2,409 research outputs found
Hadronic event structure, power corrections and the strong coupling at LEP
Infrared and collinear events shapes are suited to directly probe properties
of hard QCD. They are traditionally used to measure the strong coupling and to
test the gauge structure of QCD. Perturbative predictions exist in several
variations all of which depend on the renormalisation scheme leading to large
theoretical uncertainties in the determination of . To overcome this
dominating error more and more schemes for setting the renormalisation scale
are investigated. The application of RGI perturbation theory shows an
incredible small spread of indicating a reduced uncertainty and
allows a measurement of the -function directly from mean values.Comment: 5 pages, uses moriond.sty (included). Contribution to "XXXVIIth
Rencontres de Moriond, QCD and hadronic interactions", Les Arcs, France,
March 2002. See http://www.delphi.uni-wuppertal.de/qcd/Talks.html#Moriond200
Scenario generation and scenario quality using the cone of plausibility
The intelligence analysis domain is a critical area for futures work. Indeed, intelligence analysts’ judgments of security threats are based on considerations of how futures may unfold, and as such play a vital role in informing policy- and decision-making. In this domain, futures are typically considered using qualitative scenario generation techniques such as the cone of plausibility (CoP). We empirically examined the quality of scenarios generated using this technique on five criteria: completeness, context (otherwise known as ‘relevance/pertinence’), plausibility, coherence, and order effects (i.e., ‘transparency’). Participants were trained to use the CoP and then asked to generate scenarios that might follow within six months of the Turkish government banning Syrian refugees from entering the country. On average, participants generated three scenarios, and these could be characterized as baseline, best case, and worst case. All scenarios were significantly more likely to be of high quality on the ‘coherence’ criterion compared to the other criteria. Scenario quality was independent of scenario type. However, scenarios generated first were significantly more likely to be of high quality on the context and order effects criteria compared to those generated afterwards. We discuss the implications of these findings for the use of the CoP as well as other qualitative scenario generation techniques in futures studies
Hadron masses and power corrections to event shapes
It is widely believed that hadronisation leads to 1/Q corrections to e+e- event shapes. We show that there are further corrections, proportional to (ln Q)^A/Q with A=4C_A/beta_0~=1.6, associated with hadron masses and whose relative normalisations can be calculated from one observable to another. At today's energies these extra corrections can be of the same order of magnitude as `traditional' 1/Q corrections. They fall into two classes: universal and non-universal. The latter can be eliminated by suitable redefinitions of the observables
Using scenarios to forecast outcomes of a refugee crisis
The Syrian civil war has led to millions of Syrians fleeing the country, and has resulted in a humanitarian crisis. By considering how such socio-political events may unfold, scenarios can lead to informed forecasts that can be used for decision-making. We examined the relationship between scenarios and forecasts in the context of the Syrian refugee crisis. Forty Turkish students trained to use a brainstorming technique generated scenarios that might follow within six months of the Turkish government banning Syrian refugees from entering the country. Participants generated from 3-6 scenarios. Over half were rated as ‘high’ quality in terms of completeness, relevance/pertinence, plausibility, coherence, and transparency (order effects). Scenario quality was unaffected by scenario quantity. Even though no forecasts were requested, participants’ first scenarios contained from 0-17 forecasts. Mean forecast accuracy was 45% and this was unaffected by forecast quantity. Therefore, brainstorming can offer a simple and quick way of generating scenarios and forecasts that can potentially help decision-makers tackle humanitarian crises
Tuning Monte Carlo Generators: The Perugia Tunes
We present 9 new tunes of the pT-ordered shower and underlying-event model in
PYTHIA 6.4. These "Perugia" tunes update and supersede the older "S0" family.
The data sets used to constrain the models include hadronic Z0 decays at LEP,
Tevatron minimum-bias data at 630, 1800, and 1960 GeV, Tevatron Drell-Yan data
at 1800 and 1960 GeV, and SPS min-bias data at 200, 546, and 900 GeV. In
addition to the central parameter set, called "Perugia 0", we introduce a set
of 8 related "Perugia Variations" that attempt to systematically explore soft,
hard, parton density, and colour structure variations in the theoretical
parameters. Based on these variations, a best-guess prediction of the charged
track multiplicity in inelastic, nondiffractive minimum-bias events at the LHC
is made. Note that these tunes can only be used with PYTHIA 6, not with PYTHIA
8. Note: this report was updated in March 2011 with a new set of variations,
collectively labeled "Perugia 2011", that are optimized for matching
applications and which also take into account some lessons from the early LHC
data. In order not to break the original text, these are described separately
in Appendix B. Note 2: a subsequent "Perugia 2012" update is described in
Appendix C.Comment: 46 page
Stability and electronic structure of the complex KPtCl structure-type hydrides
The stability and bonding of the ternary complex KPtCl structure
hydrides is discussed using first principles density functional calculations.
The cohesion is dominated by ionic contributions, but ligand field effects are
important, and are responsible for the 18-electron rule. Similarities to oxides
are discussed in terms of the electronic structure. However, phonon
calculations for SrRuH also show differences, particularly in the
polarizability of the RuH octahedra. Nevertheless, the yet to be made
compounds PbRuH and BeFeH are possible ferroelectrics. The
electronic structure and magnetic properties of the decomposition product,
FeBe are reported. Implications of the results for H storage are discussed
TensorFlow Estimators: Managing Simplicity vs. Flexibility in High-Level Machine Learning Frameworks
We present a framework for specifying, training, evaluating, and deploying
machine learning models. Our focus is on simplifying cutting edge machine
learning for practitioners in order to bring such technologies into production.
Recognizing the fast evolution of the field of deep learning, we make no
attempt to capture the design space of all possible model architectures in a
domain- specific language (DSL) or similar configuration language. We allow
users to write code to define their models, but provide abstractions that guide
develop- ers to write models in ways conducive to productionization. We also
provide a unifying Estimator interface, making it possible to write downstream
infrastructure (e.g. distributed training, hyperparameter tuning) independent
of the model implementation. We balance the competing demands for flexibility
and simplicity by offering APIs at different levels of abstraction, making
common model architectures available out of the box, while providing a library
of utilities designed to speed up experimentation with model architectures. To
make out of the box models flexible and usable across a wide range of problems,
these canned Estimators are parameterized not only over traditional
hyperparameters, but also using feature columns, a declarative specification
describing how to interpret input data. We discuss our experience in using this
framework in re- search and production environments, and show the impact on
code health, maintainability, and development speed.Comment: 8 pages, Appeared at KDD 2017, August 13--17, 2017, Halifax, NS,
Canad
- …