General solution of an exact correlation function factorization in conformal field theory

We discuss a correlation function factorization, which relates a three-point function to the square root of three two-point functions. This factorization is known to hold for certain scaling operators at the two-dimensional percolation point and in a few other cases. The correlation functions are evaluated in the upper half-plane (or any conformally equivalent region) with operators at two arbitrary points on the real axis, and a third arbitrary point on either the real axis or in the interior. This type of result is of interest because it is both exact and universal, relates higher-order correlation functions to lower-order ones, and has a simple interpretation in terms of cluster or loop probabilities in several statistical models. This motivated us to use the techniques of conformal field theory to determine the general conditions for its validity. Here, we discover a correlation function which factorizes in this way for any central charge c, generalizing previous results. In particular, the factorization holds for either FK (Fortuin-Kasteleyn) or spin clusters in the Q-state Potts models; it also applies to either the dense or dilute phases of the O(n) loop models. Further, only one other non-trivial set of highest-weight operators (in an irreducible Verma module) factorizes in this way. In this case the operators have negative dimension (for c < 1) and do not seem to have a physical realization.Comment: 7 pages, 1 figure, v2 minor revision

Axigluons cannot explain the observed top quark forward-backward asymmetry

We study an SU(3)^2 axigluon model introduced by Frampton, Shu, and Wang to explain the recent Fermilab Tevatron observation of a significant positive enhancement in the top quark forward-backward asymmetry relative to standard model predictions. First, we demonstrate that data on neutral B_d-meson mixing excludes the region of model parameter space where the top asymmetry is predicted to be the largest. Keeping the gauge couplings below the critical value that would lead to fermion condensation imposes further limits at large axigluon mass, while precision electroweak constraints on the model are relatively mild. Furthermore, by considering an extension to an SU(3)^3 color group, we demonstrate that embedding the model in an extra-dimensional framework can only dilute the axigluon effect on the forward-backward asymmetry. We conclude that axigluon models are unlikely to be the source of the observed top quark asymmetry.Comment: 12 pages, 7 eps figures included. Minor changes to conform with published versio

The mission oriented terminal area simulation facility

The Mission Oriented Terminal Area Simulation (MOTAS) was developed to provide an ATC environment in which flight management and flight operations research studies can be conducted with a high degree of realism. This facility provides a flexible and comprehensive simulation of the airborne, ground-based and communication aspects of the airport terminal area environment. Major elements of the simulation are: an airport terminal area environment model, two air traffic controller stations, several aircraft models and simulator cockpits, four pseudo pilot stations, and a realistic air-ground communications network. MOTAS has been used for one study with the DC-9 simulator and a series of data link studies are planned in the near future

Multiple envelope stress response pathways are activated in an Escherichia coli strain with mutations in two members of the deda membrane protein family

We have reported that simultaneous deletion of two Escherichia coli genes, yqjA and yghB, encoding related and conserved inner membrane proteins belonging to the DedA protein family results in a number of intriguing phenotypes, including temperature sensitivity at 42°C, altered membrane lipid composition, and cell division defects. We sought to characterize these and other phenotypes in an effort to establish a function for this protein family in E. coli. Here, using reporter assays, we show that the major envelope stress response pathways Cpx, Psp, Bae, and Rcs are activated in strain BC202 (W3110; yqjA yghB) at the permissive growth temperature of 30°C. We previously demonstrated that 10mMMg2+, 400mMNaCl, and overexpression of tatABC are capable of restoring normal growth to BC202 at elevated growth temperatures. Deletion of the cpxR gene from BC202 results in the loss of the ability of these supplements to restore growth at 42°C. Additionally, we report that the membrane potential of BC202 is significantly reduced and that cell division and growth can be restored either by expression of the multidrug transporter MdfA from a multicopy plasmid or by growth at pH 6.0. Together, these results suggest that the DedA family proteins YqjA and YghB are required for general envelope maintenance and homeostasis of the proton motive force under a variety of growth conditions. © 2013, American Society for Microbiology

Using frost sensitive cover crops for timely nitrogen mineralisation and soil moisture management

Cover crops can be utilised to lower soil nitrate leaching. However, depending on the species grown and cover crop termination management this may lead to nitrogen (N) immobilisation and/or depletion of soil moisture available to the following cash crop, potentially impacting on crop yields. Cover crop management is also dependent on using herbicides to terminate growth prior to planting the next crop. We used an alternative method for cover crop termination by capitalising on plant senescence by frost in a multi-species cover crop established over-winter between wheat and maize. The cover crops accumulated greater quantities of N than the control. However, upon cover crop senescence due to cold temperatures, the partially terminated cover crop significantly increased topsoil available N from December to late February. This available N in the topsoil could be susceptible to leaching although this was not observed in our study. Cover crops did not have a significant prolonged effect on soil moisture over winter and late spring. The following maize yields were not significantly different between the control and cover crop treatment. Frost sensitive cover crop species could not be reliably terminated under a temperate climate, but provided a continuous supply of soil available N as the plants senesced. Depending on the soil moisture and weather conditions in the spring there could be a N leaching risk although this could be mitigated by establishing early spring crops

