration is selected taking into account a simple practical implementation. Simulation and experimental results are reported, confirming the validity of the proposed solution
This paper presents a new switch control strategy for an electronic step-down transformer, provid... more This paper presents a new switch control strategy for an electronic step-down transformer, providing variable conversion ratio and zero-current switching conditions. To implement the new control technique, a closed-loop nonlinear controller is proposed, based on the sliding mode control theory. The controller provides good transient response, absence of steady-state errors in the output voltage and robust output response with respect
This paper presents multi-input sliding-mode control schemes for unity-power-factor rectifiers ba... more This paper presents multi-input sliding-mode control schemes for unity-power-factor rectifiers based on buck-boost converters. The proposed controllers can effectively improve the tracking performance of the line current and the output voltage regulation. The sliding surfaces are designed by imposing a desired dynamic behavior on the system, which allows us to determine the main parameters in designing the sliding-mode controller. This results in fast controllers which provide both robustness, with regard to external disturbances, and a good dynamic response of the output voltage
Phase locked loop (PLL) algorithms for grid synchronization are a very important part of the cont... more Phase locked loop (PLL) algorithms for grid synchronization are a very important part of the control in most of the grid-connected power converters applications. The performance of the PLL should not be much affected under distorted grid conditions: the presence of harmonics, unbalance, noise, etc in the inputs should not distort PLL measurements. This paper presents an optimized design approach of PLLs, both for single-phase and three-phase systems. The loop filter of the PLL sets its dynamic response; the loop filter should be tuned in order to achieve a correct tradeoff between transient response and harmonics/noise cancellation. This paper proposes the use of notch filters inside the loop in order to optimize the PLL performance; this approach is suitable both for single-phase and three-phase PLLs. Another novel interesting proposal of this paper is the implementation of the digitally controlled oscillator (DCO): the digital model of a sinusoidal oscillator is implemented, instead trigonometric functions. This reduces the needed digital resources without reducing the performance. This approach is specially useful for DSP-based control of power converters. The proposed PLLs have been implemented and tested in a fixed point DSP (TI TMS320LF2407) and also in a floating point microprocessor (PowerPC of the dSpace DS1103). The systems have been tested with different distorted inputs in order to check the validity of the design approaches and good results have been obtained.
In the practical design of a transmission cable, the characteristic impedance and the number of t... more In the practical design of a transmission cable, the characteristic impedance and the number of twists per meter in twisted cables are variables that are dependent on imperative conditions, with the disadvantage that these variables are strongly depending to each other. Cable manufacturing companies aim to provide customers' products with very well known physical characteristics. For this reason, a methodology to achieve accurate design of twisted pair cables based on the geometry of wires, before going to the manufacturing process is very desirable. In a previous paper, the deformations and irregularities that can occur in the twisted pair during the manufacturing process and their effects on the geometry of the twisted pair were studied by the authors. This paper describes an improved model for estimating the characteristic impedance of a twisted pair that allows an accurate electrical design. Two methods for a fast design of a cable, in agreement with the demanded specifications (characteristic impedance or number of twists per meter) are developed. Furthermore, a software program that automates all necessary calculations has been made. Thanks to the improved model, the design and production of a cable can be done faster, without the need of a big set of production samples. Results showed in this paper are a part of a larger research project carried out in association with the research and development department of a cable manufacturing company, and these results are being applied into the design department of this company.
Alkylation of 1-azafagomine at the 2-N position was achieved by reductive amination of 1-N-acetyl... more Alkylation of 1-azafagomine at the 2-N position was achieved by reductive amination of 1-N-acetyl-3,4,6-tri-O-benzyl-1-azafagomine by using aldehydes, palladium hydroxide, and hydrogen in EtOAc/water/acetic acid followed by deprotection. The 2-N-butyl, hexyl, heptyl, nonyl, decyl, and 3-phenylpropyl derivatives were made in this manner, and were tested for inhibition of α-glucosidase from yeast, and of β-glucosidase from almonds. The new compounds were stronger β-glucosidase inhibitors than 1-azafagomine, but weaker α-glucosidase inhibitors.
The cover picture shows the glycosidase inhibitor 1-azafagomine binding to the enzyme β-glucosida... more The cover picture shows the glycosidase inhibitor 1-azafagomine binding to the enzyme β-glucosidase in the magnetic field of a solid-state NMR spectrometer. Details are discussed in the article by N. C. Nielsen, M. Bols et al. on p. 1735 ff.
