317 research outputs found
Top pair threshold production at a linear collider with WHIZARD
We briefly describe how the Monte Carlo generator WHIZARD 2.2 can be employed
to study large QCD effects enhancing the top-antitop production threshold at a
next-generation lepton collider. While present state-of-the-art predictions at
NNLL order are confined to inclusive total cross sections, our tool can be used
to simulate differential distributions including NLL threshold resummation in
the production, and with off-shell decaying tops. The new model will be shipped
with WHIZARD from version 2.2.3 onwards, to be released along with this
article.Comment: 4 pages, 1 figure. Proceedings of TOP2014, 7th International Workshop
on Top Quark Physics, Cannes, France, September 29 - October 3 201
On the Consistency of Ordinal Regression Methods
Many of the ordinal regression models that have been proposed in the
literature can be seen as methods that minimize a convex surrogate of the
zero-one, absolute, or squared loss functions. A key property that allows to
study the statistical implications of such approximations is that of Fisher
consistency. Fisher consistency is a desirable property for surrogate loss
functions and implies that in the population setting, i.e., if the probability
distribution that generates the data were available, then optimization of the
surrogate would yield the best possible model. In this paper we will
characterize the Fisher consistency of a rich family of surrogate loss
functions used in the context of ordinal regression, including support vector
ordinal regression, ORBoosting and least absolute deviation. We will see that,
for a family of surrogate loss functions that subsumes support vector ordinal
regression and ORBoosting, consistency can be fully characterized by the
derivative of a real-valued function at zero, as happens for convex
margin-based surrogates in binary classification. We also derive excess risk
bounds for a surrogate of the absolute error that generalize existing risk
bounds for binary classification. Finally, our analysis suggests a novel
surrogate of the squared error loss. We compare this novel surrogate with
competing approaches on 9 different datasets. Our method shows to be highly
competitive in practice, outperforming the least squares loss on 7 out of 9
datasets.Comment: Journal of Machine Learning Research 18 (2017
Anomalous top charged-current contact interactions in single top production at the LHC
In an effective theory approach, the full minimal set of leading
contributions to anomalous charged-current top couplings comprises various new
trilinear tbW as well as quartic tbff' interaction vertices, some of which are
related to one another by equations of motion. While much effort in earlier
work has gone into the extraction of the trilinear couplings from single top
measurements, we argue in this article that these structures can be assessed
independently by other observables, while single top production forms a unique
window to the four-fermion sector. An effective theory approach is employed to
infer and classify the minimal set of such couplings from dimension six
operators in the minimal flavor violation scheme. In the phenomenological
analysis, we present a Monte Carlo study at detector level to quantify the
expected performance of the next LHC run to bound as well as distinguish the
various contact couplings. Special attention is directed toward differential
final state distributions including detector effects as a means to optimize the
signal sensitivity as well as the discriminative power with respect to the
possible coupling structures.Comment: 33 pages, 10 figures. Published versio
Triplet Energy Transfer from Ruthenium Complexes to Chiral Eniminium Ions: Enantioselective Synthesis of Cyclobutanecarbaldehydes by [2+2] Photocycloaddition
Chiral eniminium salts, prepared from alpha,beta-unsaturated aldehydes and a chiral proline derived secondary amine, underwent, upon irradiation with visible light, a ruthenium-catalyzed (2.5 mol %) intermolecular [2+2] photocycloaddition to olefins, which after hydrolysis led to chiral cyclobutanecarbaldehydes (17 examples, 49-74 % yield), with high diastereo- and enantioselectivities. Ru(bpz)(3)(PF6)(2) was utilized as the ruthenium catalyst and laser flash photolysis studies show that the catalyst operates exclusively by triplet-energy transfer (sensitization). A catalytic system was devised with a chiral secondary amine co-catalyst. In the catalytic reactions, Ru(bpy)(3)(PF6)(2) was employed, and laser flash photolysis experiments suggest it undergoes both electron and energy transfer. However, experimental evidence supports the hypothesis that energy transfer is the only productive quenching mechanism. Control experiments using Ir(ppy)(3) showed no catalysis for the intermolecular [2+2] photocycloaddition of an eniminium ion
Influence of lipid profile and statin administration on arterial stiffness in renal transplant recipients
Background: Hyperlipidemia is one of the major risk factors for developing a cardiovascular disease (CVD) and it is a frequent post-transplant complication, occurring in up to 60% of the renal transplant recipients (RTRs). Lipid lowering therapy with HMG-CoA reductase inhibitors (statins) is generally recommended and may reduce the overall cardiovascular risk. The aim of this study was to evaluate the lipid profile, statin administration and their relationship with arterial stiffness parameters in renal transplant recipients.
