Ion-Cyclotron Double Resonance

A charged particle in a uniform moving magnetic field H describes a circular orbit in a plance perpendicular to H with an angular frequency or "cyclotron frequency" omagae. When an alternating electric field E(t) is applied normal to H at omegae, the ions absorb energy from the alternating electric field, and are accelerated to larger velocities and orbital radii. [1] The absorption of energy from E(t) at the cyclotron resonance frequency can be conveniently detected using a marginal oscillator detector. When the ions accelerated by E(t) collide with other particles, they lose some of their excess energy. A mixture of ions and neutral molecules in the presence of H and E(t) then reaches a steady-state condition in which the energy gained by the ions from E(t) between collisions is lost to the neutral molecules in collisions

Analytic results for two-loop Yang-Mills

Recent Developments in computing very specific helicity amplitudes in two loop QCD are presented. The techniques focus upon the singular structure of the amplitude rather than on a diagramatic and integration approachComment: Talk presented at 13th International Symposium on Radiative Corrections, 24-29 September, 2017,St. Gilgen, Austria, 9 page

Constructing Gravity Amplitudes from Real Soft and Collinear Factorisation

Soft and collinear factorisations can be used to construct expressions for amplitudes in theories of gravity. We generalise the "half-soft" functions used previously to "soft-lifting" functions and use these to generate tree and one-loop amplitudes. In particular we construct expressions for MHV tree amplitudes and the rational terms in one-loop amplitudes in the specific context of N=4 supergravity. To completely determine the rational terms collinear factorisation must also be used. The rational terms for N=4 have a remarkable diagrammatic interpretation as arising from algebraic link diagrams.Comment: 18 pages, axodraw, Proof of eq. 4.3 adde

Improved strain-wire flowmeter has fast response time

Strain-sensitive resistance wires in a Wheatstone bridge arrangement form the sensing element of a flowmeter. The change in resistance of the wires is measured as a function of stream velocity. Thus the electrical output is a measure of both rapidly varying and steady fluid-flow rates

Fluctuations and Correlations in Lattice Models for Predator-Prey Interaction

Including spatial structure and stochastic noise invalidates the classical Lotka-Volterra picture of stable regular population cycles emerging in models for predator-prey interactions. Growth-limiting terms for the prey induce a continuous extinction threshold for the predator population whose critical properties are in the directed percolation universality class. Here, we discuss the robustness of this scenario by considering an ecologically inspired stochastic lattice predator-prey model variant where the predation process includes next-nearest-neighbor interactions. We find that the corresponding stochastic model reproduces the above scenario in dimensions 1< d \leq 4, in contrast with mean-field theory which predicts a first-order phase transition. However, the mean-field features are recovered upon allowing for nearest-neighbor particle exchange processes, provided these are sufficiently fast.Comment: 5 pages, 4 figures, 2-column revtex4 format. Emphasis on the lattice predator-prey model with next-nearest-neighbor interaction (Rapid Communication in PRE

Two-Loop Six Gluon All-Plus Helicity Amplitude

We present an analytic expression for the six-point all-plus helicity amplitude in QCD at two-loops. We compute the rational terms in a compact analytic form organised by their singularity structure

Two-loop n-point all-plus helicity amplitude

We propose a compact analytic expression for the polylogarithmic part of the $n$-point two-loop all-plus helicity amplitude in gauge theory

