Algebraic Topology of Calabi-Yau Threefolds in Toric Varieties

We compute the integral homology (including torsion), the topological K-theory, and the Hodge structure on cohomology of Calabi-Yau threefold hypersurfaces and complete intersections in Gorenstein toric Fano varieties. The methods are purely topological

Theory Challenges of the Accelerating Universe

The accelerating expansion of the universe presents an exciting, fundamental challenge to the standard models of particle physics and cosmology. I highlight some of the outstanding challenges in both developing theoretical models and interpreting without bias the observational results from precision cosmology experiments in the next decade that will return data to help reveal the nature of the new physics. Examples given focus on distinguishing a new component of energy from a new law of gravity, and the effect of early dark energy on baryon acoustic oscillations.Comment: 10 pages, 4 figures; minor changes to match J. Phys. A versio

Fermion absorption cross section of a Schwarzschild black hole

We study the absorption of massive spin-half particles by a small Schwarzschild black hole by numerically solving the single-particle Dirac equation in Painleve-Gullstrand coordinates. We calculate the absorption cross section for a range of gravitational couplings Mm/m_P^2 and incident particle energies E. At high couplings, where the Schwarzschild radius R_S is much greater than the wavelength lambda, we find that the cross section approaches the classical result for a point particle. At intermediate couplings we find oscillations around the classical limit whose precise form depends on the particle mass. These oscillations give quantum violations of the equivalence principle. At high energies the cross section converges on the geometric-optics value of 27 \pi R_S^2/4, and at low energies we find agreement with an approximation derived by Unruh. When the hole is much smaller than the particle wavelength we confirm that the minimum possible cross section approaches \pi R_S^2/2.Comment: 11 pages, 3 figure

New Techniques for Analysing Axisymmetric Gravitational Systems. 1. Vacuum Fields

A new framework for analysing the gravitational fields in a stationary, axisymmetric configuration is introduced. The method is used to construct a complete set of field equations for the vacuum region outside a rotating source. These equations are under-determined. Restricting the Weyl tensor to type D produces a set of equations which can be solved, and a range of new techniques are introduced to simplify the problem. Imposing the further condition that the solution is asymptotically flat yields the Kerr solution uniquely. The implications of this result for the no-hair theorem are discussed. The techniques developed here have many other applications, which are described in the conclusions.Comment: 30 pages, no figure

Reflection Symmetries for Multiqubit Density Operators

For multiqubit density operators in a suitable tensorial basis, we show that a number of nonunitary operations used in the detection and synthesis of entanglement are classifiable as reflection symmetries, i.e., orientation changing rotations. While one-qubit reflections correspond to antiunitary symmetries, as is known for example from the partial transposition criterion, reflections on the joint density of two or more qubits are not accounted for by the Wigner Theorem and are well-posed only for sufficiently mixed states. One example of such nonlocal reflections is the unconditional NOT operation on a multiparty density, i.e., an operation yelding another density and such that the sum of the two is the identity operator. This nonphysical operation is admissible only for sufficiently mixed states.Comment: 9 page

Soil health as an indicator of sustainable management

Population growth, a widening gap between the rich and poor, environmental degradation, and a re-evaluation of energy use and alternatives will shape life in the 21st century. We will be challenged to increase food supplies for a global population one-and-a-half to two times its current size. But as agricultural systems grow to meet the demands of more people, increased pressure will be placed on our natural resources: competition for land, water and energy resources from both urban and industrial sectors becomes more acute and the available land base remains static or shrinks. Under current practices increased food production will greatly increase inputs into agricultural production systems, thereby vastly increasing opportunity for environmental pollution and degradation and depletion of natural and non-renewable resources (Power, 1996). To sustain agriculture and the world for future generations, we must act now to develop production systems which rely less on non-renewable, petrochemical based resources; rely more on renewable resources from the sun for our food, fiber, and energy needs; and achieve the ecological intensification needed to meet the increased future food demand (Cassman, 1999). However, better coordination with natural processes for meeting our food and energy needs will likely require some life-style change to achieve the multiple goals of economic, ecological, and environmental sustainability. The condition of our soils ultimately determines human health by serving as the major medium for food and fiber production and a primary interface with the environment, influencing the quality of air we breathe and water we drink. Thus, there is a clear linkage between soil quality and human and environmental health. As such, the health of our soil resources is a primary indicator of the sustainability of our land management practices (Acton and Gregorich, 1995). In this special issue, summary findings of an international workshop on “Soil Health as an Indicator of Sustainable Land Management”, held June 24 and 25, 1999 at the GAIA Environmental Research and Education Center in Kifissia, Greece are presented. The objectives of this workshop were to highlight the central role of soil health in sustaining society and assuring future environmental stability and agricultural productivity and to identify critical issues and research and education needs as related to sustainable development. Oral presentations on the first day of this workshop were given by scientists and professionals from the USA, Canada, Germany, Greece, France, Moldova, Poland, Spain, and the UK. On the second day of the workshop, participants worked together in one large group and in three small break-out groups to identify critical issues in sustainable management and to define research and education needs to address these issues. The final product was the identification of high priority research and education needs for the sustainable management of agricultural land and of the management “strategies” needed to achieve sustainability. A major challenge to us as scientists is in finding ways to translate our science into practices that people of the land can embrace to sustain both themselves and the soils and environments on which we all depend