Rapid Evolution of Testis Size Relative to Sperm Morphology Suggests that Post-Copulatory Selection Targets Sperm Number in \u3cem\u3eAnolis\u3c/em\u3e Lizards

Post-copulatory sexual selection is thought to be responsible for much of the extraordinary diversity in sperm morphology across metazoans. However, the extent to which post-copulatory selection targets sperm morphology versus sperm production is generally unknown. To address this issue, we simultaneously characterized the evolution of sperm morphology (length of the sperm head, midpiece and flagellum) and testis size (a proxy for sperm production) across 26 species of Anolis lizards, a group in which sperm competition is likely. We found that the length of the sperm midpiece has evolved 2–3 times faster than that of the sperm head or flagellum, suggesting that midpiece size may be the most important aspect of sperm morphology with respect to post-copulatory sexual selection. However, testis size has evolved faster than any aspect of sperm morphology or body size, supporting the hypothesis that post-copulatory sexual selection acts more strongly upon sperm production than upon sperm morphology. Likewise, evolutionary increases in testis size, which typically indicate increased sperm competition, are not associated with predictable changes in sperm morphology, suggesting that any effects of post-copulatory selection on sperm morphology are either weak or variable in direction across anoles. Collectively, our results suggest that sperm production is the primary target of post-copulatory sexual selection in this lineage

Help-seeking behaviours, opportunistic treatment and psychological implications of adolescent acne: cross-sectional studies in schools and hospital outpatient departments in the UK

BACKGROUND: Acne vulgaris (acne) is a common adolescent skin condition. It is associated with negative psychological impacts and sufferers do not easily seek help, hence is undertreated. OBJECTIVES: We investigated the self-reported prevalence, severity and psychological sequelae of acne, together with assessing help-seeking behaviour and its barriers, in separate school and hospital samples. We explored opportunistic treatment by paediatricians. METHODS: Self-reported survey with participants drawn from: (1) 120 adolescents aged 13–18 in a London tertiary paediatric outpatient department and (2) 482 adolescents from two London schools, aged 11–18. Adolescents confidentially and anonymously completed a questionnaire (paper or online) and those with acne completed the Cardiff Acne Disability Index (CADI) questionnaire. OUTCOME MEASURES: To explore if acne is being addressed opportunistically in outpatient appointments and the behaviours associated with seeking help and psychological implications of acne. RESULTS: Acne prevalence was reported as 58.3% in the clinic and 42.3% in schools, with 34.3% and 20.6% of participants having moderate acne (MA) or severe acne (SA), respectively. The correlation between acne severity and CADI was significant (regression coefficient=4.86, p<0.005 (MA) and 9.08, p<0.005 (SA) in the hospital; 1.92, p<0.001 (MA) and 7.41, p<0.005 (SA) in schools). Severity of acne was associated with increased likelihood of seeing a doctor in both samples (OR=8.95, 2.79–28.70 (MA) in the clinic and 1.31, 1.30–2.90 (MA) and 3.89, 0.66–22.98 (SA) in the community). Barriers to help seeking included embarrassment and believing doctors were unapproachable. Doctors addressed acne opportunistically in 2.9% of the sample, although 16.7% of those with MA and SA wished their doctor had raised it. CONCLUSION: Acne is common and has negative psychological implications, correlating with severity. Young people often forego seeking help and hospital clinicians rarely address acne opportunistically. Further work is needed to investigate how to reduce barriers to help seeking for acne

Rotational Evolution During Type I X-Ray Bursts

The rotation rates of six weakly-magnetic neutron stars accreting in low-mass X-ray binaries have most likely been measured by Type I X-ray burst observations with RXTE. The nearly coherent oscillations detected during the few seconds of thermonuclear burning are most simply understood as rotational modulation of brightness asymmetries on the neutron star surface. We show that, as suggested by Strohmayer and colleagues, the frequency changes of 1-2 Hz observed during bursts are consistent with angular momentum conservation as the burning shell hydrostatically expands and contracts. We calculate how vertical heat propagation through the radiative outer layers of the atmosphere and convection affect the coherence of the oscillation. We show that the evolution of the rotational profile depends strongly on whether the burning layers are composed of pure helium or mixed hydrogen/helium. Our results help explain the absence (presence) of oscillations from hydrogen-burning (helium-rich) bursts that was found by Muno and collaborators. We investigate angular momentum transport within the burning layers and the recoupling of the burning layers with the star. We show that the Kelvin-Helmholtz instability is quenched by the strong stratification, and that mixing between the burning fuel and underlying ashes by the baroclinic instability does not occur. However, the baroclinic instability may have time to operate within the differentially rotating burning layer, potentially bringing it into rigid rotation.Comment: To appear in The Astrophysical Journal; minor corrections made to tables and figure