Torque ripples in stepping motor driven systems

Stepping motor operation is characterized by torque ripples. In this paper it is shown these torque ripples are caused by both the stepping motor drive algorithms and the toothed construction of rotor and stator of the studied hybrid stepping motors. These torque ripples are analyzed, discussed and measured. The torque ripples are measured in the complete operating range of the motor and depicted in this paper for full- half- and micro-stepping. By doing this, the paper provides insight in the vibrating behavior of a stepping motor driven system and possible solutions to overcome this are placed in the right perspective

Efficient Synthesis of Novel BODIPY Dyes via C-H Functionalization

Boron dipyrromethenes are strongly colored solids that form intensely colored solutions with bright fluorescence upon irradiation and are better known by their trade name BODIPY. Over the last two decades these dyes have become an important class of fluorophores on account of their many excellent characteristics, as is evident from the numerous applications being reported for these dyes. Particularly their rich functionalization chemistry is a major reason for their attractiveness, as it allows a practically unlimited structural modification and hence provides a method to fine tune their chemical and physical properties. However, the traditional derivatization strategies are rather inefficient and/or require the manipulation of unstable intermediates. More efficient strategies to functionalize BODIPY dyes are based on C–H functionalization, allowing the introduction of the desired group in one reaction step. In this work, several C–H functionalization reactions were discovered and developed. Two different approaches to achieve functionalization of the C–H bond were explored. The first is based on transition metal catalyzed reactions involving C–H activation, the second strategy is based on radical reactions. The first developed reaction is a palladium catalyzed C–H arylation between a boron dipyrrin and a bromoarene at high temperatures. This arylation reaction affords 3-monoaryl and 3,5-diaryl dyes in moderate yields. A cross-dehydrogenative C–H arylation procedure between benzothiophene and BODIPY was also investigated, but could provide the desired product only in a low yield. A milder arylation protocol at room temperature was developed using a ferrocene catalyzed reduction of aryldiazonium salts in the presence of a boron dipyrromethene dye. This radical C–H arylation is a fast and high yielding reaction displaying a broad scope. By using this procedure both 3-monoaryl and 3,5-diaryl dyes can be synthesized. A second radical transformation that was developed uses oxidation of organoboranes, such as potassium trifluoroborate salts and boronic acids, in the presence of a BODIPY dye and provides a broad range of 3-monoalkylated fluorophores. By pushing the reaction at a higher temperature di-, tri- and tetraalkylated dyes can also be prepared. These novel protocols proved to be powerful synthetic tools for the preparation of a broad range of BODIPY derivatives. The utility of these reactions was demonstrated by synthesizing several sophisticated molecules, including asymmetrically substituted fluorophores, annulated chromophores and solid-emissive dyes.Acknowledgements Samenvatting Summary List of abbreviations Table of contents General introduction 1. Fluorescent organic dyes 2. Boron dipyrromethenes dyes 2.1. Fundamental properties 2.2. Discovery and structure 2.3. Synthesis of the BODIPY core 3. Synthesis of functionalized BODIPY derivatives 3.1. From suitably functionalized building blocks 3.2. By reacting BODIPY dyes 4. Influence of structural factors on the optical properties 5. Conclusion 6. References Goals and objectives Chapter 1. Direct palladium catalyzed C–H arylation of BODIPY dyes 1. Introduction 2. Optimization of the reaction 3. Scope of the reaction 4. Extension to multiple arylations 5. UV-vis spectroscopic properties 6. Conclusion 7. References Chapter 2. Oxidative transformations of BODIPY dyes 1. Introduction 2. Cross-dehydrogenative C–H arylation 3. Oxidative nucleophilic substitution of hydrogen with triethylamine 4. Oxidation of BODIPY in the synthesis of a new type of fluorophore 5. Conclusion 6. References Chapter 3. C–H functionalization of BODIPY dyes using radical chain reactions 1. Introduction 2. Reactivity of BODIPY towards radicals 3. Radical C–H methylation of BODIPY 4. Conclusion 5. References Chapter 4. Radical C–H arylation of BODIPY dyes using aryldiazonium salts 1. Introduction 2. Optimization of the reaction 3. Scope of the reaction 4. Applications 5. Aromatic amine as arylating reagent 6. UV-vis spectroscopic properties 7. Conclusion 8. References Chapter 5. Radical C–H alkylation of BODIPY dyes using potassium trifluoroborates or boronic acids 1. Introduction 2. Optimization of the reaction 3. Scope of the reaction 4. Extension to di-, tri- and tetraalkylation 5. Radical C-H alkylation using in situ generated trialkylboranes 6. UV-vis spectroscopic properties 7. Conclusion 8. References General conclusion and outlook 1. General conclusion 2. Future perspectives 3. References Experimental data 1. Synthetic procedures and characterization data from Chapter 1 2. Synthetic procedures and characterization data from Chapter 2 3. Synthetic procedures and characterization data from Chapter 3 4. Synthetic procedures and characterization data from Chapter 4 5. Synthetic procedures and characterization data from Chapter 5 6. Safety aspects 7. References List of publicationsnrpages: 222status: publishe

