Reverse mathematics and uniformity in proofs without excluded middle

We show that when certain statements are provable in subsystems of constructive analysis using intuitionistic predicate calculus, related sequential statements are provable in weak classical subsystems. In particular, if a $\Pi^1_2$ sentence of a certain form is provable using E-HA${}^\omega$ along with the axiom of choice and an independence of premise principle, the sequential form of the statement is provable in the classical system RCA. We obtain this and similar results using applications of modified realizability and the \textit{Dialectica} interpretation. These results allow us to use techniques of classical reverse mathematics to demonstrate the unprovability of several mathematical principles in subsystems of constructive analysis.Comment: Accepted, Notre Dame Journal of Formal Logi

Are speed enforcement cameras more effective than other speed management measures? The impact of speed management schemes on 30mph roads.

This paper presents the results of an evaluation of the impact of various types of speed management schemes on both traffic speeds and accidents. The study controls for general trends in accidents, regression-to-mean effects and migration, separately estimating the accident changes attributable to the impact of the schemes on traffic speed and on traffic volume. It was found that, when judged in absolute terms, all types of speed management scheme have remarkably similar effects on accidents, with an average fall in personal injury accidents of about 1 accident/km/year. In terms of the percentage accident reduction, however, engineering schemes incorporating vertical deflections (such as speed humps or cushions) offer the largest benefits: at 44%, the average reduction in personal injury accidents attributable to such schemes, is twice that at sites where safety cameras were used to control speeds (22%) and they were the only type of scheme to have a significant impact on fatal and serious accidents. Other types of engineering scheme (with a fall of 29% in personal injury accidents) were on average less effective in reducing accidents than schemes with vertical features but more effective than cameras. All types of scheme were generally effective in reducing speeds, with the largest reductions tending to be obtained with vertical deflections and the smallest with other types of engineering schemes

Heat transfer to a resonant pulsating air stream in a pipe

The effect on convective heat transfer of resonant, longitudinal oscillations superimposed on a turbulent mean flow in a pipe has been investigated relative to the equivalent steady flow. Theoretically it is shown that the effect of acoustic streaming velocities is negligible for the range of pulsation parameters, but that the oscillating velocity can generate changes in the time-mean flow diffusivity - the change in mean diffusivity can only be predicted if quasi-steady pulsations are assumed. Heat transfer coefficients for the mean flow are evaluated from the Energy equation, for fully established conditions, assuming quasi-steady oscillations. It is proposed that a frequency factor can be derived to relate experimental heat transfer to the quasi-steady predictions, and that the factor would be a function of Strouhal number only. Local heat transfer coefficients were measured for a constant heat flux supply to an oscillating air flow in a pipe. The pulsations were generated by a siren. It was shown that the centre-line velocity amplitudes could be predicted from inviscid flow theory using a mean velocity of sound. The range of the major parameters was: Diraensionless pulsation velocity 0.3 < B < 5 Strouhal number 0.5 < S < 10 Reynolds number 14,300 < Red < 31,250. For fully developed flow, the experimental results were related to the corresponding quasi-steady predictions by a function of Strouhal number. It was shown that the changes in heat transfer were due to changes in the mean diffusivity generated by the acoustic velocity. For a defined range of pulsation parameters, it is possible to predict local heat transfer coefficients under fully established conditions for a pulsating flow from the empirical frequency correction factor applied to the theoretical quasi-steady predictions

Exchange Narrowing Effects in the EPR Linewidth of Gd Diluted in Ce Compounds

Anomalous thermal behavior on the EPR linewidths of Gd impurities diluted in Ce compounds has been observed. In metals, the local magnetic moment EPR linewidth, \Delta H, is expected to increase linearly with the temperature. In contrast, in Ce_{x}La_{1-x}Os_{2} the Gd EPR spectra show a nonlinear increase. In this work, the mechanisms that are responsible for the thermal behavior of the EPR lines in Ce_{x}La_{1-x}Os_{2} are examined. We show that the exchange interaction between the local magnetic moments and the conduction electrons are responsible for the narrowing of the spectra at low temperatures. At high temperatures, the contribution to the linewidth of the exchange interaction between the local magnetic moments and the $Ce$ ions has an exponential dependence on the excitation energy of the intermediate valent ions. A complete fitting of the EPR spectra for powdered samples is obtained.Comment: 11 pages, 1 figur

Across the genres: how journalism is changing in the 1990s

Writing is the key element in the dissemination of information. Content is king, whether for online, radio, print, or multimedia journalism. Increasingly converging production and delivery technologies are blurring the distinction between print and broadcast journalism. This has consequences for the teaching of writing skils to university journalism students