Fixed-time observer-based distributed secondary voltage and frequency control of islanded AC microgrids

This paper deals with the problem of voltage and frequency control of distributed generators (DGs) in AC islanded microgrids. The main motivation of this work is to obviate the shortcomings of conventional centralized and distributed control of micro-grids by providing a better alternative control strategy with better control performance than state-of-the art approaches. A distributed secondary control protocol based on a novel fixed-time observer-based feedback control method is designed for fixed-time frequency and voltage reference tracking and disturbance rejection. Compared to the existing secondary microgrid controllers, the proposed control strategy ensures frequency and voltage reference tracking and disturbance rejection before the desired fixed-time despite the microgrid initial conditions, parameters uncertainties and the unknown disturbances. Also, the controllers design and tuning is simple, straightfor-ward and model-free.i.e, the knowledge of the microgrid parameters, topology, loads or transmission lines impedance are not needed in the design procedure. The use of distributed control approach enhances the reliability of the system by making the control system geographically distributed along with the power sources, by using the neighboring DGs informations instead of the DG’s local informations only and by cooperatively rejecting external disturbances and maintaining the frequency and the voltage at their reference values at any point of the microgrid. The efficiency of the proposed approach is verified by comparing its performance in reference tracking and its robustness to load power variations to some of the works in literature that addressed distributed secondary voltage and frequency control

Transition-metal norharmane compounds as possible cytotoxic agents: new insights based on a coordination chemistry perspective

New first-row transition-metal compounds with the ligand norharmane (9H-Pyrido[3,4-b]indole; Hnor) are reported. The compounds have the general formula [M(LL)(Hnor)(NO3)2](MeOH)0–1 (M = Co, Ni, Cu, Zn; LL = 2,2′-bipyridyl (bpy), 1,10-phenanthroline (phen)) and have been characterized by physical and analytical methods. X-ray structural analysis revealed that the compound of formula [Cu(phen)(Hnor)(NO3)2], (1) has a distorted 6-coordinated octahedrally-based geometry, with a planar-based [CuN3O] core, where Cu-L varies between 1.99 and 2.04 Å and two weak axial Cusingle bondO contacts (2.209 and 2.644 Å) from two different nitrates. Based on spectroscopic similarities, the other compounds appear to have the same or very similar coordination geometries. The compounds showed clear cell growth inhibitory effects in two different cancer cell lines in vitro, with the copper and zinc complexes being the most toxic and in fact almost comparable to cisplatin. Flow-cytometry analysis confirmed induction of apoptosis in cancer cells treated with the compounds. Interestingly, co-incubation of the cells with metal complexes and CuCl2 induced an increase in the cytotoxic effects, most likely due to the conversion of the metal compounds in the corresponding, and most active, copper analogues

Azide, water and adipate as bridging ligands for Cu(II) : synthesis, structure and magnetism of (μ4-adipato-κ-O)(μ-aqua)(μ-azido-κN1,N1)copper(II) monohydrate

The Distinguished Scientist Fellowship Program (DSFP) at King Saud University is gratefully acknowledged. The authors are grateful to the Algerian MESRS (Ministère de l’Enseignement Supérieur et de la Recherche Scientifique), the Université Ferhat Abbas Sétif 1, the KSU DSFP program and the Spanish MINECO (CTQ2014-52758-P and MAT2014-56143-R) and the Generalitat Valenciana (PrometeoII/2014/076) for financial support.The synthesis, characterization, single crystal structure and magnetic properties of the compound [(CuN3(OH2))2(adp)]n (1) are presented, in which adp stands for the adipate(2-) anion. This compound consists of layers containing chains of six-coordinated Cu(II) ions; the chains are connected by μ4adipate anions. The magnetically interesting part of the compound is the Cu(II) chain, built from 3 bridging ligands, i.e. a water ligand, an azide anionic ligand bridging by using a terminal N atom to connect 2 Cu(II) ions, and one symmetrically bridging carboxylato group of adipate; the other end of the tetradentate adipate anions symmetrically connect the chains, forming the layers. From the magnetic point of view the compound is considered as a Cu(II) chain with a quite unusual, symmetrical water bridge, the μ-syn-syn carboxylate and the μ-N3 bridge. The bridging water also hydrogen bonds to a terminal N of a nearby azido ligand. Magnetic susceptibility measurements show that 1 presents moderate ferromagnetic intrachain interactions (Jchain = +38.4 cm-1) with a metamagnetic behaviour for the inter-chain interaction with a critical field of 0.7 T.PostprintPeer reviewe

1-[1-(3-Methyl­phen­yl)-5-phenyl-4-phenyl­sulfonyl-1H-pyrazol-3-yl]ethanone

Both the acetyl and phenyl substituents of the central pyrazole ring in the title compound, C24H20N2O3S, are twisted with respect to the pyrazole ring, with the twist involving the phenyl ring being greater [67.4 (1) and 29.6 (2)°]. The tolyl substituent is disordered over two positions in a 1:1 ratio; the mean planes of the aromatic ring are aligned at 67.7 (3) and 69.4 (3)° with respect to the pyrazole ring

catena-Poly[[bis­(N,N′-dimethyl­formamide)cadmium(II)]-μ2-oxalato]

