10,820 research outputs found
The colour evolution of the process q q -> q q g
We calculate the soft anomalous dimension matrix for a five-parton process,
qq -> qqg. Considering different bases we unveil some interesting properties of
this matrix.Comment: 11 pages; calculation extended to general 5-parton kinematic
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Understanding the impact of volunteering on pro-environmental behavioural change
This article examines whether there is an association between engaging in environmental volunteering activities and pro-environmental behavioural change. Utilising self-reported surveys, the article explores the potential impact that environmental volunteering has on people's pro-environmental behaviours over time, using The Conservation Volunteers' two volunteering programmes â Green GymsÂź and Action Teams â as a comparative case study. The findings show a positive association between environmental volunteering activities and a person's self-reported pro-environmental behaviours over time. Further, volunteers presented improved impact across almost all of the eight pro-environmental behaviours measured, with differences observed between the two volunteering programmes as well as sociodemographic groupings
THE STRUCTURE FUNCTION F_2^{\gamma}(x,Q^2) AT LEP2
The unique nature of the photon can be investigated in hitherto unexplored
kinematic regions at LEP2. We discuss the theoretical significance of deep
inelastic measurements and present a prescription that allows a theoretically
and experimentally sensible separation of the so-called `anomalous' and
`hadronic' components of the target photon. We perform preliminary studies
regarding the ability to reconstruct the CM energy (and hence
) and the usefulness of the easier to measure electron structure function.Comment: 6 pages Latex + 5 figures in a uuencoded fil
Consistency between the radio and MIR faint source counts using the radio-MIR correlation
We show from the recent extrapolation of the radio-FIR correlation to the MIR
that the 20 cm and 15 um differential source counts are likely to come from the
same parent population.Comment: 2 pages, 2 figures, to appear in proceedings of 'Multi-wavelength AGN
surveys', Cozumel, 200
Breakdown of QCD coherence ?
We reconsider the calculation of a non-global QCD observable and find the
possible breakdown of QCD coherence. This breakdown arises as a result of wide
angle soft gluon emission developing a sensitivity to emission at small angles
and it leads to the appearance of super-leading logarithms. We use the `gaps
between jets' cross-section as a concrete example and illustrate that the new
logarithms are intimately connected with the presence of Coulomb gluon
contributions. Numerical estimates of their potential phenomenological
significance are presented.Comment: 7 pages, 3 figures; proceedings of Workshop on Diffraction in
High-Energy Physics - DIFFRACTION 2006, Sep. 5-10 2006, Adamantas, Milos
island, Greec
Under-dominance constrains the evolution of negative autoregulation in diploids
Regulatory networks have evolved to allow gene expression to rapidly track changes in the environment as well as to buffer perturbations and maintain cellular homeostasis in the absence of change. Theoretical work and empirical investigation in Escherichia coli have shown that negative autoregulation confers both rapid response times and reduced intrinsic noise, which is reflected in the fact that almost half of Escherichia coli transcription factors are negatively autoregulated. However, negative autoregulation is rare amongst the transcription factors of Saccharomyces cerevisiae. This difference is surprising because E. coli and S. cerevisiae otherwise have similar profiles of network motifs. In this study we investigate regulatory interactions amongst the transcription factors of Drosophila melanogaster and humans, and show that they have a similar dearth of negative autoregulation to that seen in S. cerevisiae. We then present a model demonstrating that this stiking difference in the noise reduction strategies used amongst species can be explained by constraints on the evolution of negative autoregulation in diploids. We show that regulatory interactions between pairs of homologous genes within the same cell can lead to under-dominance - mutations which result in stronger autoregulation, and decrease noise in homozygotes, paradoxically can cause increased noise in heterozygotes. This severely limits a diploid's ability to evolve negative autoregulation as a noise reduction mechanism. Our work offers a simple and general explanation for a previously unexplained difference between the regulatory architectures of E. coli and yeast, Drosophila and humans. It also demonstrates that the effects of diploidy in gene networks can have counter-intuitive consequences that may profoundly influence the course of evolution
Rapidity Gaps Between Jets
An excess of events with a rapidity gap between jets, over what would be
expected from non-diffractive processes, has been observed at HERA. A process
based on a perturbative QCD calculation of colour singlet exchange has been
added to HERWIG. With this addition, HERWIG is able to describe the number of
events with a gap between jets over the number without a gap. This gap fraction
is predicted to rise at large rapidity intervals between jets which would only
be visible if the detector coverage were increased.Comment: 5 pages including 3 figures. To appear in the conference proceedings
of the Workshop "Future Physics at HERA
Symmetry of anomalous dimension matrices explained
In a previous paper, one of us pointed out that the anomalous dimension
matrices for all physical processes that have been calculated to date are
complex symmetric, if stated in an orthonormal basis. In this paper we prove
this fact and show that it is only true in a subset of all possible orthonormal
bases, but that this subset is the natural one to use for physical
calculations.Comment: 4 page
The 12 ÎŒm ISO-ESO-Sculptor and 24 ÎŒm Spitzer faint counts reveal a population of ULIRGs as dusty massive ellipticals: Evolution by types and cosmic star formation
Context. Multi-wavelength galaxy number counts provide clues to the nature of galaxy evolution. The interpretation per galaxy type of
the mid-IR faint counts obtained with ISO and Spitzer, consistent with the analysis of deep UV-optical-near IR galaxy counts, provide
new constraints on the dust and stellar emission. Discovering the nature of new populations, such as high redshift ultra-luminous
(â„10^(12) L_â) infrared galaxies (ULIRGs), is also crucial for understanding galaxy evolution at high redshifts.
Aims. We first present the faint galaxy counts at 12 ÎŒm from the catalogue of the ISO-ESO-Sculptor Survey (ISO-ESS) published in a
companion article (Seymour et al. 2007a, A&A, 475, 791). They go down to 0.31 mJy after corrections for incompleteness. We verify
the consistency with the existing ISO number counts at 15 ÎŒm. Then we analyse the 12 ÎŒm (ISO-ESS) and the 24 ÎŒm (Spitzer) faint
counts, to constrain the nature of ULIRGs, the cosmic star formation history and time scales for mass buildup.
Methods. We show that the ânormalâ scenarios in our evolutionary code PĂGASE, which had previously fitted the deep UV-opticalnear
IR counts, are unsuccessful at 12 ÎŒm and 24 ÎŒm. We thus propose a new ULIRG scenario adjusted to the observed cumulative
and differential 12 ÎŒm and 24 ÎŒm counts and based on observed 12 ÎŒm and 25 ÎŒm IRAS luminosity functions and evolutionary
optical/mid-IR colours from PĂGASE.
Results. We succeed in simultaneously modelling the typical excess observed at 12 ÎŒm, 15 ÎŒm (ISO), and 24 ÎŒm (Spitzer) in the
cumulative and differential counts by only changing 9% of normal galaxies (1/3 of the ellipticals) into ultra-bright dusty galaxies
evolving as ellipticals, and interpreted as distant ULIRGs. These objects present similarities with the population of radio-galaxy hosts
at high redshift. No number density evolution is included in our models even if minor starbursts due to galaxy interactions remain
compatible with our results.
Conclusions. Higher spectral and spatial resolution in the mid-IR, together with submillimeter observations using the future Herschel
observatory, will be useful to confirm these results
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