Evolution of time preference by natural selection

We reexamine Rogers’ (1994) analysis of the biological basis of the rate of time preference. Although his basic insight concerning the derivation of the felicity function holds up, the functional form he uses does not generate the evolutionary equilibrium behavior. Moreover, Rogers relies upon an interior solution for a particular kind of intergenerational transfer. We show such interior solutions do not generally arise. Hence Rogers most striking prediction, namely that the real interest rate should be about 2% per annum, does not follow

Is friction responsible for the reduction of fusion rates far below the Coulomb barrier?

The fusion of two interacting heavy ions traditionally has been interpreted in terms of the penetration of the projectile into the target. Observed rates well below the Coulomb barrier are considerably lower than estimates obtained from penetration factors. One approach in the analysis of the data invokes coupling to non-elastic channels in the scattering as the source of the depletion. Another is to analyze those data in terms of tunneling in semi-classical models, with the observed depletion being taken as evidence of a ``friction'' under the barrier. A complementary approach is to consider such tunneling in terms of a fully quantal model. We investigate tunneling with both one-dimensional and three-dimensional models in a fully quantal approach to investigate possible sources for such a friction. We find that the observed phenomenon may not be explained by friction. However, we find that under certain conditions tunneling may be enhanced or diminished by up to 50%, which finds analogy with observation, without the invocation of a friction under the barrier.Comment: 18 pages, 15 figures embedde

Incoherent single pion electroproduction on the deuteron with polarization effects

Incoherent pion electroproduction on the deuteron is studied from threshold up to the second resonance region with special emphasis on the influence of final state interaction, in particular on polarization observables. The elementary $\gamma N\to\pi N$ amplitude is taken from the MAID-2003 model. Final state interaction is included by considering complete rescattering in the final $NN$ and $\pi N$ subsystems. Their influence on the structure functions governing the semi-exclusive differential cross section, where besides the scattered electron only the produced pion is detected, is investigated in detail. For charged pion-production the effect of $NN$-rescattering is moderate whereas $\pi N$-rescattering is almost negligible, except very close to threshold. $NN$-rescattering appears much stronger in neutral pion production for which the primary mechanism is the elimination of a significant spurious coherent contribution in the impulse approximation. Sizeable effects are also found in some of the polarization structure functions for beam and/or target polarizations.Comment: 20 pages including 14 figure

Last scattering, relic gravitons and the circular polarization of the CMB

The tensor contribution to the $V$-mode polarization induced by a magnetized plasma at last scattering vanishes exactly. Conversely a polarized background of relic gravitons cannot generate a $V$-mode polarization. The reported results suggest that, in the magnetized $\Lambda$CDM paradigm, the dominant source of circular dichroism stems from the large-scale fluctuations of the spatial curvature.Comment: 8 pages, no figure

Incoherent pion photoproduction on the deuteron with polarization observables I: Formal expressions

Formal expressions are developed for the general five-fold differential cross section of incoherent $\pi$-photoproduction on the deuteron including beam and target polarization. The polarization observables of the cross section are described by various beam, target and beam-target asymmetries for polarized photons and/or polarized deuterons. They are given as bilinear hermitean forms in the reaction matrix elements divided by the unpolarized cross section. In addition, the corresponding observables for the semi-exclusive reaction $\vec d(\vec \gamma,\pi)NN$ are also given.Comment: 11 pages, 1 figur

Parity of charged pions

This paper discusses the parity of charged pions. It is shown that the original determination of the parity of the negatively charged pion using the capture of negatively charged pions in deuterium to form two neutrons is not conclusive if the pion has

Reply to ``Comment on ``Lateral Casimir Force beyond the Proximity Force Approximation'' ''

We reply to the comment arXiv:quant-ph/0702060 on our letter arXiv:quant-ph/0603120 [Phys. Rev. Lett. 96, 100402 (2006)]Comment: 1 pag

Lateral Casimir force beyond the Proximity Force Approximation

We argue that the appropriate variable to study a non trivial geometry dependence of the Casimir force is the lateral component of the Casimir force, which we evaluate between two corrugated metallic plates outside the validity of the Proximity Force Approximation (PFA). The metallic plates are described by the plasma model, with arbitrary values for the plasma wavelength, the plate separation and the corrugation period, the corrugation amplitude remaining the smallest length scale. Our analysis shows that in realistic experimental situations the Proximity Force Approximation overestimates the force by up to 30%.Comment: 4 pages. Identical to v1, which was accidentally replaced by a different paper (quant-ph/0610026

Optical Non-Contact Railway Track Measurement with Static Terrestrial Laser Scanning to Better than 1.5mm RMS

The railway industry requires track to be monitored for a variety of reasons, particularly when any type of physical works take place within the vicinity of the asset (e.g. demolition, construction and redevelopment works). Terrestrial laser scanning (TLS) has considerable potential as a survey method for rail measurement due to its non-contact nature and independence from physical targeting at track level. The consensus from recently published work using static terrestrial laser scanning is that rail measurements to the order of 3mm RMS are routinely possible. Such measures are appropriate for extracting the gauge, cant and twist parameters required by the rail industry, however engineering specifications designed to ensure safe and comfortable running of the trains ideally require measurements of better quality. This paper utilises standard design rail profiles from the UK industry to optimise the way in which TLS point cloud data are fitted to the rail geometry. The work is based on the use of off the shelf phase-based TLS systems each capable of delivering single point measurements of the order of 5mm to cooperative surfaces. The paper describes a workflow which focuses the fitting process onto discrete planar rail elements derived from the design rail geometry. The planar fitting process is improved through understanding how data from these scanners respond to rail surfaces. Of particular importance is the removal of noisy data from the shiny running surfaces. Results from a sequence of multi-station TLS surveys of the same set of double tracks taken from platform level highlight the capability to obtain fits to the rail model of better than 1.5mm RMS. Whilst fitting can be carried out on a single side of a rail, the paper highlights the challenge of obtaining an accurate TLS registration necessary to extract both sides of each rail to the same level of accuracy. This configuration is proven over inter-TLS instrument separations of the order of 30m and demonstrates the TLS network coverage necessary to achieve such results even in the presence of an occluding electric third rail