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101.
Svend Domdey Hans-Jürgen Pirner Urs Achim Wiedemann 《The European Physical Journal C - Particles and Fields》2010,65(1-2):153-162
The scale factor σ eff is the effective cross section used to characterize the measured rate of inclusive double dijet production in high-energy hadron collisions. It is sensitive to the two-parton distributions in the hadronic projectile. In principle, the scale factor depends on the center of mass energy and on the minimal transverse energy E T,min? of the jets contributing to the double dijet cross section. Here, we point out that proton–proton collisions at the LHC will provide for the first time experimental access to these scale dependences in a logarithmically wide, nominally perturbative kinematic range 10?E T,min??100 GeV. This constrains the dependence of two-parton distribution functions on parton momentum fractions and parton localization in impact parameter space. Novel information is to be expected about the transverse growth of hadronic distribution functions in the range of semi-hard Bjorken x (0.001?x?0.1) and high resolution Q 2. We discuss to what extent one can disentangle different pictures of the x-evolution of two-parton distributions in the transverse plane by measuring double-hard scattering events at the LHC. 相似文献
102.
Kazem Bitaghsir Fadafan Hong Liu Krishna Rajagopal Urs Achim Wiedemann 《The European Physical Journal C - Particles and Fields》2009,61(4):553-567
We determine the energy it takes to move a test quark along a circle of radius L with angular frequency ω through the strongly coupled plasma of
supersymmetric Yang–Mills (SYM) theory. We find that for most values of L and ω the energy deposited by stirring the plasma in this way is governed either by the drag force acting on a test quark moving
through the plasma in a straight line with speed v=L
ω or by the energy radiated by a quark in circular motion in the absence of any plasma, whichever is larger. There is a continuous
crossover from the drag-dominated regime (ω≲π
T(1−v
2)3/4, meaning ω≲π
T and L small enough) to the radiation-dominated regime (ω≳π
T(1−v
2)3/4). In the crossover regime we find evidence for significant destructive interference between energy loss due to drag and due
to radiation as if in vacuum. The rotating quark thus serves as a model system in which the relative strength of, and interplay
between, two different mechanisms of parton energy loss is accessible via a controlled classical gravity calculation. We close
by speculating on the implications of our results for a quark that is moving through the plasma in a straight line while decelerating,
although in this case the classical calculation breaks down at the same value of the deceleration as the one at which the
radiation-dominated regime sets in. 相似文献
103.
We show that for a certain family of initial data, there exist non-unique weak solutions to the 3D incompressible Euler equations satisfying the weak energy inequality, whereas the weak limit of every sequence of Leray–Hopf weak solutions for the Navier–Stokes equations, with the same initial data, and as the viscosity tends to zero, is uniquely determined and equals the shear flow solution of the Euler equations corresponding to this initial data. This simple example suggests that, also in more general situations, the vanishing viscosity limit of the Navier–Stokes equations could serve as a uniqueness criterion for weak solutions of the Euler equations. 相似文献
104.
105.
106.
Thermal analysis has been used to study the composition of paper and paper-like materials for some decades. The application
of these techniques permits to distinguish between the original paper which was used by the artists and possible forgeries.
Quite often, however, the identification of the differences demands the simultaneous application of several other techniques.
The present investigation includes Asiatic wood-prints from China and Japan, and lithographs of European artists, such as
Pablo Picasso, Salvador Dali, and Marc Chagall. Utamaro (1753–1806) is one of the most celebrated artists in the history of
the Japanese woodblock print. He became one of the famous painters of ‘Ukiyo-e’ (Ukiyo-e means transitory world). In China
Utamaro's pictures were also produced. The differences are found in the kind of paper: The Japanese used Mitsumata paper,
while the Chinese printed on Bamboo paper mixed with silk fibers. Hu-jü-zong (Nanking, 1619) and a group of famous Chinese
painters created the book of the ‘Ten Bamboo Studio’ which contains woodblock prints as visual aids for young artists. A reprint
of these woodblock prints appeared in 1717. Later, a bootleg of this book appeared in Japan (1817). The differentiation is
possible by thermogravimetric investigation of the used papers. Statistic evaluations in Europe show that more than 1 000
000 bootleg copies of lithographs of Pablo Picasso, Salvador Dali, and Marc Chagall exist. Thermoanalytical measurements allow
the distinction between the original artifacts and the bootlegs. Raman spectroscopy gives an additional possibility for the
distinction between the applied color pigments.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
107.
