Modern methods for the determination of polar motion and UT1

The applications and Doppler satellite observations, laser ranging to artificial satellites and the Moon, and astronomic radio interferometry to monitoring polar motion and Universal Time System 1 (UT1) are discussed. How and what each method is capable of measuring, fundamental limitations, and the present status of the developments of each method were reviewed. Evaluations of the various methods as candidates for the next generation international polar motion and UT1 monitoring service are summarized

Poly-essential and general Hyperelastic World (brane) models

This article provides a unified treatment of an extensive category of non-linear classical field models whereby the universe is represented (perhaps as a brane in a higher dimensional background) in terms of a structure of a mathematically convenient type describable as hyperelastic, for which a complete set of equations of motion is provided just by the energy-momentum conservation law. Particular cases include those of a perfect fluid in quintessential backgrounds of various kinds, as well as models of the elastic solid kind that has been proposed to account for cosmic acceleration. It is shown how an appropriately generalised Hadamard operator can be used to construct a symplectic structure that controles the evolution of small perturbations, and that provides a characteristic equation governing the propagation of weak discontinuities of diverse (extrinsic and extrinsic) kinds. The special case of a poly-essential model - the k-essential analogue of an ordinary polytropic fluid - is examined and shown to be well behaved (like the fluid) only if the pressure to density ratio $w$ is positive.Comment: 16 pages Latex, Contrib. to 10th Peyresq Pysics Meeting, June 2005: Micro and Macro Structures of Spacetim

Biologically fixed N2 as a source for the N2O production in a grass clover mixture, measured by 15N2

The contribution of biologically fixed dinitrogen (N2) to the nitrous oxide (N2O) production in grasslands is unknown. To assess the contribution of recently fixed N2 as a source of N2O and the transfer of fixed N from clover to companion grass, mixtures of white clover and perennial ryegrass were incubated for 14 days in a growth cabinet with a 15N2-enriched atmosphere (0.4 atom% excess). Immediately after labelling, half of the grass-clover pots were sampled for N2 fixation determination, whereas the remaining half were examined for emission of 15N labelled N2O for another eight days using a static chamber method. Biological N2 fixation measured in grass-clover shoots and roots as well as in soil constituted 342, 38 and 67 mg N m-2 d-1 at 16, 26 and 36 weeks after emergence, respectively. The drop in N2 fixation was most likely due to a severe aphid attack on the clover component. Transfer of recently fixed N from clover to companion grass was detected at 26 and 36 weeks after emergence and amounted to 0.7 ± 0.1 mg N m-2 d-1, which represented 1.7 ± 0.3 % of the N accumulated in grass shoots during the labelling period. Total N2O emission was 91, 416 and 259 μg N2O-N m-2 d-1 at 16, 26 and 36 weeks after emergence, respectively. Only 3.2 ± 0.5 ppm of the recently fixed N2 was emitted as N2O on a daily basis, which accounted for 2.1 ± 0.5 % of the total N2O-N emission. Thus, recently fixed N released via easily degradable clover residues appears to be a minor source of N2O

Greenhouse gas emissions from cultivation of energy crops – is it important?

Replacing fossil fuel-derived energy with biomass-derived energy is commonly emphasized as a means to reduce CO2 emissions. However, our study highlights the risk of large greenhouse gas emissions when wastes from bioenergy production are recycled as fertilizer for energy crops. Crop management affects the magnitude of these emissions, which in some cases negate a considerable fraction of the global warming savings associated with biofuels

No effect of cropping system on the greenhouse gas N2O

Organic farming is comparable to conventional in terms of field emissions of the strong greenhouse gas nitrous oxide (N2O). Our study points to the need for increased yields in organic farming as measure to reduced emissions per unit of produce

Why do people live apart together?

Interpretations of living apart together (LAT) have typically counter-posed 'new family form' versus 'continuist' perspectives. Recent surveys, however, construct LAT as a heterogeneous category that supports a 'qualified continuist' position – most people live apart as a response to practical circumstances or as a modern version of 'boy/girlfriend', although a minority represents something new in preferring to live apart more permanently. This article interrogates this conclusion by examining in depth why people live apart together, using a nationally representative survey from Britain and interview accounts from 2011. Our analysis shows that LAT as a category contains different sorts of relationship, with different needs and desires. While overall coupledom remains pivotal and cohabitation remains the goal for most, LAT allows people flexibility and room to manoeuvre in adapting couple intimacy to the demands of contemporary life. Hence, we suggest, LAT is both 'new' and a 'continuation'

Renormalisation of gravitational self interaction for wiggly strings

It is shown that for any elastic string model with energy density $U$ and tension $T$, the divergent contribution from gravitational self interaction can be allowed for by an action renormalisation proportional to $(U-T)^2$. This formula is applied to the important special case of a bare model of the transonic type (characterised by a constant value of the product $UT$) that represents the macroscopically averaged effect of shortwavelength wiggles on an underlying microscopic model of the Nambu-Goto type (characterised by $U=T$).Comment: 11 pages, Latex; original 8 page version extended to include estimates of relevant orders of magnitude. To be published in Physical Review,

Twistable mold for helicopter blades

Design is described of mold for fabrication of blades composed of sets of aerodynamic shells having same airfoil section characteristics but different distributions. Mold consists of opposing stacks of thin templates held together by long bolts. When bolts are loosened, templates can be set at different positions with respect to each other and then locked in place