456 research outputs found
The one-loop six-dimensional hexagon integral with three massive corners
We compute the six-dimensional hexagon integral with three non-adjacent
external masses analytically. After a simple rescaling, it is given by a
function of six dual conformally invariant cross-ratios. The result can be
expressed as a sum of 24 terms involving only one basic function, which is a
simple linear combination of logarithms, dilogarithms, and trilogarithms of
uniform degree three transcendentality. Our method uses differential equations
to determine the symbol of the function, and an algorithm to reconstruct the
latter from its symbol. It is known that six-dimensional hexagon integrals are
closely related to scattering amplitudes in N=4 super Yang-Mills theory, and we
therefore expect our result to be helpful for understanding the structure of
scattering amplitudes in this theory, in particular at two loops.Comment: 15 pages, 2 figure
The more we do, the less we gain? Balancing effort and efficacy in managing the Solidago gigantea invasion
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Psychological and nutritional correlates of objectively assessed physical activity in patients with anorexia nervosa
Background:
Physical activity (PA) plays a role in the course of anorexia nervosa (AN).
Objective:
To assess the association between PA, nutritional status and psychological parameters in patients with AN.
Method:
Using a wearable activity monitor, PA was assessed in 60 female AN inpatients, by step count and time spent in 4 metabolic equivalent (MET)-intensity levels: sedentary behaviour, light, moderate and vigorous PA. In addition, BMI, psychological (patient-reported outcome questionnaires) and nutritional parameters (body fat, energy and macronutrient intake) were assessed.
Results:
The study population spent little time in vigorous PA. BMI on admission and discharge was higher when more time was spent in sedentary behaviour, and lower with more time spent in light PA. Relationships between PA and patient-reported outcomes were weak and limited to an association between vigorous PA and compulsiveness. Low fat mass was associated with more time spent in light PA, while subjects with higher step counts showed less intake of energy, carbohydrates and fat.
Conclusion:
The relationship between inadequate food intake and increased PA in patients with AN requires further investigation
Notes on Conformal Invisibility Devices
As a consequence of the wave nature of light, invisibility devices based on
isotropic media cannot be perfect. The principal distortions of invisibility
are due to reflections and time delays. Reflections can be made exponentially
small for devices that are large in comparison with the wavelength of light.
Time delays are unavoidable and will result in wave-front dislocations. This
paper considers invisibility devices based on optical conformal mapping. The
paper shows that the time delays do not depend on the directions and impact
parameters of incident light rays, although the refractive-index profile of any
conformal invisibility device is necessarily asymmetric. The distortions of
images are thus uniform, which reduces the risk of detection. The paper also
shows how the ideas of invisibility devices are connected to the transmutation
of force, the stereographic projection and Escheresque tilings of the plane
A generation apart? Youth and political participation in Britain
Conventional wisdom holds that young people in Britain are alienated from politics, with some claiming that this reflects a wider crisis of legitimacy that should be met by initiatives to increase citizenship. This article addresses these areas, presenting both panel survey and focus group data from first-time voters. It concludes that, contrary to the findings from many predominantly quantitative studies of political participation, young people are interested in political matters, and do support the democratic process. However they feel a sense of anti-climax having voted for the first time, and are critical of those who have been elected to positions of political power. If they are a generation apart, this is less to do with apathy, and more to do with their engaged scepticism about ‘formal’ politics in Britain
Hopf algebras, coproducts and symbols: an application to Higgs boson amplitudes
We show how the Hopf algebra structure of multiple polylogarithms can be used
to simplify complicated expressions for multi-loop amplitudes in perturbative
quantum field theory and we argue that, unlike the recently popularized
symbol-based approach, the coproduct incorporates information about the zeta
values. We illustrate our approach by rewriting the two-loop helicity
amplitudes for a Higgs boson plus three gluons in a simplified and compact form
involving only classical polylogarithms.Comment: 46 page
Proximity induced metal/insulator transition in superlattices
The far-infrared dielectric response of superlattices (SL) composed of
superconducting YBaCuO (YBCO) and ferromagnetic La%
CaMnO (LCMO) has been investigated by ellipsometry. A drastic
decrease of the free carrier response is observed which involves an unusually
large length scale of d20 nm in YBCO and d10
nm in LCMO. A corresponding suppression of metallicity is not observed in SLs
where LCMO is replaced by the paramagnetic metal LaNiO. Our data suggest
that either a long range charge transfer from the YBCO to the LCMO layers or
alternatively a strong coupling of the charge carriers to the different and
competitive kind of magnetic correlations in the LCMO and YBCO layers are at
the heart of the observed metal/insulator transition. The low free carrier
response observed in the far-infrared dielectric response of the magnetic
superconductor RuSrGdCuO is possibly related to this effect
Large-scale physical mapping within the region 22q12.3-13.1 in meningioma
The lack of physical mapping data strongly restricts the analysis of the meningioma chromosomal region that was assigned to the bands 22q12.3-qter. Recently, we reported a new marker D22S16 for chromosome 22 that was assigned to the region 22q13-qter by in situ hybridization. Utilizing somatic cell hybrids we now sublocalized the marker D22S16 within the band region 22q12-13.1, thus placing it in the vicinity of the gene for the platelet derived growth factor (PDGFB). A physical map was established for the regions surrounding the PDGFB gene and the D22S16 marker. By means of pulsed-field gel electrophoresis (PFGE) D22S16 and PDGFB were found to be physically linked within 900 kb. We also identified two CpG clusters bordering the PDGFB gene. For the enzyme NotI, a variation of the PDGFB restriction pattern was found between different individuals. PFGE analysis of the two loci (PDFGB and D22S16) failed to identify major rearrangements in meningioma.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/29218/1/0000273.pd
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