12,923 research outputs found
The Effect of Foot and Mouth Disease on Trade and Prices in International Beef Markets
The paper develops and uses a two step quantitative model to analyze the effect of Foot and Mouth Disease (FMD) on international beef markets over time. Using monthly data from 1990-2002 for 7 major beef exporters and for 22 major beef importers, we use a probit equation to estimate the probability that country i exports to country j, taking account of foot and mouth status of exporter, sanitary policy of importer, beef quality, trade preferences, distance, and other factors affecting whether beef trade occurs. We then use OLS to estimate the export prices that are obtained for beef, taking account of beef quality, country per capita, trading preferences, region, per capita income, and a time trend, including terms to adjust for censorship in the first stage. Using the estimated equations, we compare the predicted change in trading partners and in the prices received by the two exporters in our sample that are not FMD free, Brazil and Uruguay, under the assumption that their status switches from having FMD to being FMD free. The model performs well. The results suggest that FMD continues to impede trade between many countries and does accordingly reduce the price received for beef from countries with FMD. Nonetheless, the "sanction" from FMD appears smaller than previously believed.International Relations/Trade,
Zero Landau level in folded graphene nanoribbons
Graphene nanoribbons can be folded into a double layer system keeping the two
layers decoupled. In the Quantum Hall regime folds behave as a new type of Hall
bar edge. We show that the symmetry properties of the zero Landau level in
metallic nanoribbons dictate that the zero energy edge states traversing a fold
are perfectly transmitted onto the opposite layer. This result is valid
irrespective of fold geometry, magnetic field strength and crystallographic
orientation of the nanoribbon. Backscattering suppression on the N=0 Hall
plateau is ultimately due to the orthogonality of forward and backward
channels, much like in the Klein paradox.Comment: Final published version, with supplementary material appendi
The bimetric variational principle for General Relativity
The bimetric variational principle is a subtle reinterpretation of general
relativity that assumes the spacetime connection to be generated by an
independent metric. Unlike the so called Palatini formalism that promotes the
connection into a fundamental field, the new variational principle results in a
physically distinct theory since the potential for the connection carries new
degrees of freedom. The connection-generating metric naturally allows also an
antisymmetric component. This sets torsion propagating! It is also shown here
that while in the most straightforward generalization of the Einstein-Hilbert
action the nonmetric degrees of freedom become ghosts, there exist very simple
actions which give rise to viable theories at the linearised level when
subjected to the bimetric variational principle. However, the non linear
interactions might bring unpleasant features like the Boulware-Deser ghost.
This remains to be explored since this new type of bimetric theories does not,
in principle, lie in the class of usual bimetric theories where non-linear
interactions inevitably come in with new ghost-like degrees of freedom.Comment: 5 pages, no figures. Version 2: corrected sign error, considerably
extended discussion
Intra- and inter-examiner Reliability of Direct Facial Soft Tissue Measurements Using Digital Calipers
Background: The objective of this study is to determine if facial soft tissue measurements using digital calipers can be reliably taken by the same examiner and by a large group of examiners. Materials and Methods: Ten examiners performed a set of 18 in-clinic measurements on 10 female and 10 male dental students using a digital caliper twice over a 3-week period. The intra-class correlation coefficient and the Shrout-Fleiss method were used for the statistical analysis. Results: Anthropometric intra-examiner reliability was high for all measurements (none fell below R = 0.934). However, inter-examiner reliability exhibited a wide range of values, some reliable (nasal width at widest nostrils [R = 0.922] and subnasale to upper lip [R = 0.926]), and others unreliable [base of nose (R = 0.590), mouth height (R = 0.585), and soft tissue B point to gnathion (R = 0.623)]. Conclusions: Soft tissue measurements of clearly identifiable points measured by the same examiner produced highly consistent, accurate and reliable measurements. Soft tissue points with poor definition resulted in average-to-poor reliabilities measurements
Multiprotein DNA looping
DNA looping plays a fundamental role in a wide variety of biological
processes, providing the backbone for long range interactions on DNA. Here we
develop the first model for DNA looping by an arbitrarily large number of
proteins and solve it analytically in the case of identical binding. We uncover
a switch-like transition between looped and unlooped phases and identify the
key parameters that control this transition. Our results establish the basis
for the quantitative understanding of fundamental cellular processes like DNA
recombination, gene silencing, and telomere maintenance.Comment: 11 pages, 4 figure
- …