Entanglement and Sources of Magnetic Anisotropy in Radical Pair-Based Avian Magnetoreceptors

One of the principal models of magnetic sensing in migratory birds rests on the quantum spin-dynamics of transient radical pairs created photochemically in ocular cryptochrome proteins. We consider here the role of electron spin entanglement and coherence in determining the sensitivity of a radical pair-based geomagnetic compass and the origins of the directional response. It emerges that the anisotropy of radical pairs formed from spin-polarized molecular triplets could form the basis of a more sensitive compass sensor than one founded on the conventional hyperfine-anisotropy model. This property offers new and more flexible opportunities for the design of biologically inspired magnetic compass sensors

Settlers in Earthquake Country: Apprehending Instability in New Zealand and California

This article examines how settlers in New Zealand and California responded to seismic instability throughout the late nineteenth century. By interpreting a series of moments during which the foundations of settlement were shaken by earthquakes I argue that the economic temporality of colonial boom and bust inflected contemporary understandings of natural disaster. In earthquake country, the relationships between scientists and settlers, their environmental knowledge, and the physical world existed in a dynamic equilibrium. When earthquakes struck in opportune conditions settlers were quick to resume their speculation on land, scientists were inspired by upheaval, and artists found sublimity in instability. In times of doubt earthquakes induced a latent anxiety among settlers about the prospects of the colonial project. In this context natural disasters were framed as threats to growth or harbingers of decline. Read together, responses to earthquakes offer a new way into the environmental history of settler colonialism that places a form of creative destruction at the center of the colonial project on both sides of the Pacific Rim

Capturing terra incognita: Alfred burton, ‘maoridom’ and wilderness in the king country

Across the settler colonies of the late nineteenth century the placemaking projects of newcomers were imbricated with Indigenous dispossession. Settler colonialism was, above all, a spatial project, and while the social and legal innovations of settler invasion have attracted substantial scholarly attention over the past two decades, its environmental dimensions remain insufficiently explored. Settler colonial studies might make more of its spatial turn. Through a close reading of the work of the Dunedin photographer Alfred Burton this article shows that visions of nature were the product of a system that managed continuing Indigenous presence by developing new conventions of representation. These practices divided Indigenous people from the landscapes that they inhabited, embellished settler environmental transformations, and contrived new natures. This article draws environmental history and settler colonial studies together to better understand the shared spatial foundations of Indigenous dispossession and settler placemaking

Asymmetric recombination and electron spin relaxation in the semiclassical theory of radical pair reactions

We describe how the semiclassical theory of radical pair recombination reactions recently introduced by two of us [D. E. Manolopoulos and P. J. Hore, J. Chem. Phys. 139, 124106 (2013)] can be generalised to allow for different singlet and triplet recombination rates. This is a non-trivial generalisation because when the recombination rates are different the recombination process is dynamically coupled to the coherent electron spin dynamics of the radical pair. Furthermore, because the recombination operator is a two-electron operator, it is no longer sufficient simply to consider the two electrons as classical vectors: one has to consider the complete set of 16 two-electron spin operators as independent classical variables. The resulting semiclassical theory is first validated by comparison with exact quantum mechanical results for a model radical pair containing 12 nuclear spins. It is then used to shed light on the spin dynamics of a carotenoid-porphyrin-fullerene (CPF) triad containing considerably more nuclear spins which has recently been used to establish a 'proof of principle' for the operation of a chemical compass [K. Maeda et al., Nature 453, 387 (2008)]. We find in particular that the intriguing biphasic behaviour that has been observed in the effect of an Earth-strength magnetic field on the time-dependent survival probability of the photo-excited C+PF- radical pair arises from a delicate balance between its asymmetric recombination and the relaxation of the electron spin in the carotenoid radical

Spin-selective reactions of radical pairs act as quantum measurements

Since the 1970s, spin-selective reactions of radical pairs have been modelled theoretically by adding phenomenological rate equations to the quantum mechanical equation of motion of the radical pair spin density matrix. Here, using a quantum measurement approach, we derive an alternative set of rate expressions which predict a faster decay of coherent superpositions of the singlet and triplet radical pair states. The difference between the two results, however, is not dramatic and would probably be difficult to distinguish experimentally from decoherence arising from other sources.Comment: Chemical Physics Letters, in press. 17 pages including 2 figues; pdf onl

ENVIRONMENTAL ACCOUNTS: TIME SERIES + ECO-TAXES

This study was commissioned by the European Commission in cooperation with Eurostat with the objective of improving and extending the scope of the environmental accounts for Ireland. It follows two previous studies, Pilot Environmental Accounts published by the Central Statistics Office and the Satellite Environmental Accounts for Ireland 1996, unpublished report to Eurostat (2000). As indicated in the title, this study presents time series, which in some cases are of considerable length, and provides information on what could loosely be called eco-taxes. Additionally, where feasible the study relates environmental information to the underlying economic magnitudes and movements, and broadens the information considerably. The report consists of three self-contained sections. The sections cover (1) emissions to air, (2) discharges to water and (3) disposals of solid waste and these three types of releases to the environment are disaggregated according to NACE Rev 1 by five major economic sectors: Agriculture/forestry/fishing Energy transformation Industry Transport Services Households though in some areas the breakdown is unavoidably less detailed and it is more detailed in others. Section 1 on emissions to air concentrates on greenhouse gases and on improving the underlying information on energy use. Behavioural analyses have been hampered in the past by inadequate time-series of energy-related prices and taxes so that a large effort was devoted here to presenting coherent time-series of these items

Reaction operators for spin-selective chemical reactions of radical pairs

Spin-selective reactions of radical pairs have traditionally been modelled theoretically by adding phenomenological rate equations to the quantum mechanical equation of motion of the radical pair spin density matrix. More recently an alternative set of rate expressions, based on a quantum measurement approach, has been suggested. Here we show how these two reaction operators can be seen as limiting cases of a more general reaction scheme.Comment: 10 pages, pdf from MS Word. Chem. Phys. Lett. (in press

Time evolution of spin state of radical ion pair in microwave field: An analytical solution

The paper reports an exact solution for the problem of spin evolution of radical ion pair in static magnetic and resonant microwave field taking into account Zeeman and hyperfine interactions and spin relaxation. The values of parameters that provide one of the four possible types of solution are analysed. It is demonstrated that in the absence of spin relaxation, besides the zero field invariant an invariant at large amplitudes of the resonant microwave field can be found. The two invariants open the possibility for simple calculation of microwave pulses to control quantum state of the radical pair. The effect of relaxation on the invariants is analysed and it is shown that changes in the high field invariant are induced by phase relaxation.Comment: 18 pages, 7 figure

Orientation of birds in radiofrequency fields in the absence of the Earth’s magnetic field: a possible test for the radical pair mechanism of magnetoreception

The magnetic compass sense of migratory songbirds is thought to derive from magnetically sensitive photochemical reactions in cryptochromes located in photoreceptor cells in the birds’ retinas. More specifically, transient radical pairs formed by light-activation of these proteins have been proposed to account for the birds’ ability to orient themselves using the Earth’s magnetic field and for the observation that radiofrequency magnetic fields, superimposed on the Earth’s magnetic field, can disrupt this ability. Here, by means of spin dynamics simulations, we show that it may be possible for the birds to orient in a monochromatic radiofrequency field in the absence of the Earth’s magnetic field. If such a behavioural test were successful, it would provide powerful additional evidence for a radical pair mechanism of avian magnetoreception