7,757 research outputs found
Configurable Process Models as a Basis for Reference Modeling
Off-the-shelf packages such as SAP need to be configured to suit the requirements of an organization. Reference models support the configuration of these systems. Existing reference models use rather traditional languages. For example, the SAP reference model uses Eventdriven Process Chains (EPCs). Unfortunately, traditional languages like EPCs do not capture the configuration-aspects well. Consider for example the concept of "choice" in the control-flow perspective. Although any process modeling language, including EPCs, offers a choice construct (e.g., the XOR connector in EPCs), a single construct will not be able to capture the time dimension, scope, and impact of a decision. Some decisions are taken at run-time for a single case while other decisions are taken at build-time impacting a whole organization and all current and future cases. This position paper discusses the need for configurable process models as a basic building block for reference modeling. The focus is on the control-flow perspective. Š Springer-Verlag Berlin Heidelberg 2006
Robust Flows over Time: Models and Complexity Results
We study dynamic network flows with uncertain input data under a robust
optimization perspective. In the dynamic maximum flow problem, the goal is to
maximize the flow reaching the sink within a given time horizon , while flow
requires a certain travel time to traverse an edge.
In our setting, we account for uncertain travel times of flow. We investigate
maximum flows over time under the assumption that at most travel times
may be prolonged simultaneously due to delay. We develop and study a
mathematical model for this problem. As the dynamic robust flow problem
generalizes the static version, it is NP-hard to compute an optimal flow.
However, our dynamic version is considerably more complex than the static
version. We show that it is NP-hard to verify feasibility of a given candidate
solution. Furthermore, we investigate temporally repeated flows and show that
in contrast to the non-robust case (that is, without uncertainties) they no
longer provide optimal solutions for the robust problem, but rather yield a
worst case optimality gap of at least . We finally show that the optimality
gap is at most , where and are newly introduced
instance characteristics and provide a matching lower bound instance with
optimality gap and . The results obtained in
this paper yield a first step towards understanding robust dynamic flow
problems with uncertain travel times
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The new BELUGA setup for collocated turbulence and radiation measurements using a tethered balloon: First applications in the cloudy Arctic boundary layer
The new BELUGA (Balloon-bornE moduLar Utility for profilinG the lower Atmosphere) tethered balloon system is introduced. It combines a set of instruments to measure turbulent and radiative parameters and energy fluxes. BELUGA enables collocated measurements either at a constant altitude or as vertical profiles up to 1.5km in height. In particular, the instrument payload of BELUGA comprises three modular instrument packages for high-resolution meteorological, wind vector and broadband radiation measurements. Collocated data acquisition allows for estimates of the driving parameters in the energy balance at various heights. Heating rates and net irradiances can be related to turbulent fluxes and local turbulence parameters such as dissipation rates. In this paper the technical setup, the instrument performance, and the measurement strategy of BELUGA are explained. Furthermore, the high vertical resolution due to the slow ascent speed is highlighted as a major advantage of tethered balloon-borne observations. Three illustrative case studies of the first application of BELUGA in the Arctic atmospheric boundary layer are presented. As a first example, measurements of a single-layer stratocumulus are discussed. They show a pronounced cloud top radiative cooling of up to 6K h-1. To put this into context, a second case elaborates respective measurements with BELUGA in a cloudless situation. In a third example, a multilayer stratocumulus was probed, revealing reduced turbulence and negligible cloud top radiative cooling for the lower cloud layer. In all three cases the net radiative fluxes are much higher than turbulent fluxes. Altogether, BELUGA has proven its robust performance in cloudy conditions of the Arctic atmospheric boundary layer
Beam Test of BTeV Pixel Detectors
The silicon pixel vertex detector is one of the key elements of the BTeV
spectrometer. Detector prototypes were tested in a beam at Fermilab. We report
here on the measured spatial resolution as a function of the incident angles
for different sensor-readout electronics combinations. We compare the results
with predictions from our Monte Carlo simulation.Comment: 7 pages, 5 figures, Invited talk given by J.C. Wang at "Vertex 2000,
9th International Workshop on Vertex Detectors", Michigan, Sept 10-15, 2000.
To be published in NIM
On Hausdorff dimension of the set of closed orbits for a cylindrical transformation
We deal with Besicovitch's problem of existence of discrete orbits for
transitive cylindrical transformations
where is an
irrational rotation on the circle \T and \varphi:\T\to\R is continuous,
i.e.\ we try to estimate how big can be the set
D(\alpha,\varphi):=\{x\in\T:|\varphi^{(n)}(x)|\to+\infty\text{as}|n|\to+\infty\}.
We show that for almost every there exists such that the
Hausdorff dimension of is at least . We also provide a
Diophantine condition on that guarantees the existence of
such that the dimension of is positive. Finally, for some
multidimensional rotations on \T^d, , we construct smooth
so that the Hausdorff dimension of is positive.Comment: 32 pages, 1 figur
Automatic Generation of Questionnaires for Supporting Users during the Execution of Declarative Business Process Models
When designing an imperative business process (BP) model,
analysts have to face many design requirements (e.g., managing uncertainty,
optimizing conflicting objective functions). To facilitate such
design, declarative BP models are increasingly used. However, how to
execute a given declarative model can be quite challenging since there are
typically several variants related to such model, each one presenting
different degree of goodness. To support users working on declarative
models while a high flexibility is maintained, we propose removing the
worst variants from the source declarative model at design time while
keeping the best variants. This way, the variants which are kept are narrowed
down incrementally during run-time. For managing these variants
during run-time we suggest to build upon configurable BP models. To
configure such models, we additionally propose to automatically generate
questionnaires. The results over a real case study are promising
Territorial Tactics: The Socio-spatial Significance of Private Policing Strategies in Cape Town
This paper analyses the policing strategies of private security companies operating in urban space. An existing literature has considered the variety of ways that territory becomes of fundamental importance in the work of public police forces. However, this paper examines territory in the context of private security companies. Drawing on empirical research in Cape Town, it examines how demarcated territories become key subjects in private policing. Private security companies are responsible for a relatively small section of the city, while in contrast the public police ultimately have to see city space as a whole. Hence, private policing strategy becomes one of displacement, especially of so-called undesirables yielding a patchworked public space associated with private enclaves of consumption. The conclusions signal the historical resonances and comparative implications of these political-legal-security dynamics. Š 2013 Urban Studies Journal Limited
Stratified spatiotemporal chaos in anisotropic reaction-diffusion systems
Numerical simulations of two dimensional pattern formation in an anisotropic
bistable reaction-diffusion medium reveal a new dynamical state, stratified
spatiotemporal chaos, characterized by strong correlations along one of the
principal axes. Equations that describe the dependence of front motion on the
angle illustrate the mechanism leading to stratified chaos
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