350 research outputs found
RESULTS OF A QUALITATIVE SURVEY ABOUT THE AP-PLICATION OF BUSINESS INFORMATION SYSTEMS IN GERMAN CRAFT ENTERPRISES - FIRST FINDINGS OF AN ONGOING RESEARCH PROJECT
The present study shows the current status of a preliminary study about the use of business infor-mation systems (BIS) based on five exemplarily selected case studies in German craft enterprises. The question of whether similarities and differences concerning the application of information and com-munication technologies (ICT) exist in practice. For this purpose, exemplary case demonstrating the scope and usage of organizational ICT in various crafts are presented. The case studies are based on a survey of CEOs and IT managers of selected craft enterprises. Based on the results of the survey, hypotheses about the use of information technologies were derived. Based on these hypotheses, inter-dependencies of craft enterprises are presented and justified regarding the use of BIS, the actuality of the hardware, the requirements to branch-specific IT solutions, the measures taken toward data pro-tection and data security and the visibility on the Internet. As a result of the preliminary study it can be stated that a widely heterogeneous IT landscape as well as good IT competence can be found in the enterprises involved
Observational Challenges for the Standard FLRW Model
We summarise some of the main observational challenges for the standard
Friedmann-Lemaitre-Robertson-Walker cosmological model and describe how results
recently presented in the parallel session `Large--scale Structure and
Statistics' (DE3) at the `Fourteenth Marcel Grossman Meeting on General
Relativity' are related to these challenges.Comment: 17 pages; references added. Matches published version in Int. J. Mod.
Phys. D; Report on Parallel Session DE3 of MG1
Critical Exponents of the Superconducting Phase Transition
We study the critical exponents of the superconducting phase transition in
the context of renormalization group theory starting from a dual formulation of
the Ginzburg-Landau theory. The dual formulation describes a loop gas of
Abrikosov flux tubes which proliferate when the critical temperature is
approached from below. In contrast to the Ginzburg-Landau theory, it has a
spontaneously broken global symmetry and possesses an infrared stable fixed
point. The exponents coincide with those of a superfluid with reversed
temperature axis.Comment: Postscript file. For related work see www adress
http://www.physik.fu-berlin.de/kleiner_re.html in our homepage
http://www.physik.fu-berlin.de/kleinert.htm
Dual description of the superconducting phase transition
The dual approach to the Ginzburg-Landau theory of a
Bardeen-Cooper-Schrieffer superconductor is reviewed. The dual theory describes
a grand canonical ensemble of fluctuating closed magnetic vortices, of
arbitrary length and shape, which interact with a massive vector field
representing the local magnetic induction. When the critical temperature is
approached from below, the magnetic vortices proliferate. This is signaled by
the disorder field, which describes the loop gas, developing a non-zero
expectation value in the normal conducting phase. It thereby breaks a {\it
global} U(1) symmetry. The ensuing Goldstone field is the magnetic scalar
potential. The superconducting-to-normal phase transition is studied by
applying renormalization group theory to the dual formulation. In the regime of
a second-order transition, the critical exponents are given by those of a
superfluid with a reversed temperature axis.Comment: Latex + Postscript file
Normative Intercorrelations Between EEG Microstate Characteristics.
EEG microstates are brief, recurring periods of stable brain activity that reflect the activation of large-scale neural networks. The temporal characteristics of these microstates, including their average duration, number of occurrences, and percentage contribution have been shown to serve as biomarkers of mental and neurological disorders. However, little is known about how microstate characteristics of prototypical network types relate to each other. Normative intercorrelations among these parameters are necessary to help researchers better understand the functions and interactions of underlying networks, interpret and relate results, and generate new hypotheses. Here, we present a systematic analysis of intercorrelations between EEG microstate characteristics in a large sample representative of western working populations (nâ=â583). Notably, we find that microstate duration is a general characteristic that varies across microstate types. Further, microstate A and B show mutual reinforcement, indicating a relationship between auditory and visual sensory processing at rest. Microstate C appears to play a special role, as it is associated with longer durations of all other microstate types and increased global field power, suggesting a relationship of these parameters with the anterior default mode network. All findings could be confirmed using independent EEG recordings from a retest-session (nâ=â542)
On convex lower-level black-box constraints in bilevel optimization with an application to gas market models with chance constraints
Bilevel optimization is an increasingly important tool to model hierarchical decision making. However, the ability of modeling such settings makes bilevel problems hard to solve in theory and practice. In this paper, we add on the general difficulty of this class of problems by further incorporating convex black-box constraints in the lower level. For this setup, we develop a cutting-plane algorithm that computes approximate bilevel-feasible points. We apply this method to a bilevel model of the European gas market in which we use a joint chance constraint to model uncertain loads. Since the chance constraint is not available in closed form, this fits into the black-box setting studied before. For the applied model, we use further problem-specific insights to derive bounds on the objective value of the bilevel problem. By doing so, we are able to show that we solve the application problem to approximate global optimality. In our numerical case study we are thus able to evaluate the welfare sensitivity in dependence of the achieved safety level of uncertain load coverage
On the Reliability of the EEG Microstate Approach.
EEG microstates represent functional brain networks observable in resting EEG recordings that remain stable for 40-120ms before rapidly switching into another network. It is assumed that microstate characteristics (i.e., durations, occurrences, percentage coverage, and transitions) may serve as neural markers of mental and neurological disorders and psychosocial traits. However, robust data on their retest-reliability are needed to provide the basis for this assumption. Furthermore, researchers currently use different methodological approaches that need to be compared regarding their consistency and suitability to produce reliable results. Based on an extensive dataset largely representative of western societies (2 days with two resting EEG measures each; day one: nâ=â583; day two: nâ=â542) we found good to excellent short-term retest-reliability of microstate durations, occurrences, and coverages (average ICCsâ=â0.874-0.920). There was good overall long-term retest-reliability of these microstate characteristics (average ICCsâ=â0.671-0.852), even when the interval between measures was longer than half a year, supporting the longstanding notion that microstate durations, occurrences, and coverages represent stable neural traits. Findings were robust across different EEG systems (64 vs. 30 electrodes), recording lengths (3 vs. 2 min), and cognitive states (before vs. after experiment). However, we found poor retest-reliability of transitions. There was good to excellent consistency of microstate characteristics across clustering procedures (except for transitions), and both procedures produced reliable results. Grand-mean fitting yielded more reliable results compared to individual fitting. Overall, these findings provide robust evidence for the reliability of the microstate approach
A path integral approach to the dynamics of a random chain with rigid constraints
In this work the dynamics of a freely jointed random chain which fluctuates
at constant temperature in some viscous medium is studied. The chain is
regarded as a system of small particles which perform a brownian motion and are
subjected to rigid constraints which forbid the breaking of the chain. For
simplicity, all interactions among the particles have been switched off and the
number of dimensions has been limited to two. The problem of describing the
fluctuations of the chain in the limit in which it becomes a continuous system
is solved using a path integral approach, in which the constraints are imposed
with the insertion in the path integral of suitable Dirac delta functions. It
is shown that the probability distribution of the possible conformations in
which the fluctuating chain can be found during its evolution in time coincides
with the partition function of a field theory which is a generalization of the
nonlinear sigma model in two dimensions. Both the probability distribution and
the generating functional of the correlation functions of the positions of the
beads are computed explicitly in a semiclassical approximation for a
ring-shaped chain.Comment: 36 pages, 2 figures, LaTeX + REVTeX4 + graphicx, minor changes in the
text, reference adde
- âŠ