Generation of pure electrical quadrature amplitude modulation with photonic vector modulator

A photonic vector modulator architecture for generating pure quadrature amplitude modulation (QAM) signals is presented. An electrical quadrature-modulated signal at microwave-millimeter-wave frequencies is generated from its corresponding baseband in-phase (I) and quadrature (Q) components. In the proposed scheme, no electrical devices apart from the electrical tone oscillator are needed in the generation process. In addition, the purity of the generated signal is increased, and the hardware requirements are reduced when compared with previously proposed architectures so a highly compact low-cost architecture can be implemented. A pure 1.25 Gbit/s 4-QAM signal has been experimentally generated at a 42 GHz carrier frequency.     

Ten gigabits per second 16-level quadrature amplitude modulated millimeter-wave carrier generation using dual-drive Mach-Zehnder modulators incorporated photonic-vector modulator

A novel photonic-vector modulator architecture for the generation of 16 quadrature amplitude modulation (16 QAM) millimeter-wave carriers using dual-drive Mach-Zehnder modulators is proposed. Experimental generation of 5 Gbits/s 4 amplitude shift-keying (4 ASK) and 10 Gbits/s 16 QAM modulated 42 GHz carriers is reported. The multilevel modulated millimeter-wave signals are demodulated using an electrical receiver and its error-vector magnitude (EVM) estimated from the measurements, obtaining EVMs of -21.04 and -18.33 dB for 4 ASK and 16 QAM modulation formats, respectively.     

Sull'equilibrio isotermo dei corpi elastici con un vincolo di appoggio unilaterale liscio nel caso di deformazioni finite

Summary We study the analytical problem connected with the isothermal equilibrium of an elastic body with an unilateral supporting constraint on an indeformable frictionless surface in the case of? finite? deformations. As a first approach to investigate this boundary-value problem, we think of the external active forces as linearly dipending upon a parameter: this leads to consider a finite or infinite sequence of linear differential systems(? auxiliary? systems). In§ 2 we show how one can determine the (unilateral) boundary-value problem to be associated to each auxiliary system.§ 3 is dedicated to study the uniqueness of the solution of the auxiliary systems by means of the analysis of the conditions for the integrability of the successive auxiliary systems. The investigation of uniqueness leads to a classification into several types of the supporting surfaces and requires, for each of these types, a systematic study of the integrability conditions. In this manner we can verify that the boundary-value problem for the auxiliary systems has been? correctly set?. ln§ 4 we deal with the existence problem for the generical auxiliary system; we show the possibility of a weak, integral-type formulation—expressed only in terms of the stress-components—for the boundary-value problem associated to the generical auxiliary system and we come to an existence theorem expressible only in terms of stress, though the boundary conditions concern also the displacement.

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Entrato in Redazione il 17-XI-1973.

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Lavoro eseguito nell'ambito del Gruppo Nazionale per la Fisica Matematica del C.N.R.     

Variability in phenolic composition of Hypericum androsaemum

The methanolic extracts of fifteen Hypericum androsaemum samples, growing spontaneously or cultivated in Portugal, were analysed by HPLC/DAD, allowing the identification of 9 phenolic compounds and the detection of 6 phloroglucinols. Total amounts of phenolics found ranged from 11 to 39 g/kg, and the influence of some factors which may be responsible for this variation is discussed. The individual compounds were also quantified. Four different phenolic profiles were found concerning both qualitative and quantitative composition, indicating the possible existence of chemical polymorphism.     

A generalized Ginzburg-Landau approach to second harmonic generation

We develop a generalized Ginzburg-Landau theory for second harmonic generation (SHG) in magnets by expanding the free energy in terms of the order parameter in the magnetic phase and the susceptibility tensor in the corresponding high-temperature phase. The non-zero components of the SHG susceptibility in the ordered phase are derived from the symmetries of the susceptibility tensor in the high-temperature phase and the symmetry of the order parameter. In this derivation, the dependence of the SHG susceptibility on the order parameter follows naturally, and therefore its nonreciprocal optical properties. We examine this phenomenology for the magnetoelectric compound Cr₂O₃ as well as for the ferroelectromagnet YMnO₃. Received 27 August 1999     

Nickel‐Catalyzed Cross‐Coupling of Organolithium Reagents with (Hetero)Aryl Electrophiles

Nickel‐catalyzed selective cross‐coupling of aromatic electrophiles (bromides, chlorides, fluorides and methyl ethers) with organolithium reagents is presented. The use of a commercially available nickel N‐heterocyclic carbene (NHC) complex allows the reaction with a variety of (hetero)aryllithium compounds, including those prepared via metal‐halogen exchange or direct metallation, whereas a commercially available electron‐rich nickel‐bisphosphine complex smoothly converts alkyllithium species into the corresponding coupled product. These reactions proceed rapidly (1 h) under mild conditions (room temperature) while avoiding the undesired formation of reduced or homocoupled products.     

Superintegrable models on Riemannian surfaces of revolution with integrals of any integer degree (I)

We present a family of superintegrable (SI) systems which live on a Riemannian surface of revolution and which exhibit one linear integral and two integrals of any integer degree larger or equal to 2 in the momenta. When this degree is 2, one recovers a metric due to Koenigs.The local structure of these systems is under control of a linear ordinary differential equation of order n which is homogeneous for even integrals and weakly inhomogeneous for odd integrals. The form of the integrals is explicitly given in the so-called “simple” case (see Definition 2). Some globally defined examples are worked out which live either in H² or in R².     

tBuLi‐Mediated One‐Pot Direct Highly Selective Cross‐Coupling of Two Distinct Aryl Bromides

A Pd‐catalyzed direct cross‐coupling of two distinct aryl bromides mediated by tBuLi is described. The use of [Pd‐PEPPSI‐IPr] or [Pd‐PEPPSI‐IPent] as catalyst allows for the efficient one‐pot synthesis of unsymmetrical biaryls at room temperature. The key for this selective cross‐coupling is the use of an ortho‐substituted bromide that undergoes lithium–halogen exchange preferentially.     

Locking of Turing patterns in the chlorine dioxide-iodine-malonic acid reaction with one-dimensional spatial periodic forcing

We use the photosensitive chlorine dioxide-iodine-malonic acid reaction-diffusion system to study wavenumber locking of Turing patterns with spatial periodic forcing. Wavenumber-locked stripe patterns are the typical resonant structures that labyrinthine patterns exhibit in response to one-dimensional forcing by illumination when images of stripes are projected on a working medium. Our experimental results reveal that segmented oblique, hexagonal and rectangular patterns can also be obtained. However, these two-dimensional resonant structures only develop in a relatively narrow range of forcing parameters, where the unforced stripe pattern is in close proximity to the domain of hexagonal patterns. Numerical simulations based on a model that incorporates the forcing by illumination using an additive term reproduce well the experimental observations. These findings confirm that additive one-dimensional forcing can generate a two-dimensional resonant response. However, such a response is considerably less robust than the effect of multiplicative forcing.