Two-dimensional E-field mapping with subpicosecond temporal resolution

A new contactless reflection-mode electro-optic sampling technique is described which is capable of characterising the electrical response of microstructures in two dimensions with micrometre spatial resolution, a temporal response of a fraction of a picosecond and millivolt sensitivity. A GaAs-based sampling technique which would have minimum interference with the test circuit is also proposed.     

Analysis and Design of RF CMOS Attenuators

Attenuators are analyzed for their minimum Insertion Loss (IL), maximum attenuation and source-load matching performance. These results are used to make trade-offs in the design of a CMOS attenuator with wide dynamic range, designed and fabricated in a 0.13 mum CMOS process. The design employs two non-identical cascaded T-stages that are activated consecutively to improve linearity. The design operates in the frequency band of DC-2.5 GHz with 0.9-3.5 dB insertion loss and 42 dB maximum attenuation in the entire frequency range. Worst case S11 is - 8.2 dB across the frequency band. The design achieves an IIP3 of + 20 dBm at mid-attenuation.     

Metric semantics for concurrency

An overview is given of work we have done in recent years on the semantics of concurrency, concentrating on semantic models built on metric structures. Three contrasting themes are discussed, viz. (i) uniform or schematic versus nonuniform or interpreted languages; (ii) operational versus denotational semantics, and (iii) linear time versus branching time models. The operational models are based on Plotkin's transition systems. Language constructs which receive particular attention are recursion and merge, synchronization and global nondeterminacy, process creation, and communication with value passing. Various semantic equivalence results are established. Both in the definitions and in the derivation of these equivalences, essential use is made of Banach's theorem for contracting functions.Dedicated to Peter Naur on the occasion of his 60th birthday     

Molecular mechanics and molecular shape. V. on the computation of the bare surface area of molecules

This article examines the numerical estimation of molecular surface areas within the model of overlapping atomic spheres. One has the choice of either basing the estimate on all elements that contribute to the surface, or of ignoring systematically some elements in the interatomic clefts. It is argued that the second choice, even though more approximate, implicitly improves on the model and is to be preferred. Since surface areas are not measurable, the demonstration is unavoidably roundabout, relying mostly on correlation analysis. Among the regressors occur two compounded parameters. One, ratio of the surface area of the equivalent sphere to the surface area, is interpreted as a measure of molecular globularity. It reflects the molecular axis-ratio and surface convolution. The other, ratio of the surface area to the volume, is interpreted as a measure of the global congestion of a chemical residue. Together with a measure of the local congestion at the point of attachment, it affects the steric hindrance that a residue offers. The relation between the surface area and the number of valence electrons is also discussed.     

On-line γ-ray investigation of the14N+27Al reaction at 30 MeV/u

The cross-sections of target-like residues following the¹⁴N+²⁷Al reaction at 30 MeV/u have been measured from in-beam and radioactiveγ-ray spectra. The recoil velocities of some fragments have been estimated from theγ-ray Doppler broadening.     

Decay of the 21/2− isomer in211Bi and structure of thevg 9 2/2 πh 9/2 levels

Gamma rays and conversion electrons have been measured in²¹¹Bi populated by the²⁰⁹Bi(t,p) reaction, and the near yrast levels were observed up to 21/2^?. The 21/2^? state is isomeric withT _1/2=70(5) ns. No alpha decaying isomer was found in²¹¹Bi. ObservedM1 transitions reveal mixing of the²¹⁰Pb parent states in the levels of²¹¹Bi. The levels and transitions are well reproduced by the shell model with experimental matrix elements and pure configurations.