Qualitative Properties of Magnetic Fields in Scalar Field Cosmology

We study the qualitative properties of the class of spatially homogeneous Bianchi VI_o cosmological models containing a perfect fluid with a linear equation of state, a scalar field with an exponential potential and a uniform cosmic magnetic field, using dynamical systems techniques. We find that all models evolve away from an expanding massless scalar field model in which the matter and the magnetic field are negligible dynamically. We also find that for a particular range of parameter values the models evolve towards the usual power-law inflationary model (with no magnetic field) and, furthermore, we conclude that inflation is not fundamentally affected by the presence of a uniform primordial magnetic field. We investigate the physical properties of the Bianchi I magnetic field models in some detail.Comment: 12 pages, 2 figures in REVTeX format. to appear in Phys. Rev.

Size Doesn't Matter: Towards a More Inclusive Philosophy of Biology

notes: As the primary author, O’Malley drafted the paper, and gathered and analysed data (scientific papers and talks). Conceptual analysis was conducted by both authors.publication-status: Publishedtypes: ArticlePhilosophers of biology, along with everyone else, generally perceive life to fall into two broad categories, the microbes and macrobes, and then pay most of their attention to the latter. ‘Macrobe’ is the word we propose for larger life forms, and we use it as part of an argument for microbial equality. We suggest that taking more notice of microbes – the dominant life form on the planet, both now and throughout evolutionary history – will transform some of the philosophy of biology’s standard ideas on ontology, evolution, taxonomy and biodiversity. We set out a number of recent developments in microbiology – including biofilm formation, chemotaxis, quorum sensing and gene transfer – that highlight microbial capacities for cooperation and communication and break down conventional thinking that microbes are solely or primarily single-celled organisms. These insights also bring new perspectives to the levels of selection debate, as well as to discussions of the evolution and nature of multicellularity, and to neo-Darwinian understandings of evolutionary mechanisms. We show how these revisions lead to further complications for microbial classification and the philosophies of systematics and biodiversity. Incorporating microbial insights into the philosophy of biology will challenge many of its assumptions, but also give greater scope and depth to its investigations

Neutron scattering investigations of the partially ordered pyrochlore Tb2Sn2O7

Neutron scattering measurements have been performed on polycrystalline Tb2Sn2O7 at temperatures above and below that of the phase transition, TN 0.87 K, to investigate further the spin dynamics in the magnetically ordered state. In particular, new neutron spin echo results are presented showing a dependence on Q in the dynamics. We show evidence of the coexistence of static ferromagnetism and dynamically fluctuating spins down to 30 mK and we make a comparison of this partially ordered system to the spin liquid Tb2Ti2O

Low Energy Spin Dynamics In The Spin Ice Ho 2sn 2o 7

The magnetic properties of Ho 2Sn 2O 7have been investigated and compared to other spin ice compounds. Although the lattice has expanded by 3% relative to the better studied Ho 2Ti 2O 7spin ice, no significant changes were observed in the high temperature properties, T20K. As the temperature is lowered and correlations develop, Ho 2Sn 2O 7enters its quantum phase at a slightly higher temperature than Ho 2Ti 2O 7and is more antiferromagnetic in character. Below 80K a weak inelastic mode associated with the holmium nuclear spin system has been measured. The hyperfine field at the holmium nucleus was found to be 700T. © 2012 IOP Publishing Ltd.247Gardner, J.S., Gingras, M.J.P., Greedan, J.E., Magnetic pyrochlore oxides (2010) Rev. Mod. Phys., 82 (1), pp. 53-107Subramanian, M.A., Aravamudan, G., Subba Rao, G.V., Oxide pyrochloresa review (1983) Prog. 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Frustrated spin correlations in diluted spin ice Ho_2-x La_x Ti_2 O_7

We have studied the evolution of the structural properties as well as the static and dynamic spin correlations of spin ice Ho2Ti2O7, where Ho was partially replaced by non-magnetic La. The crystal structure of diluted samples Ho2-xLaxTi2O7 was characterized by x-ray and neutron diffraction and by Ho L-III-edge and Ti K-edge extended x-ray absorption fine structure (EXAFS) measurements. It is found that the pyrochlore structure remains intact until about x = 0.3, but a systematic increase in local disorder with increasing La concentration is observed in the EXAFS data, especially from the Ti K edge.Quasi-elastic neutron scattering and ac susceptibility measurements show that, in x <= 0.4 samples at temperatures above macroscopic freezing, the spin -spin correlations are short ranged and dynamic in nature. The main difference with pure spin ice in the dynamics is the appearance of a second, faster, relaxation process

Polarized inelastic neutron scattering of the partially ordered Tb2Sn2O7

We present inelastic neutron scattering results on the geometrically frustrated pyrochlore Tb2Sn2O7. At high temperature T gt;50K, this system resembles the cooperative paramagnet Tb2Ti2O7, while at low temperature T 60mK, it displays remarkably different behavior. Powder neutron scattering, susceptibility and specific heat techniques have shown that below 0.87K Tb2Sn2O7 enters a partially ordered state that is characterized by two sublattice ferrimagnetic long range order which coexists with paramagnetic spin components. We show that i the low temperature state produces a large internal field and collective excitations and ii the coexisting paramagnetic state persists down to 0.1K, with spins fluctuation at a rate greater than 0.04 THz, resulting in a diffuse magnetic background to the diffraction patterns. A low lying excitation at 1.2meV partially softens as short range correlations build up while cooling in the paramagnetic stat