223 research outputs found
Effects of the Running of the QCD Coupling on the Energy Loss in the Quark-Gluon Plasma
Finite temperature modifies the running of the QCD coupling alpha_s(k,T) with
resolution k. After calculating the thermal quark and gluon masses
selfconsistently, we determine the quark-quark and quark-gluon cross sections
in the plasma based on the running coupling. We find that the running coupling
enhances these cross sections by factors of two to four depending on the
temperature. We also compute the energy loss dE/dx of a high-energy quark in
the plasma as a function of temperature. Our study suggests that, beside
t-channel processes, inverse Compton scattering is a relevant process for a
quantitative understanding of the energy loss of an incident quark in a hot
plasma.Comment: 14 pages, 6 figure
Condition monitoring of machines by tapping data from existing sensors and retrofitting simple energy measurement technology to existing machines
The average metal and mechanical engineering company must spend around two per cent of its annual turnover on electricity and natural gas, and companies are expecting
further price increases. As a result, the issue of energy saving is becoming more of a strategic factor than ever before. In order to save costs and ensure competitive
advantages, it is necessary to introduce precise energy-saving measures. The first steps taken by most mechanical engineering companies are to replace lighting, heating, and ventilation systems, improve compressed air generation and raise employee awareness. However, there is also a great potential for optimization in machines with their individual electrical drives, fans, and units. In this case, though, it is necessary to look at the machine and its processes as a whole rather than the individual electrical energy consumers. In most cases, however, there is a lack of suitable interfaces for analyzing the measured values from sensors (e.g. temperature, pressure sensors, etc.) and drives, which concludes that this potential is not fully exploited
Guest Editorial Preface: Special Issue on IT-Support for Crisis and Continuity Management
On 21 January 2013, there was a fire at the central office of a telecommunications network operator
in Siegen, which resulted in more than 500,000 telephone connections being collapsed for several
hours and occasionally several days. Emergency calls were also not possible. The websites of the
district and the control center were offline. The local radio which typically acts as a central point of
information in such situations was out of service. But not only the civic-societal continuity, also the
operational continuity was affected (Reuter et al., 2017). In this example, both continuity and crisis
management are essential to recover to regular business resp. life
Self-limited oxide formation in Ni(111) oxidation
The oxidation of the Ni(111) surface is studied experimentally with low
energy electron microscopy and theoretically by calculating the electron
reflectivity for realistic models of the NiO/Ni(111) surface with an ab-initio
scattering theory. Oxygen exposure at 300 K under ultrahigh-vacuum conditions
leads to the formation of a continuous NiO(111)-like film consisting of
nanosized domains. At 750 K, we observe the formation of a nano-heterogeneous
film composed primarily of NiO(111)-like surface oxide nuclei, which exhibit
virtually the same energy-dependent reflectivity as in the case of 300 K and
which are separated by oxygen-free Ni(111) terraces. The scattering theory
explains the observed normal incidence reflectivity R(E) of both the clean and
the oxidized Ni(111) surface. At low energies R(E) of the oxidized surface is
determined by a forbidden gap in the k_parallel=0 projected energy spectrum of
the bulk NiO crystal. However, for both low and high temperature oxidation a
rapid decrease of the reflectivity in approaching zero kinetic energy is
experimentally observed. This feature is shown to characterize the thickness of
the oxide layer, suggesting an average oxide thickness of two NiO layers.Comment: 10 pages (in journal format), 9 figure
ZustandsĂĽberwachung von Maschinen durch Datenabgriff an bestehender Sensorik und NachrĂĽstung einfacher Energiemesstechnik an Bestandsmaschinen
Metall- und Maschinenbauunternehmen mĂĽssen im Durchschnitt pro Jahr ca. zwei Prozent ihres Umsatzes fĂĽr Strom und Erdgas ausgeben und die Unternehmer gehen