Spatial solitary-wave optical memory

We consider some features of spatial solitary-wave switching in a unidirectional ring cavity that is partially filled with a fast and saturably self-focusing nonlinear medium. Large (part-beam switched) solitary arrays are considered. It is found that prescribed binary patterns may be encoded in the duration of a single cavity transit and subsequently remain stable over thousands of transits. Beam interrupt allows pixels to be switched off in fewer than ten cavity transits. Pixel instabilities on an unpixelated beam are shown to arise from spatial solitary attractive forces and intensity gradients

Early Dark Energy Cosmologies

We propose a novel parameterization of the dark energy density. It is particularly well suited to describe a non-negligible contribution of dark energy at early times and contains only three parameters, which are all physically meaningful: the fractional dark energy density today, the equation of state today and the fractional dark energy density at early times. As we parameterize Omega_d(a) directly instead of the equation of state, we can give analytic expressions for the Hubble parameter, the conformal horizon today and at last scattering, the sound horizon at last scattering, the acoustic scale as well as the luminosity distance. For an equation of state today w_0 < -1, our model crosses the cosmological constant boundary. We perform numerical studies to constrain the parameters of our model by using Cosmic Microwave Background, Large Scale Structure and Supernovae Ia data. At 95% confidence, we find that the fractional dark energy density at early times Omega_early < 0.06. This bound tightens considerably to Omega_early < 0.04 when the latest Boomerang data is included. We find that both the gold sample of Riess et. al. and the SNLS data by Astier et. al. when combined with CMB and LSS data mildly prefer w_0 < -1, but are well compatible with a cosmological constant.Comment: 6 pages, 3 figures; references added, matches published versio

Challenges to pharmaceutical policymaking: lessons from Australia’s National Medicines Policy

Objective: National medicines policies (NMPs) provide a means for governments to achieve their objectives in relation to pharmaceuticals and other medicines. This research aimed to identify challenges to implementing the objectives of the Australian NMP from the perspective of key stakeholders. Methods: In 2012 and 2103, we conducted 30 semi-structured interviews with stakeholders involved in the discovery, clinical testing, regulation and funding of medicines in Australia. We asked participants to describe their careers and to give their opinions on specific issues surrounding drug development, clinical research, regulation and subsidisation in Australia. Data were analysed using Morse’s outline of the cognitive basis of qualitative research and Charmaz’s outline of data analysis in grounded theory. The initial phase of “open coding”, revealed findings that could be mapped to three of the four objectives of the NMP. We then conducted “focused coding” for themes relevant to these objectives. Results: Participants identified many issues relevant to the ongoing evolution of the NMP, relating primarily to ongoing tensions between the commercial objective of ensuring a viable medicines industry, and the non-commercial objectives of ensuring that medicines are safe, effective and affordable. There were also a number of other challenges identified to the achievement of both the commercial and non-commercial objectives of the NMP. These included limits to government funding, globalisation, consumer advocacy, changing scientific paradigms and new information technologies. Conclusions: There are many issues that need to be addressed if policymakers are to achieve the best outcomes from the NMP. Tensions between the commercial and non-commercial objectives of the NMP suggest the need to ensure that one stakeholder group’s imperatives do not stifle those of other groups. At the same time, there are a number of emerging issues that are likely to concern all stakeholders equally, and these are both challenges and opportunities for new kinds of collaboration