Twist and writhe dynamics of stiff filaments

This letter considers the dynamics of a stiff filament, in particular the coupling of twist and bend via writhe. The time dependence of the writhe of a filament is $W_r^2\sim L t^{1/4}$ for a linear filament and $W_r^2\sim t^{1/2} / L$ for a curved filament. Simulations are used to study the relative importance of crankshaft motion and tube like motion in twist dynamics. Fuller's theorem, and its relation with the Berry phase, is reconsidered for open filamentsComment: 7 Pages with 2 figure

Elasticity model of a supercoiled DNA molecule

Within a simple elastic theory, we study the elongation versus force characteristics of a supercoiled DNA molecule at thermal equilibrium in the regime of small supercoiling. The partition function is mapped to the path integral representation for a quantum charged particle in the field of a magnetic monopole with unquantized charge. We show that the theory is singular in the continuum limit and must be regularised at an intermediate length scale. We find good agreement with existing experimental data, and point out how to measure the twist rigidity accurately.Comment: Latex, 4 pages. The figure contains new experimental data, giving a new determination of the twist rigidit

Impact of the Berlin Accord and European Enlargement on Dairy Markets, The

Using a world agricultural model, we analyze the impact on dairy markets of the Berlin Accord on the European Union (EU) Common Agricultural Policy (CAP) Reforms. We also investigate the consequences of enlargement of the EU to include the Czech Republic, Hungary and Poland for the same markets. We produce a market outlook up to 2010 for these two scenarios. The Berlin Accord induces lower EU milk and dairy prices. A change in relative prices between cheese and butter-skim milk powder (SMP) occurs after 2005 and induces an expansion of cheese production, consumption and exports at the expense of the butterï¾–SMP sector. Accession of the three central and eastern European countries (CEECs) leads to a permanent but moderate decrease in EU prices of milk and dairy products. For the three acceding CEECs, domestic prices increase dramatically. Their final consumption of milk decreases and dairy product consumption drops considerably. The derived demand of milk in dairy production increases, however, because of the higher prices for dairy products, benefiting dairy producers in these CEECs. Dairy exports of the three acceding countries to the EUï¾–15 increase by one to three orders of magnitude, despite building large inventories. The impact of accession on world markets is small.

Writhing Photons and Berry Phases in Diffusive Wave Scattering

We study theoretically the polarization state of light in multiple scattering media in the limit of weak gradients in refractive index. Linearly polarized photons are randomly rotated due to the Berry phase associated with the scattering path. For circularly polarized light independent speckle patterns are found for the two helical states. The statistics of the geometric phase is related to the writhe distribution of semiflexible polymers such as DNA.Comment: 4 pages, 1 figur

Starsat: A space astronomy facility

Preliminary design and analyses of a versatile telescope for Spacelab missions are presented. The system is an all-reflective Korsch three-mirror telescope with excellent performance characteristics over a wide field and a broad spectral range, making it particularly suited for ultraviolet observations. The system concept is evolved around the utilization of existing hardware and designs which were developed for other astronomy space projects

Star formation in Perseus

We present a complete survey of current star formation in the Perseus molecular cloud, made at 850 and 450 micron with SCUBA at the JCMT. Covering 3 deg^2, this submillimetre continuum survey for protostellar activity is second in size only to that of rho Ophiuchus (Johnstone et al. 2004). Complete above 0.4 msun (5 sigma detection in a 14'' beam), we detect a total of 91 protostars and prestellar cores. Of these, 80% lie in clusters, representative of star formation across the Galaxy. Two of the groups of cores are associated with the young stellar clusters IC348 and NGC1333, and are consistent with a steady or reduced star formation rate in the last 0.5 Myr, but not an increasing one. In Perseus, 40--60% of cores are in small clusters (< 50 msun) and isolated objects, much more than the 10% suggested from infrared studies. Complementing the dust continuum, we present a C^18O map of the whole cloud at 1' resolution. The gas and dust show filamentary structure of the dense gas on large and small scales, with the high column density filaments breaking up into clusters of cores. The filament mass per unit length is 5--11 msun per 0.1 pc. Given these filament masses, there is no requirement for substantial large scale flows along or onto the filaments in order to gather sufficient material for star formation. We find that the probability of finding a submillimetre core is a strongly increasing function of column density, as measured by C^18O integrated intensity, prob(core) proportional to I^3.0. This power law relation holds down to low column density, suggesting that there is no A_v threshold for star formation in Perseus, unless all the low-A_v submm cores can be demonstrated to be older protostars which have begun to lose their natal molecular cloud.Comment: 15 pages, 5 figures, bibtex file scubasf_astroph.bbl, included tex files SSA-clusters-sorted-tidy.te