Two-Step Synthesis of Fluorescent 3-Arylated 1,3a,6a-Triazapentalenes via a Three-Component Triazolization Reaction

Novel 3-arylated 1,3a,6a-triazapentalenes were synthesized using a metal-free three-component triazolization reaction followed by a triflate based cyclization step. This method starts from simple commercial starting materials and provides an easy functionalization strategy for the 3-position of the triazapentalenes. By introducing electron-withdrawing groups onto this position, stable and highly fluorescent dyes could be synthesized.status: publishe

Postfunctionalization of the BODIPY Core: Synthesis and Spectroscopy

In this review we describe the various new methodologies for synthetic postmodification of the BODIPY core designed and developed by our research groups, as well as their electronic spectroscopic properties. We discuss the different strategies created for functionalization of the BODIPY framework at the pyrrole C-ring positions and the meso-position. Halogenated boron dipyrrins are substrates for nucleophilic substitution or Pd-catalyzed cross-coupling reactions. α-Unsubstituted BODIPYs can be functionalized with N and C nucleophiles through oxidative or vicarious nucleophilic substitution (VNS) of the α-hydrogen atoms. Combining this methodology with reversible Michael addition onto nitrostyrenes provides a route to 3-styrylated BODIPYs. Furthermore, the one-step, Pd-catalyzed C–H arylation of 3,5-unsubstituted BODIPYs leads to 3- and 3,5-arylated dyes. Finally, radical C–H arylation at the 3,5-positions of α-unsubstituted BODIPYs provides an additional synthesis route to arylated dyes.status: publishe

Learning generative models for active inference using tensor networks

Active inference provides a general framework for behavior and learning in autonomous agents. It states that an agent will attempt to minimize its variational free energy, defined in terms of beliefs over observations, internal states and policies. Traditionally, every aspect of a discrete active inference model must be specified by hand, i.e. by manually defining the hidden state space structure, as well as the required distributions such as likelihood and transition probabilities. Recently, efforts have been made to learn state space representations automatically from observations using deep neural networks. In this paper, we present a novel approach of learning state spaces using quantum physics-inspired tensor networks. The ability of tensor networks to represent the probabilistic nature of quantum states as well as to reduce large state spaces makes tensor networks a natural candidate for active inference. We show how tensor networks can be used as a generative model for sequential data. Furthermore, we show how one can obtain beliefs from such a generative model and how an active inference agent can use these to compute the expected free energy. Finally, we demonstrate our method on the classic T-maze environment

Planning with tensor networks based on active inference

Tensor networks (TNs) have seen an increase in applications in recent years. While they were originally developed to model many-body quantum systems, their usage has expanded into the field of machine learning. This work adds to the growing range of applications by focusing on planning by combining the generative modeling capabilities of matrix product states and the action selection algorithm provided by active inference. Their ability to deal with the curse of dimensionality, to represent probability distributions, and to dynamically discover hidden variables make matrix product states specifically an interesting choice to use as the generative model in active inference, which relies on 'beliefs' about hidden states within an environment. We evaluate our method on the T-maze and Frozen Lake environments, and show that the TN-based agent acts Bayes optimally as expected under active inference

Direct palladium-catalysed C–H arylation of BODIPY dyes at the 3- and 3,5-positions

A new one-step synthetic method towards 3- and 3,5-arylated BODIPY dyes via palladium-catalysed C–H arylation has been developed and its scope has been investigated.status: publishe