Multidimensional Optimized Optical Modulation Formats

This chapter overviews the relatively large body of work (experimental and theoretical) on modulation formats for optical coherent links. It first gives basic definitions and performance metrics for modulation formats that are common in the literature. Then, the chapter discusses optimization of modulation formats in coded systems. It distinguishes between three cases, depending on the type of decoder employed, which pose quite different requirements on the choice of modulation format. The three cases are soft-decision decoding, hard-decision decoding, and iterative decoding, which loosely correspond to weak, medium, and strong coding, respectively. The chapter also discusses the realizations of the transmitter and transmission link properties and the receiver algorithms, including DSP and decoding. It further explains how to simply determine the transmitted symbol from the received 4D vector, without resorting to a full search of the Euclidean distances to all points in the whole constellation

Spectral efficiency improvement of low peak-to-average power ratio complete complementary code division multiple access systems

An investigation into the peak-to-average power ratio (PAPR) performance of cyclic rotation complete complementary code division multiple access (CR-CC-CDMA) has been conducted. Additionally, a novel orthogonal signalling technique, referred to as complementary rotation keying (CRK), has been developed for improving the spectral efficiency (SE) of CC-CDMA whilst maintaining a low PAPR. The CRK system is based on the concept of CR of CC codes in order to allow interoperability with CR-CC-CDMA systems. To this end, both systems employ a similar transmitter and receiver structure. The CR-CC-CDMA technique suffers from increased PAPR as SE per user is increased. The CRK system offers an improvement in SE, while maintaining the PAPR of a CC-CDMA system. The bit error rates of both systems were unaffected in a joint system, indicating complete interoperability. This allows dynamic adjustment of the PAPR and SE of any user in the system, with users being able to switch between both systems without causing multi user interference.Dissertation (MEng)--University of Pretoria, 2018.Electrical, Electronic and Computer EngineeringMEn

Acceptor-Substituted Cyclopentadienyl Compounds

Efficient methodologies for the synthesis of acceptor-substituted perfunctionalized cyclopentadienyl (Cp) compounds were investigated. A facile multigram, one-pot synthesis of [FeC10(HgO2CC3H7)10] from ferrocene and Hg(O2CC3H7)2 is reported. In the corresponding compound, the Hg-C bonds are inert towards oxygen, moisture and even strong Brønsted acids like trifluoroacetic acid and [C5F5NH][SbF6]. Instead, protonation of the carboxylic groups is observed yielding [FeC10(HgO2CCF3)10] and [FeC10Hg10(C5F5N)n][SbF6]10. In the compound [FeC10Hg10(C5F5N)n][SbF6]10, the labile C5F5N ligands are readily displaced by MeCN or tetrahydrothiophene (THT) to afford rare examples of organometallic decacations [FeC10(HgL)10][SbF6]10 (L = MeCN, THT). Electrochemical investigations on the (soluble) permercurated compounds reveal increasing redox potentials of the corresponding Fe(II)/Fe(III) redox couples with increasing Lewis acidity of the Hg-sites. The isolation of the oxidized forms was realized by reaction with [NO]+ or [NO2]+ salts or MoF6. Furthermore, the first crystallographic characterization of permetalated aromatic compounds [FeC10(HgX)10] (X = Cl, O2CCF3, O2CCCl3), [FeC10(HgTHT)10][SbF6]10 and [FeC10(HgMeCN)10][SbF6]10[MoF6] is presented. Complete halodemercuration is observed in the reaction of [FeC10(HgO2CC3H7)10] with K[Br3] followed by halogenation with FeBr3 and elemental Br2. An oxidation potential of E1/2 = 1.1V renders the corresponding ferrocenium cation as potent oxidizing agent. The isolation is realized by reaction of [FeC10Br10] with AsF5. Further functionalization of [FeC10Br10] is achieved by metalation with elemental Mg or by lithium-halogen-exchange with tBuLi. Quenching experiments with dimethylsilylchloride (DMSCl) yielded polysilylated compounds. Full functionalization was achieved after multiple metalation-silylation sequences. The resulting product [FeC10DMS10] displays the first example of a persilylated metallocene. A series of polysilylated derivatives [FeC10DMSnH10-n] (n = 7, 8, 9, 10) is analyzed by CV, single-crystal XRD, NMR and UV/VIS spectroscopy to evaluate the effect of silylation on the electronic properties of metallocenes. The obtained data are supported by quantum-chemical calculations. In the context of perhalogenated Cp compounds, the reaction of C5X6 (X = Cl, Br) with AsF5 and SbF5 is investigated. Here, the formation of unprecedented [2+2]-cycloaddition products of two Cp cations [C5X5]+ is observed. The obtained dications [C10X10]2+ are analyzed by XRD and NMR spectroscopy. DFT calculations reveal that the dimerzation to [2+2]- instead of [2+4]-products is thermodynamically preferred due to the formation of two allylic p-electron systems. Furthermore, in cooperation with the group of Prof. Dr. Schulz the electrochemical properties of [C5(C6F5)5]+ are presented

Header Compression and Signal Processing for Wideband Communication Systems.

