Greenback-Gold Returns and Expectations of Resumption, 1862-1879

We propose a unified framework for studying the greenback-gold price during the U.S. suspension of convertibility from 1862 to 1879. The gold price is viewed as a floating exchange rate, with a fixed destination given by gold standard parity because of the prospect of resumption. We test this perspective using daily data for the entire period, and measure the effect of news during and after the Civil War. New evidence of a decline in the volatility of gold returns after the Resumption Act of 1875 provides statistical support for the importance of expectations of resumption.greenbacks, gold standard, regime switching

Greenback-gold returns and expectations of resumption, 1862 - 1879

We propose a unified framework for studying the greenback-gold price during the U.S. suspension of convertibility from 1862 to 1879. The gold price is viewed as a floating exchange rate, with a fixed destination given by gold standard parity because of the prospect of resumption. We test this perspective using daily data for the entire period, and measure the effect of news during and after the Civil War. New evidence of a decline in the volatility of gold returns after the Resumption Act of 1875 provides statistical support for the importance of expectations of resumption

Time-frequency analysis of ship wave patterns in shallow water: modelling and experiments

A spectrogram of a ship wake is a heat map that visualises the time-dependent frequency spectrum of surface height measurements taken at a single point as the ship travels by. Spectrograms are easy to compute and, if properly interpreted, have the potential to provide crucial information about various properties of the ship in question. Here we use geometrical arguments and analysis of an idealised mathematical model to identify features of spectrograms, concentrating on the effects of a finite-depth channel. Our results depend heavily on whether the flow regime is subcritical or supercritical. To support our theoretical predictions, we compare with data taken from experiments we conducted in a model test basin using a variety of realistic ship hulls. Finally, we note that vessels with a high aspect ratio appear to produce spectrogram data that contains periodic patterns. We can reproduce this behaviour in our mathematical model by using a so-called two-point wavemaker. These results highlight the role of wave interference effects in spectrograms of ship wakes.Comment: 14 pages, 7 figure

The changing UV and X-ray properties of the Of?p star CPD -28 2561

The Of?p star CPD -28 2561 was monitored at high energies with XMM-Newton and HST. In X-rays, this magnetic oblique rotator displays bright and hard emission that varies by ~55% with rotational phase. These changes occur in phase with optical variations, as expected for magnetically confined winds; there are two maxima and two minima in X-rays during the 73d rotational period of CPD -28 2561. However, contrary to previously studied cases, no significant hardness variation is detected between minima and maxima, with the exception of the second minimum which is slightly distinct from the first one. In the UV domain, broad-band fluxes remain stable while line profiles display large variations. Stronger absorptions at low velocities are observed when the magnetic equator is seen edge-on, which can be reproduced by a detailed 3D model. However, a difference in absorption at high velocities in the CIV and NV lines is also detected for the two phases where the confined wind is seen nearly pole-on. This suggests the presence of strong asymmetries about the magnetic equator, mostly in the free-flowing wind (rather than in the confined dynamical magnetosphere).Comment: 14 pages, 11 figures, accepted for publication by MNRA

Comment on "Hole-Burning Experiments within Glassy Models with Infinite Range Interactions"

Comment on: L.F. Cugliandolo and J.L. Iguain; Phys. Rev. Lett. {\bf 85} 3448 (2000)Comment: 1 page, RevTe

On the iterated Crank-Nicolson for hyperbolic and parabolic equations in numerical relativity

The iterated Crank-Nicolson is a predictor-corrector algorithm commonly used in numerical relativity for the solution of both hyperbolic and parabolic partial differential equations. We here extend the recent work on the stability of this scheme for hyperbolic equations by investigating the properties when the average between the predicted and corrected values is made with unequal weights and when the scheme is applied to a parabolic equation. We also propose a variant of the scheme in which the coefficients in the averages are swapped between two corrections leading to systematically larger amplification factors and to a smaller numerical dispersion.Comment: 7 pages, 3 figure

Nucleosynthesis and the variation of fundamental couplings

We determine the influence of a variation of the fundamental ``constants'' on the predicted helium abundance in Big Bang Nucleosynthesis. The analytic estimate is performed in two parts: the first step determines the dependence of the helium abundance on the nuclear physics parameters, while the second step relates those parameters to the fundamental couplings of particle physics. This procedure can incorporate in a flexible way the time variation of several couplings within a grand unified theory while keeping the nuclear physics computation separate from any model-dependent assumptions.Comment: 8 pages, no figure

Microrheology of microlitre samples: Probed with rotating optical tweezers

Microrheology is the study of fluid flows and material deformations on a microscopic scale. The study of viscoelasticity of microscopic structures, such as cells, is one application of microrheometry. Another application is to study biological and medical samples where only a limited volume (microlitres) of fluid is available. This second application is the focus of our work and we present a suitable microrheometer based on optical tweezers. Optical tweezers are an optical trap created by a tightly focused laser beam. The gradient force at this focus acts to trap transparent micron sized particles, which can be manipulated within the surrounding environment. We use the polarisation of the incident field to transfer angular momentum to a trapped spherical birefringent particle. This causes the particle to rotate and measuring the polarisation of the forward scattered light allows the optical torque applied to the sphere to be calculated. From the torque, the viscosity of the surrounding liquid can be found. We present a technique that allows us to perform these measurements on microlitre volumes of fluid. By applying a time-dependent torque to the particle, the frequency response of the liquid an also be determined, which allows viscoelasticity to be measured. This is left as a future direction for this project

A Constant Torque Micro-Viscometer

We present a technique to measure the viscosity of microscopic volumes of liquid using rotating optical tweezers. The technique can be used when only microlitre (or less) sample volumes are available, for example biological or medical samples, or to make local measurements in complicated micro-structures such as cells. The rotation of the optical tweezers is achieved using the polarisation of the trapping light to rotate a trapped birefringent spherical crystal, called vaterite. Transfer of angular momentum from a circularly polarised beam to the particle causes the rotation. The transmitted light can then be analysed to determine the applied torque to the particle and its rotation rate. The applied torque is determined from the change in the circular polarisation of the beam caused by the vaterite and the rotation rate is used to find the viscous drag on the rotating spherical particle. The viscosity of the surrounding liquid can then be determined. Using this technique we measured the viscosity of liquids at room temperature, which agree well with tabulated values. We also study the local heating effects due to absorption of the trapping laser beam. We report heating of 50-70 K/W in the region of liquid surrounding the particle