In order to investigate the hypothesis that the glycosidase inhibitor isofagomine was bound to al... more In order to investigate the hypothesis that the glycosidase inhibitor isofagomine was bound to alpha- or beta-glucosidase in a 1,4B conformation, a number of bicyclic aziridines that adopt the 1,4B or B1,4 conformations were synthesised and investigated. (1R)-2-endo,3-exo-2,3-Dihydroxy-4-endo-4-hydroxymethyl-6- azabicyclo[3.1.0]hexane (5) and its N-methyl and N-benzyl analogues and (1S)-2-exo-3-endo-2,3-dihydroxy-4- endo-4-hydroxymethyl-6-azabicyclo-[3.1.0]hexane (6) were synthesised. The aziridines 5 and 6 were found to be weak or not inhibitors of alpha-glucosidase, beta-glucosidase and alpha-fucosidase.
A systematic method applied to design sliding mode surfaces is described. The design technique al... more A systematic method applied to design sliding mode surfaces is described. The design technique allows to find a simple surface for an specific desired dynamic response of the system. This design technique is specially interesting in tracking problems such as unity-power-factor rectifiers
This paper presents a new inverter topology based on a third-order quantum resonant converter. Th... more This paper presents a new inverter topology based on a third-order quantum resonant converter. The power stage consists of an input and output filter, a three-elements resonant network, and only three bi-directional switches which exhibit zero-current switching conditions. To control the switches, a closed-loop nonlinear control scheme is proposed in order to both achieve bi-directional power flow and make the
A novel design methodology of sliding mode control schemes for quantum resonant converters is pre... more A novel design methodology of sliding mode control schemes for quantum resonant converters is presented. The method is based on the imposition of a specified output-voltage dynamic response, and it provides a set of sliding surfaces guaranteeing high robustness and large-signal stability. Among these schemes, the final configuration is selected taking into account a simple practical implementation. Simulation and experimental results are reported, confirming the validity of the proposed solution
This paper presents a new switch control strategy for an electronic step-down transformer, provid... more This paper presents a new switch control strategy for an electronic step-down transformer, providing variable conversion ratio and zero-current switching conditions. To implement the new control technique, a closed-loop nonlinear controller is proposed, based on the sliding mode control theory. The controller provides good transient response, absence of steady-state errors in the output voltage and robust output response with respect
This paper presents multi-input sliding-mode control schemes for unity-power-factor rectifiers ba... more This paper presents multi-input sliding-mode control schemes for unity-power-factor rectifiers based on buck-boost converters. The proposed controllers can effectively improve the tracking performance of the line current and the output voltage regulation. The sliding surfaces are designed by imposing a desired dynamic behavior on the system, which allows us to determine the main parameters in designing the sliding-mode controller. This results in fast controllers which provide both robustness, with regard to external disturbances, and a good dynamic response of the output voltage
Phase locked loop (PLL) algorithms for grid synchronization are a very important part of the cont... more Phase locked loop (PLL) algorithms for grid synchronization are a very important part of the control in most of the grid-connected power converters applications. The performance of the PLL should not be much affected under distorted grid conditions: the presence of harmonics, unbalance, noise, etc in the inputs should not distort PLL measurements. This paper presents an optimized design approach of PLLs, both for single-phase and three-phase systems. The loop filter of the PLL sets its dynamic response; the loop filter should be tuned in order to achieve a correct tradeoff between transient response and harmonics/noise cancellation. This paper proposes the use of notch filters inside the loop in order to optimize the PLL performance; this approach is suitable both for single-phase and three-phase PLLs. Another novel interesting proposal of this paper is the implementation of the digitally controlled oscillator (DCO): the digital model of a sinusoidal oscillator is implemented, instead trigonometric functions. This reduces the needed digital resources without reducing the performance. This approach is specially useful for DSP-based control of power converters. The proposed PLLs have been implemented and tested in a fixed point DSP (TI TMS320LF2407) and also in a floating point microprocessor (PowerPC of the dSpace DS1103). The systems have been tested with different distorted inputs in order to check the validity of the design approaches and good results have been obtained.
In the practical design of a transmission cable, the characteristic impedance and the number of t... more In the practical design of a transmission cable, the characteristic impedance and the number of twists per meter in twisted cables are variables that are dependent on imperative conditions, with the disadvantage that these variables are strongly depending to each other. Cable manufacturing companies aim to provide customers' products with very well known physical characteristics. For this reason, a methodology to achieve accurate design of twisted pair cables based on the geometry of wires, before going to the manufacturing process is very desirable. In a previous paper, the deformations and irregularities that can occur in the twisted pair during the manufacturing process and their effects on the geometry of the twisted pair were studied by the authors. This paper describes an improved model for estimating the characteristic impedance of a twisted pair that allows an accurate electrical design. Two methods for a fast design of a cable, in agreement with the demanded specifications (characteristic impedance or number of twists per meter) are developed. Furthermore, a software program that automates all necessary calculations has been made. Thanks to the improved model, the design and production of a cable can be done faster, without the need of a big set of production samples. Results showed in this paper are a part of a larger research project carried out in association with the research and development department of a cable manufacturing company, and these results are being applied into the design department of this company.
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