This thesis is dedicated to the investigation, development and practical verification of header compression and signal processing techniques over TErrestrial Trunked RAdio (TETRA), TETRA Enhanced Data Services (TEDS) and Power Line Communication (PLC). TETRA release I is a narrowband private mobile radio technology used by safety and security organizations, while TEDS is a widebandsystem. With the introduction of IP support, TEDS enables multimedia based applications and services to communicate across communication systems. However the IP extension for TEDS comes at a cost of significant header contributions with the payload. With small application payloads and fast rate application traffic profiles, the header contribution in the total size of the packet is considerably more than the actual application payload. This overhead constitutes the considerable slot capacity at the physical layer of TEDS and PLC. Advanced header compression techniques such as Robust Header Compression (RoHC) compress the huge header sizes and offer significant compression gain without compromising quality of service (QoS). Systems can utilize this bandwidth to transmit more information payload than control information. In this study, the objective is to investigate the integration of RoHC in TEDS and design a novel IPv6 enabled protocol stack for PLC with integrated RoHC. The purpose of the study is also to investigate the throughput optimization technique such as RoHC over TEDS and PLC by simulating different traffic profile classes and to illustrate the benefit of using RoHC over TEDS and PLC. The thesis also aims to design and simulate the TEDS physical layer for the purpose of investigating the performance of higher order modulation schemes. Current TEDS, standards are based on the transmission frequencies above 400MHz range, however with delays in the standardization of broadband TETRA, it is important to explore all possible avenues to extend the capacity of the system. The research concludes the finding of the application of RoHC for TEDS and PLC, against different traffic classes and propagation channels. The benefit of using RoHC in terms of saving bandwidth, slot capacity and other QoS parameters is presented along with integration aspects into TEDS and PLC communication stacks. The study also presents the TEDS physical layer simulation results for modulation schemes and transmission frequency other than specified in the standard. The research results presented in this thesis have been published in international symposiums and professional journals. The application of the benefits of using RoHC for TEDS has been proposed to the ETSI TETRA for contribution to the TETRA standard under STF 378. Simulation results for the investigation of characteristics of ?/4 DQPSK performance below 200 MHz have also been also presented to ETSI TETRA as a contribution to the existing TEDS standard. The Results presented for the design of IPv6 enabled stacked with integrated RoHC have been submitted as deliverable under the FP-7 project DLC+VIT4IP. All the results, simulations and investigations presented in the thesis have been carried out through the platform provided by HW Communication Ltd

The 1999 Center for Simulation of Dynamic Response in Materials Annual Technical Report

Introduction: This annual report describes research accomplishments for FY 99 of the Center for Simulation of Dynamic Response of Materials. The Center is constructing a virtual shock physics facility in which the full three dimensional response of a variety of target materials can be computed for a wide range of compressive, ten- sional, and shear loadings, including those produced by detonation of energetic materials. The goals are to facilitate computation of a variety of experiments in which strong shock and detonation waves are made to impinge on targets consisting of various combinations of materials, compute the subsequent dy- namic response of the target materials, and validate these computations against experimental data

Applications of density functional theory (DFT) to investigate the structural, spectroscopic and magnetic properties of lanthanide(III) complexes

[Abstract] Density functional theory (DFT) has become a general tool to investigate the structure and properties of complicated inorganic molecules, such as lanthanide(III) coordination compounds, due to the high accuracy that can be achieved at relatively low computational cost. Herein, we present an overview of different successful applications of DFT to investigate the structure, dynamics, vibrational spectra, NMR chemical shifts, hyperfine interactions, excited states, and magnetic properties of lanthanide(III) complexes. We devote particular attention to our own work on the conformational analysis of LnIII-polyaminocarboxylate complexes. Besides, a short discussion on the different approaches used to investigate lanthanide(III) complexes, i. e. all-electron relativistic calculations and the use of relativistic effective core potentials (RECPs), is also presented. The issue of whether the 4f electrons of the lanthanides are involved in chemical bonding or not is also shortly discussed.Ministerio de Educación y Ciencia; CTQ2009-10721Xunta de Galicia; IN845B-2010/06

Space programs summary no. 37-46, volume IV FOR the period June 1 to July 31, 1967. Supporting research and advanced development

Spacecraft guidance and control, propulsion, telecommunications, and systems analysis, and space science researc

Synthetic and computational investigations into reaction pathways towards complex heterocyclic ring systems

Tetrazocines are eight-membered rings possessing four nitrogen atoms. The development of new synthetic routes to novel heterocyclic systems has remained a critical branch of synthetic organic chemistry due to potential applications in biomimetics and pharmaceuticals, such as dyes and explosives. 1,2,3,5-tetrazocines were originally proposed as an intermediate in the formation of 1,3a,6,6atetrahydroimidazo[4,5-c]pyrazole (a promising anti-fungal agent) from the irradiation of 2,3a,4,6a-tetraphenyl-3,3a,4,5,6,6a hexahydropyrrolo-[2,3-d]-1,2,3-triazole. One of our main aims was to synthesise novel 1,2,3,5-tetrazocines that possessed three phenyl and one methyl group(s) attached to the eight-membered ring, as previously synthesised 1,2,3,5-tetrazocines are of the tetra-phenyl variety. Adopting the established synthetic route in the pursuit of novel 1,2,3,5-tetrazocines proved difficult however, as the asymmetric nature of the 1,2,3,5-tetrazocine precursors (dihydrazones) resulted in altered reactivity as compared with their symmetric equivalents, this finding was rationalised using distributed multipole analysis. Ab initio calculations (B3LYP/6-31G(d)) indicate that for an underivatised 1,2,3,5- tetrazocine, the planar (aromatic) structure is the most stable, though this is not observed experimentally, presumably due to steric repulsions between the large aromatic substituents often used to stabilise these molecules. Excluding the planar geometry, we found that there is a significant thermodynamic stabilisation of 1,2,3,5- tetrazocine over the 1,3a,6,6a-tetrahydroimidazo[4,5-c]pyrazole, providing a novel route to heterocyclic systems