Multi-parameter structural transformations of passive electrical networks and natural frequency assignment

The paper examines the problem of systems redesign within the context of passive electrical networks by considering the problem of multi-parameter changes, their representation and impact on properties such as characteristic frequencies. The general problem area is the modelling of systems, whose structure is not fixed but evolves during the system lifecycle. The specific problem we are addressing is the study of effect of changing the topology of an electrical network that is changing individual elements of the network into elements of different type and value, augmenting / or eliminating parts of the network and developing a framework that allows the study of the effect of such transformations on the natural frequencies. This problem is a special case of the more general network redesign problem. We use the Impedance-Admittance models and we establish a representation of the different types of transformations on such models. For the case of network cardinality preserving transformations, we formulate the natural frequencies assignment problem as a problem of zero assignment of matrix pencils by additive structured transformations and this allows the deployment of the Determinantal Assignment Problem framework for the study of assignment and determination of fixed natural frequencies

System Properties of Implicit Passive Electrical Networks Descriptions

Redesigning systems by changing elements, topology, organization, augmenting the system by the addition of subsystems, or removing parts, is a major challenge for systems and control theory. A special case is the redesign of passive electric networks which aims to change the natural dynamics of the network (natural frequencies) by the above operations leading to a modification of the network. This requires changing the system to achieve the desirable natural frequencies and involves the selection of alternative values for dynamic elements and non-dynamic elements within a fixed interconnection topology and/or alteration of the interconnection topology and possible evolution of the network (increase of elements, branches). The use of state-space or transfer function models does not provide a suitable framework for the study of this problem, since every time such changes are introduced, a new state space or transfer function model has to be recalculated. The use of impedance and admittance modeling, provides a suitable framework for the study of network properties under the process of re-engineering transformations. This paper deals with the fundamental system properties of the impedance-admittance network description which provide the appropriate framework for network re-engineering. We identify the natural topologies expressing the structured transformations linked to the impedance-graph, admittance graph-topology of the network and examine issues such as network regularity, number of finite frequencies and provide characterization of them in terms of the basic network matrices. The implicit network representation introduced provides a natural framework for expressing the different types of re-engineering transformations which can be used for the study of the natural frequencies assignment

Matrix pencil representation of structural transformations of passive electrical networks

The paper examines the problem of systems redesign within the context of passive electrical networks by considering the problem of multi-parameter and topology changes, and their representation. This representation may be used to investigate the impact of such changes on properties such as characteristic frequencies. The general problem area is the modelling of systems, whose structure is not fixed but evolves during the system life-cycle. The specific problem we are addressing is the study of effect of changing the topology of an electrical network that is changing individual elements of the network into elements of different type and value, augmenting / or eliminating parts of the network and developing a framework that allows the study of the effect of such transformations on the natural frequencies. This problem is a special case of the more general network redesign problem. We use the Impedance-Admittance models and we establish a representation of the different types of transformations on such models. The representation of the structural transformations is given in terms of the companion pencil that preserves the natural topologies of the RLC network

