A VLSI CMOS delay oriented waveform converter for polyphasefrequency synthesizer

In this paper, we present a waveform converter implemented on a 0.25-μm CMOS technology using a dedicated design methodology (Delay Oriented Design). The circuit converts a square wave signal in both in-phase and quadrature-phase sinusoidal differential outputs. It also multiplies the frequency by seven. The output frequency range of this converter extends from 1.05 GHz up to 2.17 GHz. This converter is dedicated for the design of a third-generation mobile phone synthesizer using a double-loop architecture. For an output frequency of 2 GHz, the measured phase noise at 10-kHz offset from the carrier is -97 dBc/Hz. The circuit consumes 50 mW from a 2.5-V supply     

The comparison of thermal stability of some hydrofluoroethers and hydrofluoropolyethers

The thermal stability of representative hydrofluoropolyether (HFPE) and hydrofluoroether (HFE) compounds has been evaluated. The observed stability order appears to be correlated with the nature of the hydrogenated chain ends; in particular, molecules having fully hydrogenated chain ends (OCH₃ and OC₂H₅) show a significantly lower stability compared with the OCF₂H terminated compounds. The main degradation products suggest, however, that the same primary reaction is responsible for the decomposition of all the compounds examined; this reaction involves the fragmentation of the R_fOC_xH_yF_z bond with fluorine transfer between the two carbon atoms close to the oxygen, leading to the formation of a hydrofluorocarbon C_xH_yF_(z+1) and an acyl fluoride or a ketone.     

Synthesis of low molecular weight perfluoro oxymethylene vinyl ethers

Perfluoro oxymethylene vinyl ethers have been formed by a multi-step synthesis. The key intermediates are low molecular weight perfluoropolyether (PFPE) fluoroformates CF₃O(CF₂O)_nCOF (I) n=1-6 obtained from the photo-oxidation of perfluoro propene (HFP) in perfluorohexane. Under certain conditions the light-mediated fluorination of PFPE fluoroformates (I) gives PFPE hypofluorites CF₃O(CF₂O)_nCF₂OF (II), which can be added to sym dichlorodifluoroethene to form the dichloro adduct CF₃O(CF₂O)_nCF₂OCFClCF₂Cl (III) which, after dechlorination, gives the desired vinyl ethers CF₃O(CF₂O)_nCF₂OCFCF₂ (IV). Every reaction step has to be properly controlled as far as the reaction variables are concerned. A mechanistic scheme is presented that is consistent with the observed experimental data.     

HiperLAN 5.4-GHz low-power CMOS synchronous oscillator

A 5.4-GHz 0.25-μm very-large-scale-integration CMOS synchronous oscillator (SO) is proposed in this paper, which is designed to act as a local oscillator for HiperLAN systems. The advantage of using such an oscillator in a double-loop frequency synthesizer is demonstrated. The design strategy leading to an optimized SO with regards to its synchronization range is described. A test chip is presented, which provides a 150-MHz synchronization range and a -97-dBc/Hz phase noise at 10-kHz offset from the 5-GHz carrier, while consuming only 5 mA from a 2.5-V supply     

Self-amplified spontaneous emission free-electron laser with an energy-chirped electron beam and undulator tapering

We report the first experimental implementation of a method based on simultaneous use of an energy chirp in the electron beam and a tapered undulator, for the generation of ultrashort pulses in a self-amplified spontaneous emission mode free-electron laser (SASE FEL). The experiment, performed at the SPARC FEL test facility, demonstrates the possibility of compensating the nominally detrimental effect of the chirp by a proper taper of the undulator gaps. An increase of more than 1 order of magnitude in the pulse energy is observed in comparison to the untapered case, accompanied by FEL spectra where the typical SASE spiking is suppressed.     

Full characterization of colloidal solutions of long-alkyl-chain-amine-stabilized ZnO nanoparticles by NMR spectroscopy: surface state, equilibria, and affinity