The title compound, [Cd(C2O4)(C3H7NO)2]n, is isostructural with its MnII analogue. The structure comprises zigzag polymeric chains with the oxalate groups situated on inversion centres and the CdII atoms located on twofold rotation axes. The coordination geometry around CdII is distorted octa­hedral and the intra­chain Cd⋯Cd distance is 5.842 (1) Å. C—H⋯O hydrogen bonds exist between the parallel polymeric chains

N′-(Di-2-pyridylmethyl­ene)benzo­hydrazide

In the title Schiff base, C18H14N4O, the amido –NH– unit is connected to one of the two pyridyl N atoms at an N(—H)⋯N distance of 2.624 (2) Å. The mol­ecular packing features an inter­molecular C—H⋯N R 2 2(6) hydrogen-bonding ring motif

2-Chloro­pyrimidin-4-amine

In the title pyrimidine derivative, C4H4ClN3, the 2-chloro and 4-amino substituents almost lie in the mean plane of the pyrimidine ring, with deviations of 0.003 (1) Å for the Cl atom, and 0.020 (1) Å for the N atom. In the crystal, molecules are linked via pairs of N—H⋯N hydrogen bonds, forming inversion dimers. These dimers are further linked via N—H⋯N hydrogen bonds, forming an undulating two-dimensional network lying parallel to (100)

Structural chemistry and optical application

The demand for materials with optical activities against LASER radiation has been extensively increased over the last decade with the development of sophisticated high energetic LASER sources. The goal is to obtain organic or metal-organic molecules capable of increasing their absorptions against LASER irradiance while still maintaining a degree of transmittance. For instance, Zn-meso-tetrakis [bromothiophene] porphyrin is presented here as an efficient optical power limiter against Nd:YAG beam. Moreover, Schiff’s bases based on bromothiophenes show a degree of NLO performance against LASER. Single crystal X-ray crystallography has represented an active area of research leading to better understanding of many chemical and structural phenomena, thus the geometrical and electronic analogy for the fourth and the fifth bromine atoms position at the thiophene ring had been addressed. This thesis describes porphyrins, metalloporphyrins and conjugated thiophenes as optical limiters and non-linear optical materials with insight on the chemical and physico-chemical theories describing these actions. The organic molecules prepared in this work are meso-tetrakis 4-and 5-Bromo thiophene porphyrins, Bis thiophenyl 2-methylene hydrazine, Bis 4-bromothiophenyl 2-methylene hydrazine and Bis 5-bromothiophenyl 2-methylene hydrazine. The metal-organic molecules prepared in this work are Ag (II), Zn (II) meso-tetrakis 4- and 5-Bromo thiophene porphyrins as well as Zn (II) trans-bis nicotinato chloride. The syntheses, characterizations and optical properties as well as x-ray crystal structures of 2 metal-organic and 3 organic structures are presented and discussed

Real time scheduling in distributed video servers

This dissertation addresses the scheduling problem of video requests in a distributed video file server system. The objective of our scheduling technique is to increase the load balancing performance among the distributed video file servers and eventually, to minimize the delay for the video request objects to be serviced. In order to achieve this objective, we propose a load balancing algorithm called "NOVA " to perform dynamic scheduling of the video requests and to balance the load among the distributed video file servers so as to achieve an near optimal solution. We provide an experimental study in which our algorithm, compared to landmark algorithms, show improved performance in terms of load balancing, scalability and less delay for the video requests to be serviced.Master of Science (Communication and Network Systems

Controlling function by structure-intermolecular interactions and crystal engineering with N-donor ligands

In the solid state regime, crystal engineering based on non-covalent synthesis requires an intuition about the intermolecular forces that can dictate the molecular architecture. Hydrogen bonds have become an instrumental tool in the self assembly and supramolecular chemistry. A variety of Schiff’s bases ligands based on azomethine functional units have been synthesized by condensation of the corresponding aldehydes with hydrazine monohydrate and their structures have been revealed by X-ray diffraction. The Br\ub7\ub7\ub7Br intermolecular interaction in Cambridge Structural Database was studied and a relation between OPL measurements and the positions of bromine atoms in two Schiff’s bases has been drawn. A 2D square grid coordination polymer with a dimension of 16 716\uc5 based on Fe(II) metal centers and bis-pyridinyl methylene hydrazine organic spacer had been assembled and the structure was characterized by X-ray single-crystal diffraction. The square grid with an accessible voids volume of ca. 20% is also hosting [Fe(phen)3]2+ complex as well as free ligand and water solvates which represent a unique example of a coordination polymer host capable of intercalating neutral and cationic guests. The guests assembled inside these grids has independently synthesized and characterized by X-ray single crystal diffraction where σ-π and π-π stacking are the only intermolecular interactions controlling their intercalation behaviour. A different stoichiometry resulted in an 1D coordination chain of Fe(II) centers where the sheets of arrays are supported by hydrogen bonding building up an infinite 2D square grid assembly. Different hydrogen bonding motifs varied with different counter ions in the case of the solely ligands have been emphasized. The crystal packing of 4-bromothiophene porphyrin-Zn(II) was shown to depend on S\ub7\ub7\ub7S non-covalent interactions and OPL properties of the free bases and Ag(II) porphyrins are discussed. A homochiral double helical packing caused by S\ub7\ub7\ub7S interactions in [Co(SCN)4]2- with [Ru(phen)3]2+ is manifested