von weiteren Preissteigerungen aus. Damit rückt das Thema Energieeinsparung stärker denn je in den Fokus und wird zu einem strategischen Faktor. Um Kosten zu sparen und Wettbewerbsvorteile zu sichern, ist es notwendig, zielgenaue Energieeinsparmaßnahmen einzuleiten. Die ersten Maßnahmen, welche die meisten Maschinenbauunternehmen umsetzen, sind die Erneuerung der Beleuchtungs-, Heizungs- und Lüftungsanlage, die Verbesserung der Drucklufterzeugung sowie die thematische Sensibilisierung der Mitarbeiter. Aber auch in Maschinen mit ihren dazugehörigen elektrischen Antrieben, Lüftern und Aggregaten verbirgt sich eine große Menge an Optimierungspotenzial. Allerdings ist es hier notwendig nicht die Verbraucher im Einzelnen, sondern die Maschine und deren Prozesse im Ganzen zu betrachten. Meist fehlen hierfür aber geeignete Schnittstellen, um die Messwerte von Sensoren (bspw. Temperatur-, Drucksensoren, etc.) und Antrieben auslesen zu können, was dazu führt, dass diese Potenziale nicht ausgeschöpft werden
Running coupling at finite temperature and chiral symmetry restoration in QCD
We analyze the running gauge coupling at finite temperature for QCD, using
the functional renormalization group. The running of the coupling is calculated
for all scales and temperatures. At finite temperature, the coupling is
governed by a fixed point of the 3-dimensional theory for scales smaller than
the corresponding temperature. The running coupling can drive the quark sector
to criticality, resulting in chiral symmetry breaking. Our results provide for
a quantitative determination of the phase boundary in the plane of temperature
and number of massless flavors. Using the experimental value of the coupling at
the tau mass scale as the only input parameter, we obtain, e.g., for N_f=3
massless flavors a critical temperature of T_cr ~ 148 MeV in good agreement
with lattice simulations.Comment: 6 pages, 3 figures; references added, results updated and discussion
expanded (matches PLB version
Parallel kinetic Monte Carlo simulation framework incorporating accurate models of adsorbate lateral interactions
Ab initio kinetic Monte Carlo (KMC) simulations have been successfully applied for over two decades to elucidate the underlying physico-chemical phenomena on the surfaces of heterogeneous catalysts. These simulations necessitate detailed knowledge of the kinetics of elementary reactions constituting the reaction mechanism, and the energetics of the species participating in the chemistry. The information about the energetics is encoded in the formation energies of gas and surface-bound species, and the lateral interactions between adsorbates on the catalytic surface, which can be modeled at different levels of detail. The majority of previous works accounted for only pairwise-additive first nearest-neighbor interactions. More recently, cluster-expansion Hamiltonians incorporating long-range interactions and many-body terms have been used for detailed estimations of catalytic rate [C. Wu, D. J. Schmidt, C. Wolverton, and W. F. Schneider, J. Catal. 286, 88 (2012)]. In view of the increasing interest in accurate predictions of catalytic performance, there is a need for general-purpose KMC approaches incorporating detailed cluster expansion models for the adlayer energetics. We have addressed this need by building on the previously introduced graph-theoretical KMC framework, and we have developed Zacros, a FORTRAN2003 KMC package for simulating catalytic chemistries. To tackle the high computational cost in the presence of long-range interactions we introduce parallelization with OpenMP. We further benchmark our framework by simulating a KMC analogue of the NO oxidation system established by Schneider and co-workers [J. Catal. 286, 88 (2012)]. We show that taking into account only first nearest-neighbor interactions may lead to large errors in the prediction of the catalytic rate, whereas for accurate estimates thereof, one needs to include long-range terms in the cluster expansion
7. Workshop Mensch-Maschine-Interaktion in sicherheitskritischen Systemen
Im Zentrum dieses Workshops steht die Interaktion von Mensch
und Technik in sicherheitskritischen Kontexten. Hierzu zählen
Anwendungsfelder, die bereits seit vielen Jahren Gegenstand der
Forschung und Entwicklung sind. Beispiele sind Katastrophenschutz oder Medizin, aber auch kritische Infrastrukturen. In
diesen und vielen weiteren Bereichen gilt, dass sicherere
Systemzustände nur durch die ganzheitliche Betrachtung von
Mensch, Technik und Organisation gewährleistet bzw.
schnellstmöglich wieder erreicht werden können. In diesem
Zusammenhang ist der Workshop auch der Nutzbarkeit und
Akzeptanz von Sicherheitskonzepten sowie einer bewussteren
Auseinandersetzung der Nutzenden mit diesen Themen
gewidmet
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