Methods: Three hundred and forty-four stable RTRs (62.5% male) transplanted between 1994 and 2018 were randomly enrolled to the study. The following parameters of arterial stiffness was measured in each patient: carotid femoral pulse wave velocity (baPWV left and right, cfPWV) and pulse pressure (PP right and left). The study group was divided based on the use statins: 143 (41.6%) and 201 (58.4%). RTRs were qualified to the statin (+) and the statin (–) group, respectively.
Results: In the statin (+) as compared to statin (–) group there were more patients with a CVD (32.9% vs. 14.9%) and diabetes (25.2% vs. 14.4%). In the whole study group, CVD was associated with a significant increase of both baPWV and cfPWV as well as PP (8.5 mmHg). There were significant differences in arterial stiffness parameters (baPWV, cfPWV, PP) between the statin (+) and the statin (–) group.
Conclusions: Arterial stiffness was increased in RTRs with CVD and hyperlipidemia. The control of hyperlipidemia was poor in RTRs
Exclusive top production at a Linear Collider at and off the threshold
We review exclusive top pair production including decays at a future
high-energy lepton collider, both in the threshold region and for higher
energies. For the continuum process, we take complete QCD next-to-leading order
matrix elements for the process with leptonic W decays into account.
At threshold, we match the fixed-order relativistic QCD-NLO cross section to a
nonrelativistic cross section with next-to-leading logarithmic (NLL) threshold
resummation implemented via a form factor.Comment: Talk presented at the International Workshop on Future Linear
Colliders (LCWS2017), Strasbourg, France, 23-27 October 2017. C17-10-23.
A Guide for Publishing, Using, and Licensing Research Software in Germany
Research software has become a central asset in academic research. In Germany, the German Research Foundation (DFG, Deutsche Forschungsgemeinschaft) recently updated the Guidelines for Safeguarding Good Research Practice. Research software is now valued similarly to classic publications and data with implications for research software sustainability and legal aspects. In this document, we present four decision trees and corresponding legal documentation tables to aid researchers. The decision trees should ease to identify i) the software policy of your institution, ii) restrictions imposed by contributors and the environment, iii) licensing collisions if 3rd party software is included, and iv) problems in licensing (existing) research software
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Concentrations and Uptake of Dissolved Organic Phosphorus Compounds in the Baltic Sea
The dissolved organic phosphorus (DOP) pool in marine waters contains a variety of different compounds. Knowledge of the distribution and utilization of DOP by phyto- and bacterioplankton is limited, but critical to our understanding of the marine phosphorus cycle. In the Baltic Sea, detailed information about the composition of DOP and its turnover is lacking. This study reports the concentrations and uptake rates of DOP compounds, namely, adenosine triphosphate (dATP), deoxyribonucleic acid (dDNA), and phospholipids (dPL), in the Baltic Proper and in Finnish coastal waters in the summers of 2011 and 2012. Both areas differed in their dissolved inorganic phosphorus (DIP) concentrations (0.16 and 0.02–0.04 μM), in the C:P (123–178) and N:P (18–27) ratios, and in abundances of filamentous cyanobacteria and of autotrophic and heterotrophic picoplankton. The mean concentrations of dATP-P, dDNA-P, and dPL-P were 4.3–6.4, 0.05–0.12, and 1.9–6.8 nM, respectively, together contributing between 2.4 and 5.2% of the total DOP concentration. The concentrations of the compounds varied between and within the investigated regions and the distribution patterns of the individual components are not linked to each other. DIP was taken up at rates of 10.1–380.8 nM d-1. dATP-P and dDNA-P were consumed simultaneously with DIP at rates of 6.9–24.1 and 0.09–0.19 nM d-1, respectively, with the main proportion taken up by the size fraction <3 μm and with DIP to be the dominant source. Groups of hydrographical and biological parameters were identified in the multiple regression analysis to impact the concentrations and uptake rates. It points to the complexity of the regulation. Our results indicate that the investigated DOP compounds, particularly dATP-P, can make significant contributions to the P nutrition of microorganisms and their use seems to be not intertwined. Therefore, more detailed knowledge of all DOP components including variation of concentrations and the utilization is required to understand the roles of DOP in marine ecosystems
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