Ohne Zusammenfassung 相似文献
108.
Wiedemann SH Kang DH Bergman RG Friend CM 《Journal of the American Chemical Society》2007,129(15):4666-4677
Rearrangement reactions of C4-alkoxides on O-covered Mo(110) have been studied using temperature-programmed reaction spectroscopy and reflection-absorption infrared spectroscopy. Cyclobutoxide on Mo(110), prepared from the corresponding alcohol or bromide, is described for the first time in detail. Several reaction mechanisms are considered for the ring-opening rearrangement of cyclopropylmethoxide during high-temperature annealing. In light of compelling new data, previous results are reinterpreted to support the formation of transient cations near O-covered Mo(110). For the first time, we present strong evidence for clean, heterolytic bond cleavage reactions over a metal surface. Our revised reactivity model is based on spectroscopic and reactivity data that show the rearrangement of cyclopropylmethyl groups to cyclobutyl groups and vice versa. Selectively deuterated 1,1-D2-cyclopropylmethanol was studied as a test of mechanism and as a probe for the lifetime of reactive intermediates. Isotopic scrambling observed for this substrate is consistent with the formation of a relatively long-lived carbocation during rearrangement. The intermediacy of transient cations is further invoked to explain the rearrangements that are now recognized to occur as alkyl bromides are transformed into alkoxides on Mo(110)-(1 x 6)-O. The observed ring expansion/contraction reactions are characteristic of a cationic process; carbon-centered radicals are not known to rearrange in this manner. However, in none of the cases discussed could contributions from radical pathways be completely ruled out. Our results are compared to analogous reactions in the vapor and solution phases. General trends governing rearrangement mechanisms on Mo(110) are presented with respect to metal-surface coverage, heteroatom incorporation, and temperature. Trends are discussed in the context of heterogeneous hydrocarbon oxidation. 相似文献
109.
Dr.-Ing. M. Wiedemann Prof. Dr.-Ing. R. Gasch 《Archive of Applied Mechanics (Ingenieur Archiv)》1993,63(4-5):337-344
Übersicht In modernen Turbosätzen mit ihren langen Blättern im Niederdruckteil treten Fällen gekoppelter Strang-Torsionsschwingungen und Blatt-Biegeschwingungen auf mit Eigenfrequenzen in der Nähe der doppeltumlauffrequenten Erregung. Die Bestimmung der gekoppelten Rotor-Blatt-Schwingungen benötigt eine Berechnung des Gesamtsystems anstelle der traditionell getrennten Berechnung von Rotor und Blättern. Seit den 80er Jahren wurden eine Reihe von Vorschlägen gemacht, wie man die Berechnung des Gesamtsystems mit seiner enormen Anzahl von Freiheitsgraden vermeiden könne.In diesem Aufsatz wird eine systematische Methode vorgestellt, wie man-ausgehend von demFE-Gesamtsystem-zu Substrukturen für den Torsionsstrang (Rotor) und das Blatt gelangt und mit Hilfe ihrer Berechnung zu einer sehr starken Reduktion der Zahl der Freiheitsgrade für die notwendigen Untersuchungen des gekoppelten Systems. Nur wenige Transformationen und einfache Regeln für die Beschreibung der Kopplung führen zu einer Reduktion um mehr als 99 Prozent mit nahezu keinem Verlust an Ergebnisgenauigkeit.
Rotor-blade-coupling
Summary In large-capacity turbine generators with lognLP-blades torsional vibrations of the shaft or drive train and blade bending vibrations lead to coupled frequencies of the shaft-blade system often less or near the frequency twice the line frequency. The analysis of the haft-blade coupled vibrations needs a calculation for the whole system instead of the traditionally separated calculation of shaft and blade.Since the early 1980s several proposals were made to avoid the calculation of the whole system with its huge number of degress of freedom.Within this paper a systematical method will be presented how to derive substructures from the completeFE-model of the shaft-blade-system and how to achive a very strong reduction of the numbers of degrees of freedom for the equations of motion of the coupled system. Only a few transformations and simple rules for the coupling lead to more than 99 percent reduction in the number of dregrees of freedom with nearly no loss in acuracy.相似文献
110.