Full NMR characterization of ZnO nanoparticles (NPs) stabilized by various amines (hexadecylamine, dodecylamine, and octylamine) in C(7)D(8) demonstrated that the surface of this apparently simple system was very complex. Using different NMR spectroscopic techniques ((1)H, PGSE-NMR, diffusion-filtered (1)H NMR, NOESY, ROESY), we observed at least three different modes of interaction of the amines at the surface of the NPs, in thermodynamic equilibrium with the free amines, the relative populations of which varied with their concentration. The first mode corresponded to a strong interaction between a small amount of amine and the ZnO NPs (k(desorp)≈13 s(-1)). The second mode corresponded to a weak interaction between the amines and the surface of the ZnO NPs (k(off(2))≈50-60 s(-1)). The third, and weakest, mode of interaction corresponded to the formation of a second ligand shell by the amine around the NPs that was held together through van der Waals interactions (k(off(1))≈25×10(5) s(-1)). The second and third modes were in fast exchange on the NMR timescales with the free amines. The strongly interacting amines at the NPs surface (first mode) were in slow exchange with the other modes. A complex hydrogen-bonding network at the NPs surface was also observed, which did not only involve the coordinated amine but also THF and water molecules that remained from the synthesis.     

Design studies of the PWO Forward End-cap calorimeter for P̄ANDA

The P?ANDA detection system at FAIR, Germany, is designed to study antiproton-proton annihilations, in order to investigate, among others, the realm of charm-meson states and glueballs, which has still much to reveal. The yet unknown properties of this field are to be unraveled through studying QCD phenomena in the non-perturbative regime. The multipurpose P?ANDA detector will be capable of tracking, calorimetry, and particle identification, and is planned to run at high luminosities providing average reaction rates up to 2 · 10⁷ interactions/s. The envisaged physics program requires measurements of photons and charged particles with excellent energy, position, and time resolutions. The electromagnetic calorimeter (EMC) will serve as one of the basic components of the detector setup and comprises cooled lead-tungstate (PbWO₄) crystals. This paper presents the mechanical design of the Forward End-cap calorimeter and analyzes the response of the Forward End-cap calorimeter in conjunction with the full EMC and the complete P?ANDA detector. The simulation studies are focused on the performance of the planned EMC with respect to the energy and spatial resolution of the reconstructed photons. Results of the Monte Carlo simulations, excluding very low-energy photons, have been validated by data obtained from a prototype calorimeter and shown to fulfil the requirements imposed by the P?ANDA physics program.     

Full Characterization of Colloidal Solutions of Long‐Alkyl‐Chain‐Amine‐Stabilized ZnO Nanoparticles by NMR Spectroscopy: Surface State,Equilibria, and Affinity

Full NMR characterization of ZnO nanoparticles (NPs) stabilized by various amines (hexadecylamine, dodecylamine, and octylamine) in C₇D₈ demonstrated that the surface of this apparently simple system was very complex. Using different NMR spectroscopic techniques (¹H, PGSE‐NMR, diffusion‐filtered ¹H NMR, NOESY, ROESY), we observed at least three different modes of interaction of the amines at the surface of the NPs, in thermodynamic equilibrium with the free amines, the relative populations of which varied with their concentration. The first mode corresponded to a strong interaction between a small amount of amine and the ZnO NPs (k_desorp≈13 s^?1). The second mode corresponded to a weak interaction between the amines and the surface of the ZnO NPs (k_off(2)≈50–60 s^?1). The third, and weakest, mode of interaction corresponded to the formation of a second ligand shell by the amine around the NPs that was held together through van der Waals interactions (k_off(1)≈25×10⁵ s^?1). The second and third modes were in fast exchange on the NMR timescales with the free amines. The strongly interacting amines at the NPs surface (first mode) were in slow exchange with the other modes. A complex hydrogen‐bonding network at the NPs surface was also observed, which did not only involve the coordinated amine but also THF and water molecules that remained from the synthesis.     

Prominence of the Instability of a Stabilizing Agent in the Changes in Physical State of a Hybrid Nanomaterial

Shaping ability of hybrid nanomaterials is a key point for their further use in devices. It is therefore crucial to control it. To this end, it is necessary that the macroscopic properties of the material remain constant over time. Here, we evidence by multinuclear Magic-Angle Spinning Nuclear Magnetic Resonance spectroscopic study including ¹⁷O isotope exchange that for a ZnO-alkylamine hybrid material, the partial carbonation of amine into ammonium carbamate molecules is behind the conversion from highly viscous liquid to a powdery solid when exposed to air. This carbonation induces modification and reorganization of the organic shell around the nanocrystals and affects significantly the macroscopic properties of the material such as it physical state, its solubility and colloidal stability. This study, straightforwardly extendable, highlights that the nature of the functional chemical group allowing connecting the stabilizing agent (SA) to the surface of the nanoparticles is of tremendous importance especially if the SA is reactive with molecules present in the environment.