Of Rocks and Revolutions

This post is part of a series featuring behind-the-scenes dispatches from our Pohanka Interns on the front lines of history this summer as interpreters, archivists, and preservationists. See here for the introduction to the series. It is difficult to explain how the most advanced military technology of the 18th century relies upon a rock to function. Examined with modern eyes, the flintlock musket is as absurd as the macaroni fashion of the era. A petite vise grips a hunk of flint, which when thrown upon a steel battery, showers sparks on a criminally unmeasured amount of black powder. This produces a blinding flash, ushering a jet of flame through an eighth inch wide hole in the barrel. The powder condensed behind the ounce ball of lead is transformed from inert sulfur, charcoal and potassium nitrate into instant leviathan strength. The bullet careens down the barrel until its ejection from the twelve gauge bore, destined for whatever organic matter may halt the progress of this thoroughly unnatural reaction. [excerpt

They Were Only Playin\u27 Leapfrog! : The Infantryman and the Staff Officer in the British Army in the Great War

The British Infantryman of the First World War hated Staff Officers more than any other supporting or service branch in the BEF. This essay explores this attitude, its motivations, and the ways complaining helped British Infantrymen endure the Great War. It argues that the British Infantryman felt separate from the Staff Officers because of his intimate understanding of combat and killing and manifested his frustration with the helpless circumstances of war by hating Staff Officers, but ultimately understood the Staff Officer\u27s role and the necessity of their service. By reconsidering the hackneyed views of the \u27Poor Bloody Infantry\u27 a new source of endurance is identified

Rigorous Quantum Limits on Monitoring Free Masses and Harmonic Oscillators

There are heuristic arguments proposing that the accuracy of monitoring position of a free mass $m$ is limited by the standard quantum limit (SQL):$\sigma^2 (X(t)) \geq \sigma^2 (X(0)) +(t^2/m^2) \sigma^2 (P(0))\geq \hbar t/m$, where $\sigma^2 (X(t))$ and $\sigma^2 (P(t))$ denote variances of the Heisenberg representation position and momentum operators. Yuen discovered that there are contractive states for which this result is incorrect. Here I prove universally valid rigorous quantum limits (RQL) viz. rigorous upper and lower bounds on $\sigma^2 (X(t))$ in terms of $\sigma^2 (X(0))$ and $\sigma^2 (P(0))$ for a free mass, and for an oscillator. I also obtain the `maximally contractive' and `maximally expanding' states which saturate the RQL, and use the contractive states to set up an Ozawa-type measurement theory with accuracies respecting the RQL but beating the standard quantum limit. The Contractive states for oscillators improve on the Schr\"odinger coherent states of constant variance and may be useful for gravitational wave detection and optical communication.Comment: 6 page

Application of Mechanical and Electronic Devices to Legal Literature

published or submitted for publicatio

On the Z2Z_2 classification of Quantum Spin Hall Models

We propose an alternative formulation of the $Z_2$ topological index for quantum spin Hall systems and band insulators when time reversal invariance is not broken. The index is expressed in terms of the Chern numbers of the bands of the model, and a connection with the number of pairs of robust edge states is thus established. The alternative index is easy to compute in most cases of interest. We also discuss connections with the recently proposed spin Chern number for quantum spin Hall models.Comment: Presentation changed to improve clarity, some technical aspects of the topological arguments including material previously cited as unpublished notes have now been added as an appendi

Improved method of fabricating planar gallium arsenide diodes

Improved method fabricates electroluminescent planar P-N gallium arsenide diodes. GaAs is masked with silicon monoxide to allow P-type impurities to be diffused into unmasked portions of GaAs to form P-N junctions

Analysis and modelling of a rotary forming process for cast aluminum alloy A356

Spinning of a common aluminum automotive casting alloy A356 (Al-7Si-0.3 Mg) at elevated temperatures has been investigated experimentally with a novel industrial-scale apparatus. This has permitted the implementation of a fully coupled thermomechanical finite element model aimed at quantifying the processing history (stress, strain, strain-rate and temperature) and predicting the final geometry. The geometric predictions of this model have been compared directly to the geometry of the workpieces obtained experimentally. This study is novel in regards to both the size and shape of the component as well as the constitutive material representation employed. The model predictions are in reasonable agreement with experimental results for small deformations, but errors increase for large deformation conditions. The model has also enabled the characterization of the mechanical state which leads to a common spinning defect. Suggestions for improving the accuracy and robustness of the model to provide a predictive tool for industry are discussed