Implicit network descriptions of RLC networks and the problem of re-engineering

The thesis deals with aspects of Systems Re-engineering specialised to the case of passive electrical networks. Re-engineering is a problem different from traditional control problems and this emerges when it is realised that the systems designed in the past cannot perform according to the new performance requirements and such performance cannot be improved by traditional control activities. Re-engineering implies that we intervene in early stages of system design involving sub-processes, values of physical elements, interconnection topology, selection of systems of inputs and outputs and of course retuning of control structures. This is a very challenging problem which has not been addressed before in a systematic way and needs fundamental new thinking, based on understanding of structure evolution during the stages of integrated design. A major challenge in the study of this problem is to have a system representation that allows study of evolution of system properties as well as structural invariants. For linear systems the traditional system representations, such as transfer functions, state space models and polynomial type models do not provide a suitable framework for study structure and property evolutions, since for every change we need to compute again these models and the transformations we have used do not appear in an explicit form in such models. It is for this reason, for a general system, such system representations are not suitable for study of system representations on re-engineering. It has been recognized that for the special family of systems defined by the passive electrical networks (RLC), there exists a representation introduced by the loop/ nodal analysis, expressed by the impedance/admittance integral-differential models, which have the property of re-engineering transformations of the following type: 1. Changing the values or possible nature of existing elements without changing the network topology, 2. Modifying the network topology without changing network cardinality, that is number of independent loops or nodes, 3. Augmenting or reducing the network by addition or deletion of sub-networks, 4. Combination of all the above transformations. These kinds of transformations may be represented as perturbations on the original impedance/admittance models. The above indicates that impedance/admittance integral-differential models, which from now on will be referred to as Implicit Network Descriptions is the natural vehicle for studying re-engineering on electrical networks. Although issues related to realisation of impedance/admittance transfer functions within RLC topologies, has been the topic of classical network synthesis, the system aspects of such descriptions have not been properly considered. Addressing problems of network re-engineering requires the development of the fundamental system aspects of such new descriptions in terms of McMillan degree, regularity and a number of other properties. Certain problems of evolution (of system properties) are linked to Frequency Assignment, as far as natural frequencies under re-engineering and this requires use of techniques developed within control theory for Frequency Assignment Problems

Partially Fixed Structure Determinantal Assignment Problems

In this article, we deal with the study of the determinantal assignment problem (DAP) when the parameters of the compensator are not entirely free, but some of them are fixed. The problem is reduced to a restricted form of an exterior algebra problem (decomposability of multivectors), which is referred to as partial decomposability problem. We study this problem and in case that this problem has no solution, we examine the problem of approximate partial decomposability. We treat the problem of exact or partial decomposability into a vector and a multivector of lower dimension. If this procedure is repeated then this results in an approximation of the initial multivector into a decomposable vector. The approximation of a vector by an optimal decomposable multivector is a nonlinear procedure and has been solved completely using the power method. The method developed in this article, although it produces a suboptimal solution, can be used alternatively for the solution of DAP or the approximate DAP, as a shorter and easier approach, because it is based on known tools as the singular value decomposition. We apply these results to treat the restricted approximate decomposability problem, which leads to approximate solutions to the pole placement and zero assignment problems

Orientation of Implicit State Space Models and the Partitioning of Kronecker Structure

Early stages modelling of processes involves issues of classification of variables into inputs, outputs and internal variables, referred to as Model Orientation Problem (MOP) which may be addressed on state space implicit, or matrix pencil descriptions. Defining orientation is equivalent to producing state space models of the regular or singular type. In this paper we consider autonomous differential descriptions defined by matrix pencils and then search for strict equivalence transformations which introduce the partitioning of the implicit vector into states and possible inputs and outputs, referred to as system orientation. The Kronecker invariant structure of the matrix pencil description is shown to be central to the solution of system orientation and this is expressed as a problem of classification and partitioning of the Kronecker invariants. It is shown that the types of Kronecker invariants characterise the nature of the system orientation solutions. Studying the conditions, under which such oriented models may be derived, as well as their structural properties in terms of the Kronecker structure, is the issue considered here

Reengineering of interbank networks

We investigate the reengineeering of interbank networks with a specific focus on capital increase. We consider a scenario where all other components of the network’s infrastructure remain stable (a practical assumption for short-term situations). Our objective is to assess the impact of raising capital on the network’s robustness and to address the following key aspects. First, given a predefined target for network robustness, our aim is to achieve this goal optimally, minimizing the required capital increase. Second, in cases where a total capital increase has been determined, the central challenge lies in distributing this increase among the banks in a manner that maximizes the stability of the network. To tackle these challenges, we begin by developing a comprehensive theoretical framework. Subsequently, we formulate an optimization model for the network’s redesign. Finally, we apply this framework to practical examples, highlighting its applicability in real-world scenarios

