1,969 research outputs found
SUSY Ward identities for multi-gluon helicity amplitudes with massive quarks
We use supersymmetric Ward identities to relate multi-gluon helicity
amplitudes involving a pair of massive quarks to amplitudes with massive
scalars. This allows to use the recent results for scalar amplitudes with an
arbitrary number of gluons obtained by on-shell recursion relations to obtain
scattering amplitudes involving top quarks.Comment: 22 pages, references adde
Immediate effects of microclimate modification enhance native shrub encroachment
Shrubs have become more dense and expanded beyond their range all over the world for a variety of reasons including increased temperatures, overgrazing, and alteration of historical fire regime. Native shrubs have been encroaching on Virginia barrier island grasslands for over half a century for unknown reasons. Species composition, soil nutrients, leaf area index (LAI), and ground and air temperature were recorded across the shrub to grass transition and at free-standing shrubs in a coastal grassland in order to determine the effect of shrub encroachment on plant community and microclimate. Species richness was significantly lower inside shrub thickets. Soil water content, organic matter, nitrogen (N), carbon (C), and LAI were higher in shrub thickets and free-standing shrubs compared to grasslands. Summer and fall maximum temperatures were lower and more moderate where shrubs were present. Fall and winter minimum temperatures were highest inside shrub thickets. Native shrubs impact microclimate and species composition immediately upon encroachment. These shrubs lower overall species composition, increase soil nutrients and moisture, moderate summer temperature, and increase winter temperature, which has consequences on a larger scale. As barrier islands are critical for protecting marsh and mainland habitats, understanding this mechanism for shrub expansion is important to predict future encroachment of shrubs and displacement of grassland habitat
Close contact restriction periods for patients who received iodine-131 therapy for differentiated thyroid cancer
Objective. Patients treated with radionuclide therapy may require
restrictions on certain activities for a period of time following treatment to
optimise protection of the public and ensure the legal dose limit is not
exceeded. Software may be used to calculate necessary restriction periods for
an individual based on longitudinal dose rate measurements from the time of
radiopharmaceutical administration. A spreadsheet program has been used for
this purpose in Australian hospitals for the last two decades. However, this
spreadsheet has a limitation in that it uses an approximation in the
calculation of dose from a contact pattern, which affects the calculated
restriction period. A computer program called Dorn was developed that provides
the same functionality as the spreadsheet but without this approximation.
Proffered radiation safety advice from Dorn and the spreadsheet were compared.
Approach. Advice from the spreadsheet and Dorn were compared for 55 patients
who underwent iodine-131 therapy for differentiated thyroid cancer. Main
results. The restriction periods for caring for infants, close contact with
children and sleeping with a partner were typically about 13 hours longer in
Dorn than in the spreadsheet, but in some cases were over a week shorter or a
month longer. Significance. If the Dorn program is used clinically in place of
the spreadsheet, some patients will enjoy shorter restriction periods and the
therapy provider can be more confident in their compliance with regulatory
requirements and best practice. Dorn is freely available from
https://doi.org/jg5f.Comment: 17 pages, 16 figure
Loop amplitudes in gauge theories: modern analytic approaches
This article reviews on-shell methods for analytic computation of loop
amplitudes, emphasizing techniques based on unitarity cuts. Unitarity
techniques are formulated generally but have been especially useful for
calculating one-loop amplitudes in massless theories such as Yang-Mills theory,
QCD, and QED.Comment: 34 pages. Invited review for a special issue of Journal of Physics A
devoted to "Scattering Amplitudes in Gauge Theories." v2: typesetting macro
error fixe
A direct proof of the CSW rules
Using recursion methods similar to those of Britto, Cachazo, Feng and Witten
(BCFW) a direct proof of the CSW rules for computing tree-level gluon
amplitudes is given.Comment: 11 pages, uses axodraw.st
Multigluon tree amplitudes with a pair of massive fermions
We consider the calculation of n-point multigluon tree amplitudes with a pair
of massive fermions in QCD. We give the explicit transformation rules of this
kind of massive fermion-pair amplitudes with respect to different reference
momenta and check the correctness of them by SUSY Ward identities. Using these
rules and onshell BCFW recursion relation, we calculate the analytic results of
several n-point multigluon amplitudes.Comment: 15page
Antibacterial Fluoromicas: A Novel Delivery Medium
Antibacterial fluoromicas were prepared by ion-exchanging fluoromicas with different antibacterial agents including various quaternary ammonium compounds, AgNO3, and norfloxacin. Antibacterial activities of the ion-exchanged fluoromicas were determined against Staphylococcus aureus and Escherichia coli. Minimum inhibitory concentration (MIC) and zone of inhibition (ZOI) tests were performed to determine both antibacterial effectiveness and mode of action associated with the fluoromicas. All treated fluoromicas showed excellent antibacterial activities against both types of bacteria. The antibacterial activities of treated fluoromicas were found to be either better than or the same as those of neat antibacterial agents. The repeated antibacterial activity tests demonstrated the extended activity of these systems. © 2007 Elsevier B.V. All rights reserved
Adding flavour to twistor strings
Twistor string theory is known to describe a wide variety of field theories
at tree-level and has proved extremely useful in making substantial progress in
perturbative gauge theory. We explore the twistor dual description of a class
of N=2 UV-finite super-Yang-Mills theories with fundamental flavour by adding
'flavour' branes to the topological B-model on super-twistor space and comment
on the appearance of these objects. Evidence for the correspondence is provided
by matching amplitudes on both sides.Comment: 6 pages; contribution to the proceedings for the European Physical
Society conference on High Energy Physics in Manchester, 19-25 July 2007. v3:
Typos correcte
MHV Techniques for QED Processes
Significant progress has been made in the past year in developing new `MHV'
techniques for calculating multiparticle scattering amplitudes in Yang-Mills
gauge theories. Most of the work so far has focussed on applications to Quantum
Chromodynamics, both at tree and one-loop level. We show how such techniques
can also be applied to abelian theories such as QED, by studying the simplest
tree-level multiparticle process, e^+e^- to n \gamma. We compare explicit
results for up to n=5 photons using both the Cachazo, Svrcek and Witten `MHV
rules' and the related Britto-Cachazo-Feng `recursion relation' approaches with
those using traditional spinor techniques.Comment: 19 pages, 10 figures. References adde
Photon-Graviton Amplitudes from the Effective Action
We report on the status of an ongoing effort to calculate the complete
one-loop low-energy effective actions in Einstein-Maxwell theory with a massive
scalar or spinor loop, and to use them for obtaining the explicit form of the
corresponding M-graviton/N-photon amplitudes. We present explicit results for
the effective actions at the one-graviton four-photon level, and for the
amplitudes at the one-graviton two-photon level. As expected on general
grounds, these amplitudes relate in a simple way to the corresponding
four-photon amplitudes. We also derive the gravitational Ward identity for the
1PI one-graviton -- N photon amplitude.Comment: 9 pages, 2 figures, talk given by C. Schubert at "Supersymmetries and
Quantum Symmetries - SQS`2011", JINR Dubna, July 18 - 23, 2011 (to appear in
the Proceedings
- …