Additive manufacturing method of prototyping novel mm-wave and THz sources

To rapidly prototype novel mm-wave and THz sources there is a requirement to create intricate structures to produce and radiate electromagnetic fields. The motivation for this work is to create improved electron-beam-driven, vacuum electronic mm-wave and sub-THz sources by exploiting dispersion engineering. Although such structures can be manufactured by other techniques, additive manufacturing has proven to be quick, reliable and cost-effective. This research is allowing the prototyping of novel mm-wave and sub-THz coherent sources

Solvable Systems of Linear Differential Equations

The asymptotic iteration method (AIM) is an iterative technique used to find exact and approximate solutions to second-order linear differential equations. In this work, we employed AIM to solve systems of two first-order linear differential equations. The termination criteria of AIM will be re-examined and the whole theory is re-worked in order to fit this new application. As a result of our investigation, an interesting connection between the solution of linear systems and the solution of Riccati equations is established. Further, new classes of exactly solvable systems of linear differential equations with variable coefficients are obtained. The method discussed allow to construct many solvable classes through a simple procedure.Comment: 13 page

We are the Change that we Seek: Information Interactions During a Change of Viewpoint

There has been considerable hype about filter bubbles and echo chambers influencing the views of information consumers. The fear is that these technologies are undermining democracy by swaying opinion and creating an uninformed, polarised populace. The literature in this space is mostly techno-centric, addressing the impact of technology. In contrast, our work is the first research in the information interaction field to examine changing viewpoints from a human-centric perspective. It provides a new understanding of view change and how we might support informed, autonomous view change behaviour. We interviewed 18 participants about a self-identified change of view, and the information touchpoints they engaged with along the way. In this paper we present the information types and sources that informed changes of viewpoint, and the ways in which our participants interacted with that information. We describe our findings in the context of the techno-centric literature and suggest principles for designing digital information environments that support user autonomy and reflection in viewpoint formation

The Physical Principles of Quantum Mechanics. A critical review

The standard presentation of the principles of quantum mechanics is critically reviewed both from the experimental/operational point and with respect to the request of mathematical consistency and logical economy. A simpler and more physically motivated formulation is discussed. The existence of non commuting observables, which characterizes quantum mechanics with respect to classical mechanics, is related to operationally testable complementarity relations, rather than to uncertainty relations. The drawbacks of Dirac argument for canonical quantization are avoided by a more geometrical approach.Comment: Bibliography and section 2.1 slightly improve

Microwave coupler for W-band micro re-entrant square cavities

Klystrons are vacuum electronic devices widely used for microwave amplification up to the millimetre-wave region. The opportunity to push the operating frequency of conventional klystrons above 30–40 GHz is limited by the 20 fabrication difficulties of the cavities that have very small dimensions. A high order mode micro re-entrant square cavity was purposely devised to be compatible with the available micro fabrication processes and represents a viable solution for the design of millimetre-wave klystrons. In this study, a coupler to correctly excite the higher order mode of the square re-entrant cavities for W-band operation is proposed. The design of the proposed novel coupler structure has been validated by realisation and measurement of a scaled X-band prototype. The post-realisation tuning methods 25 adopted to improve the matching of the high order mode are also presented

Design and experiments of a five-fold helically corrugated waveguide for microwave pulse compression

Metal waveguide can be used as a dispersive medium to convert long duration, lower power pulses into short, higher peak power pulses. This provides an advanced method to generate radiation with gigawatts power in the millimeter and sub-millimeter wavelength range by compressing a megawatt level long duration pulse. In this paper, a five-fold helically corrugated waveguide operating in X-band was designed and constructed. The experiments conducted show that a 5.75 kW average power microwave pulse with a 6% bandwidth and duration of 80 ns can be compressed into a 144.8 kW, 1.6 ns pulse with a power compression factor of 25.2

Measurement of the Michel Parameters in Leptonic Tau Decays

The Michel parameters of the leptonic tau decays are measured using the OPAL detector at LEP. The Michel parameters are extracted from the energy spectra of the charged decay leptons and from their energy-energy correlations. A new method involving a global likelihood fit of Monte Carlo generated events with complete detector simulation and background treatment has been applied to the data recorded at center-of-mass energies close to sqrt(s) = M(Z) corresponding to an integrated luminosity of 155 pb-1 during the years 1990 to 1995. If e-mu universality is assumed and inferring the tau polarization from neutral current data, the measured Michel parameters are extracted. Limits on non-standard coupling constants and on the masses of new gauge bosons are obtained. The results are in agreement with the V-A prediction of the Standard Model.Comment: 32 pages, LaTeX, 9 eps figures included, submitted to the European Physical Journal

First Measurement of Z/gamma* Production in Compton Scattering of Quasi-real Photons

We report the first observation of Z/gamma* production in Compton scattering of quasi-real photons. This is a subprocess of the reaction e+e- to e+e-Z/gamma*, where one of the final state electrons is undetected. Approximately 55 pb-1 of data collected in the year 1997 at an e+e- centre-of-mass energy of 183 GeV with the OPAL detector at LEP have been analysed. The Z/gamma* from Compton scattering has been detected in the hadronic decay channel. Within well defined kinematic bounds, we measure the product of cross-section and Z/gamma* branching ratio to hadrons to be (0.9+-0.3+-0.1) pb for events with a hadronic mass larger than 60 GeV, dominated by (e)eZ production. In the hadronic mass region between 5 GeV and 60 GeV, dominated by (e)egamma* production, this product is found to be (4.1+-1.6+-0.6) pb. Our results agree with the predictions of two Monte Carlo event generators, grc4f and PYTHIA.Comment: 18 pages, LaTeX, 5 eps figures included, submitted to Physics Letters