677 research outputs found
Towards the Amplituhedron Volume
21 pages; v2: version published in JHEPIt has been recently conjectured that scattering amplitudes in planar N=4 super Yang-Mills are given by the volume of the (dual) amplituhedron. In this paper we show some interesting connections between the tree-level amplituhedron and a special class of differential equations. In particular we demonstrate how the amplituhedron volume for NMHV amplitudes is determined by these differential equations. The new formulation allows for a straightforward geometric description, without any reference to triangulations. Finally we discuss possible implications for volumes related to generic N^kMHV amplitudes.Peer reviewe
Whole genome methylation profiles as independent markers of survival in stage IIIc melanoma patients
Background: The clinical course of cutaneous melanoma (CM) can differ significantly for patients with identical stages of disease, defined clinico-pathologically, and no molecular markers differentiate patients with such a diverse prognosis. This study aimed to define the prognostic value of whole genome DNA methylation profiles in stage III CM.Methods: Genome-wide methylation profiles were evaluated by the Illumina Human Methylation 27 BeadChip assay in short-term neoplastic cell cultures from 45 stage IIIC CM patients. Unsupervised K-means partitioning clustering was exploited to sort patients into 2 groups based on their methylation profiles. Methylation patterns related to the discovered groups were determined using the nearest shrunken centroid classification algorithm. The impact of genome-wide methylation patterns on overall survival (OS) was assessed using Cox regression and Kaplan-Meier analyses.Results: Unsupervised K-means partitioning by whole genome methylation profiles identified classes with significantly different OS in stage IIIC CM patients. Patients with a " favorable" methylation profile had increased OS (P = 0.001, log-rank = 10.2) by Kaplan-Meier analysis. Median OS of stage IIIC patients with a " favorable" vs. " unfavorable" methylation profile were 31.5 and 10.4 months, respectively. The 5 year OS for stage IIIC patients with a " favorable" methylation profile was 41.2% as compared to 0% for patients with an " unfavorable" methylation profile. Among the variables examined by multivariate Cox regression analysis, classification defined by methylation profile was the only predictor of OS (Hazard Ratio = 2.41, for " unfavorable" methylation profile; 95% Confidence Interval: 1.02-5.70; P = 0.045). A 17 gene methylation signature able to correctly assign prognosis (overall error rate = 0) in stage IIIC patients on the basis of distinct methylation-defined groups was also identified.Conclusions: A discrete whole-genome methylation signature has been identified as molecular marker of prognosis for stage IIIC CM patients. Its use in daily practice is foreseeable, and promises to refine the comprehensive clinical management of stage III CM patients. Š 2012 Sigalotti et al.; licensee BioMed Central Ltd
rEHR: An R package for manipulating and analysing Electronic Health Record data
Research with structured Electronic Health Records (EHRs) is expanding as data becomes more accessible; analytic methods advance; and the scientific validity of such studies is increasingly accepted. However, data science methodology to enable the rapid searching/extraction, cleaning and analysis of these large, often complex, datasets is less well developed. In addition, commonly used software is inadequate, resulting in bottlenecks in research workflows and in obstacles to increased transparency and reproducibility of the research. Preparing a research-ready dataset from EHRs is a complex and time consuming task requiring substantial data science skills, even for simple designs. In addition, certain aspects of the workflow are computationally intensive, for example extraction of longitudinal data and matching controls to a large cohort, which may take days or even weeks to run using standard software. The rEHR package simplifies and accelerates the process of extracting ready-for-analysis datasets from EHR databases. It has a simple import function to a database backend that greatly accelerates data access times. A set of generic query functions allow users to extract data efficiently without needing detailed knowledge of SQL queries. Longitudinal data extractions can also be made in a single command, making use of parallel processing. The package also contains functions for cutting data by time-varying covariates, matching controls to cases, unit conversion and construction of clinical code lists. There are also functions to synthesise dummy EHR. The package has been tested with one for the largest primary care EHRs, the Clinical Practice Research Datalink (CPRD), but allows for a common interface to other EHRs. This simplified and accelerated work flow for EHR data extraction results in simpler, cleaner scripts that are more easily debugged, shared and reproduced
Wilson Loop Renormalization Group Flows
The locally BPS Wilson loop and the pure gauge Wilson loop map under AdS/CFT
duality to string world-sheet boundaries with standard and alternate
quantizations of the world-sheet fields. This implies an RG flow between the
two operators, which we verify at weak coupling. Many additional loop operators
exist at strong coupling, with a rich pattern of RG flows.Comment: 10 p, 2 figures. v3: Title change, expanded treatment of RG flow
Resummation of transverse energy in vector boson and Higgs boson production at hadron colliders
We compute the resummed hadronic transverse energy (E_T) distribution due to
initial-state QCD radiation in vector boson and Higgs boson production at
hadron colliders. The resummed exponent, parton distributions and coefficient
functions are treated consistently to next-to-leading order. The results are
matched to fixed-order calculations at large E_T and compared with
parton-shower Monte Carlo predictions at Tevatron and LHC energies.Comment: 24 pages, 15 figure
First-principles derivation of the AdS/CFT Y-systems
We provide a first-principles, perturbative derivation of the AdS5/CFT4
Y-system that has been proposed to solve the spectrum problem of N=4 SYM. The
proof relies on the computation of quantum effects in the fusion of some loop
operators, namely the transfer matrices. More precisely we show that the
leading quantum corrections in the fusion of transfer matrices induce the
correct shifts of the spectral parameter in the T-system. As intermediate steps
we study UV divergences in line operators up to first order and compute the
fusion of line operators up to second order for the pure spinor string in
AdS5xS5. We also argue that the derivation can be easily extended to other
integrable models, some of which describe string theory on AdS4, AdS3 and AdS2
spacetimes.Comment: 45 pages, 5 figures; v2: minor additions, JHEP versio
Probing the low transverse momentum domain of Z production with novel variables
The measurement of the low transverse momentum region of vector boson
production in Drell-Yan processes has long been invaluable to testing our
knowledge of QCD dynamics both beyond fixed-order in perturbation theory as
well as in the non-perturbative region. Recently the D\O\ collaboration have
introduced novel variables which lead to improved measurements compared to the
case of the standard QT variable. To complement this improvement on the
experimental side, we develop here a complete phenomenological study dedicated
in particular to the new \phi* variable. We compare our study, which contains
the state-of-the-art next-to-next-to-leading resummation of large logarithms
and a smooth matching to the full next-to-leading order result, to the
experimental data and find excellent agreement over essentially the entire
range of \phi*, even without direct inclusion of non-perturbative effects. We
comment on our findings and on the potential for future studies to constrain
non-perturbative behaviour.Comment: 20 pages, 7 figures. Version accepted for publication in JHEP. A
figure with comparison to RESBOS has been adde
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