Countryside Survey: Headwater Streams Report from 2007

This technical report describes methods and results from the headwater streams component of Countryside Survey. Countryside Survey (CS) consists of a field-based survey of 591 1km x 1km sample squares spread across England, Scotland and Wales, undertaken approximately every eight years. Around 60% of these squares contain at least one linear water feature such as a stream or ditch. Surveys of a headwater stream or ditch/drain site have been undertaken as part of Countryside Survey in 1990, 1998 and 2007. Since 1998, the survey has consisted of three elements: the macroinvertebrates (small aquatic animals visible to the naked eye which live on the stream bed), the macrophytes (larger aquatic plants) and the habitats (the structure of the channel and riparian zone). A single water chemistry sample is taken for supporting information. In 1990, only the macroinvertebrate component of the survey was undertaken. Compared with larger rivers, headwater streams are relatively poorly covered by the monitoring of national agencies. The data collected in Countryside Survey allow for an integrated description of the changes in ecological status and biodiversity of headwater streams through time, and the description of these changes is the main aim of this report. Additionally, for macroinvertebrates, their status against a minimally-impacted reference condition may be assessed. The vast amount of data available for the terrestrial survey component of Countryside Survey allows many potential linkages to be examined between human activities and stream ecological response. In this report, we detail some of these linkages, which will be elaborated further as part of the Countryside Survey Integrated Assessment to be published later in 2010. Results show many areas of improvement over the period 1998 to 2007. Notable improvements have occurred to macroinvertebrate status indicators in England, although south east England in particular is starting from a lower baseline of headwater stream biological quality when compared to other parts of Great Britain. Numbers of sites at good or high macroinvertebrate status in south east lowland England are still relatively low (30%). Increases in the number of macrophyte species and habitat quality appear to have occurred throughout Great Britain. Finally, improvements to trophic (nutrient) status, as indicated by the macrophyte communities, have occurred in Scotland. Substantial improvements in macroinvertebrate indicators occurred between 1990 and 1998 for all parts of Great Britain, however part of this observed improvement may be due to drought conditions in 1990. Declines have been observed in macroinvertebrate status for the Scottish Highlands, which had the highest proportion of sites at good or high status in 1998, but in 2007 this proportion has dropped to a level comparable to that of the rest of Scotland and upland England. Unfortunately it is not currently possible to pinpoint causes of this decline. There is an indication of increased extent of resectioning (engineering of the channel to widen, deepen and straighten), particularly in lowland Scotland, however this may be due to this feature being better recorded in 2007 compared to 1998. The example from Scotland is unusual in that for other indices and countries, there is no evidence for differences in trends between Environmental Zones. Quantification of changes in Wales is limited by the smaller sample size. A provisional integrated assessment has linked land management characteristics taken from the Countryside Survey square containing each headwater streams site, to an indicator of stream biological quality based on the mean stress sensitivity score of the macroinvertebrate taxa present. This has indicated logical negative relationships between intensive land uses such as arable and improved grassland and ecological status. Indicators of management of the river channel, such as the extent of resectioning (for land drainage and flood defence purposes), are also negatively associated with ecological status. Characteristics of the riparian zone, such as the amount of woody cover, are positively associated with ecological status. Overall, the headwater streams component of Countryside Survey is now beginning to build up a picture of the changes occurring to the ecological status of headwater streams. The changes are broadly positive, although some negative changes will need further investigation. The Headwater Streams Report was produced by the Centre for Ecology and Hydrology CEH), with contributions by Queen Mary University of London (QMUL), and Bournemouth University (BU)

Inherited Twistor-Space Structure of Gravity Loop Amplitudes

At tree-level, gravity amplitudes are obtainable directly from gauge theory amplitudes via the Kawai, Lewellen and Tye closed-open string relations. We explain how the unitarity method allows us to use these relations to obtain coefficients of box integrals appearing in one-loop N=8 supergravity amplitudes from the recent computation of the coefficients for N=4 super-Yang-Mills non-maximally-helicity-violating amplitudes. We argue from factorisation that these box coefficients determine the one-loop N=8 supergravity amplitudes, although this remains to be proven. We also show that twistor-space properties of the N=8 supergravity amplitudes are inherited from the corresponding properties of N=4 super-Yang-Mills theory. We give a number of examples illustrating these ideas.Comment: 32 pages, minor typos correcte

Food storage facilitates professional religious specialization in hunter–gatherer societies

Professional religious specialists centralised religious authority in early human societies and represented some of the earliest instances of formalised social leadership. These individuals played a central role in the emergence of organised religion and transitions to more stratified human societies. Evolutionary theories highlight a range of environmental, economic and social factors that are potentially causally related to the emergence of professional religious specialists in human history. There remains little consensus over the relative importance of these factors and whether professional religious specialists were the outcome or driver of increased socio-cultural complexity. We built a global dataset of hunter–gatherer societies and developed a novel method of exploratory phylogenetic path analysis. This enabled us to systematically identify the factors associated with the emergence of professional religious specialists and infer the directionality of causal dependencies. We find that environmental predictability, environmental richness, pathogen load, social leadership and food storage systems are all correlated with professional religious specialists. However, only food storage is directly related to the emergence of professional religious specialists. Our findings are most consistent with the claim that the early stages of organised religion were the outcome rather than driver of increased socio-economic complexity.Introduction Methods and results Conclusio