Bioclimatic rehabilitation of an open market place by a computational fluid dynamics simulation assessment

These days urban design of open spaces is strongly related to bioclimatic techniques and practices. It is here presented the procedure of a bioclimatic study by the use of simulation tools. The area of an open market place is characterized of decreased human thermal comfort conditions during summer time. The employment of computational fluid dynamics has contributed in the understanding of what interventions should be made at the open space in order to succeed the defined thermal related targets. Table of the proposed rehabilitation explains what the interventions would contribute in the improvement of the local environment.The authors greatly acknowledge the support of the Mayor of Eordaia Mrs Paraskevi Vrizidou during all simulation stages. ANSYS-CFD simulations were carried out in the framework of student instruction and demonstration of the Department of Environmental Engineering, Democritus University of Thrace in Greece

Lung Megakaryocytes are Immune Modulatory Cells that Present Antigen to CD4+ T cells.

Although platelets are the cellular mediators of thrombosis, they are also immune cells. Platelets interact both directly and indirectly with immune cells, impacting their activation and differentiation, as well as all phases of the immune response. Megakaryocytes (Mks) are the cell source of circulating platelets, and until recently Mks were typically only considered bone marrow–resident (BM-resident) cells. However, platelet-producing Mks also reside in the lung, and lung Mks express greater levels of immune molecules compared with BM Mks. We therefore sought to define the immune functions of lung Mks. Using single-cell RNA sequencing of BM and lung myeloid-enriched cells, we found that lung Mks, which we term MkL, had gene expression patterns that are similar to antigen-presenting cells. This was confirmed using imaging and conventional flow cytometry. The immune phenotype of Mks was plastic and driven by the tissue immune environment, as evidenced by BM Mks having an MkL-like phenotype under the influence of pathogen receptor challenge and lung-associated immune molecules, such as IL-33. Our in vitro and in vivo assays demonstrated that MkL internalized and processed both antigenic proteins and bacterial pathogens. Furthermore, MkL induced CD4+ T cell activation in an MHC II–dependent manner both in vitro and in vivo. These data indicated that MkL had key immune regulatory roles dictated in part by the tissue environment.pre-print236 K

Function of the Diiron Cluster of Escherichia coli Class Ia Ribonucleotide Reductase in Proton-Coupled Electron Transfer

The class Ia ribonucleotide reductase (RNR) from Escherichia coli employs a free-radical mechanism, which involves bidirectional translocation of a radical equivalent or “hole” over a distance of ~35 Å from the stable diferric/tyrosyl-radical (Y[subscript 122]•) cofactor in the β subunit to cysteine 439 (C[subscript 439]) in the active site of the α subunit. This long-range, intersubunit electron transfer occurs by a multistep “hopping” mechanism via formation of transient amino acid radicals along a specific pathway and is thought to be conformationally gated and coupled to local proton transfers. Whereas constituent amino acids of the hopping pathway have been identified, details of the proton-transfer steps and conformational gating within the β sununit have remained obscure; specific proton couples have been proposed, but no direct evidence has been provided. In the key first step, the reduction of Y[subscript 122]• by the first residue in the hopping pathway, a water ligand to Fe[subscript 1] of the diferric cluster was suggested to donate a proton to yield the neutral Y[subscript 122]. Here we show that forward radical translocation is associated with perturbation of the Mössbauer spectrum of the diferric cluster, especially the quadrupole doublet associated with Fe[subscript 1]. Density functional theory (DFT) calculations verify the consistency of the experimentally observed perturbation with that expected for deprotonation of the Fe[subscript 1]-coordinated water ligand. The results thus provide the first evidence that the diiron cluster of this prototypical class Ia RNR functions not only in its well-known role as generator of the enzyme’s essential Y[subscript 122]•, but also directly in catalysis.National Institutes of Health (U.S.) (GM-29595