The benefits of organic farming for biodiversity

Previous studies suggest widespread positive responses of biodiversity to organic farming. Many of these studies, however, have been small-scale. This project tested the generality of habitat and biodiversity differences between matched pairs of organic and non-organic farms containing cereal crops in lowland England on a large-scale across a range of taxa including plants, insects, birds and bats. The extent of both cropped and un-cropped habitats together with their composition and management on a range of scales were also compared. Organic farms was likely to favour higher levels of biodiversity and indeed organic farms tended to support higher numbers of species and overall abundance across most taxa. However, the magnitude of the response differed strikingly; plants showed stronger and more consistent responses than other taxa. Some, but not all, differences in biodiversity between systems appear to be a consequence of differences in habitat quantity

The Impact of The European Enlargement and CAP Reforms on Agricultural Markets. Much Ado about Nothing?

We analyze the effects of the 2004 CAP reform and EU enlargement on European and world agricultural markets. We compare the results from a CAP reform only and a CAP reform plus enlargement scenarios to a no-enlargement baseline implementing Agenda 2000 CAP policies. We utilize the Food and Agricultural Policy Research Institute's policy analysis model to simulate the effects of CAP reform and EU enlargement on production, consumption, and trade for the EU, its New Member States (NMS), and major players in world agricultural markets. The model is a partial-equilibrium model of world agricultural markets including important producer and consumer countries in world livestock and products, dairy, grains, oilseeds and products, cotton and sugar markets. Each country's commodity sectors are modeled with structural equations which incorporate all important policy parameters. With prices in most commodities in the NMS historically below EU-15 prices accession leads to substantial price increases for many commodities in the NMS. Higher prices stimulate production and dampen consumption in the NMS, and trade between the new members and the EU-15 increases. Prices in the EU-15 decrease moderately. The impact of the two reforms on world markets is negligible. The CAP reforms have their greatest impact in the EU-15 markets for meats, rice, rapeseed, and dairy products. CAP reforms without enlargement generate a small increase in world and EU commodity prices.CAP, trade reform, policy reform, enlargement, new member states, European Union, Agricultural and Food Policy, Marketing, F1, Q17, Q18,

Elastic constants of beta-eucryptite: A density functional theory study

The five independent elastic constants of hexagonal $\beta$-eucryptite have been determined using density functional theory (DFT) total energy calculations. The calculated values agree well, to within 15%, with the experimental data. Using the calculated elastic constants, the linear compressibility of $\beta$-eucryptite parallel to the c-axis, $\chi_c$, and perpendicular to it, $\chi_a$, have been evaluated. These values are in close agreement to those obtained from experimentally known elastic constants, but are in contradiction to the direct measurements based on a three-terminal technique. The calculated compressibility parallel to the c-axis was found to positive as opposed to the negative value obtained by direct measurements. We have demonstrated that $\chi_c$ must be positive and discussed the implications of a positive $\chi_c$ in the context of explaining the negative bulk thermal expansion of $\beta$-eucryptite.Comment: 3 eps figures, submitted for publicatio

The measurement of low pay in the UK labour force survey

Consideration of the National Minimum Wage requires estimates of the distribution of hourly pay. The UK Labour Force Survey (LFS) is a key source of such estimates. The approach most frequently adopted by researchers has been to measure hourly earnings from several questions on pay and hours. The Office for National Statistics is now applying a new approach, based on an alternative more direct measurement introduced in March 1999. These two measures do not produce identical values and this paper investigates sources of discrepancies and concludes that the new variable is more accurate. The difficulty with using the new variable is that it is only available on a subset of respondents. An approach is developed in which missing values of the new variable are replaced by imputed values. The assumptions underlying this imputation approach and results of applying it to LFS data are presented. The relation to weighting approaches is also discussed