1,769 research outputs found
Main-Group Metallocenophanes
Metallocenes with interlinked cyclopentadienide ligands are commonly referred to as ansaâmetallocenes or metallocenophanes. These can have drastically different properties than their unbridged parent compounds. While this concept is best known for transition metals such as iron, it can also be adopted for many mainâgroup elements. This review aims to summarize recent advances in the field of metallocenophanes based on mainâgroup elements of group 2, group 13, group 14 and group 15, focusing on synthesis, structure and properties of these compounds
Pentaisopropyl Cyclopentadienyl: An Overview across the Periodic Table
Cyclopentadienide (Cp) groups are among the most popular ligands in organometallic chemistry. Sterically demanding substitution patterns on the Cp ring can have an important effect on the ligand properties and there are many examples of metal complex which are only stable and isolatable with sterically demanding Cp ligands, carrying alkyl or aryl groups. Among these sterically demanding Cp ligands, pentaisopropylcyclopentadienide is the bulkiest pentaalkyl derivative and has been utilized in main group, as well as transition metal and rare-earth element chemistry for several decades
Direct determinations of the nucleon and pion terms at nearly physical quark masses
We present a high statistics study of the pion and nucleon light and strange
quark sigma terms using dynamical non-perturbatively improved clover
fermions with a range of pion masses down to MeV and several
volumes, up to , and lattice spacings, fm,
enabling a study of finite volume and discretisation effects for MeV. Systematics are found to be reasonably under control. For the nucleon
we obtain MeV and MeV, or equivalently
in terms of the quark fractions, , and
, where the errors include estimates of both the systematic
and statistical uncertainties. These values, together with perturbative
matching in the heavy quark limit, lead to ,
and . In addition, through the use of the
(inverse) Feynman-Hellmann theorem our results for are shown
to be consistent with the nucleon masses determined in the analysis. For the
pion we implement a method which greatly reduces excited state contamination to
the scalar matrix elements from states travelling across the temporal boundary.
This enables us to demonstrate the Gell-Mann-Oakes-Renner expectation
over our range of pion masses.Comment: 31 pages, 18 figures, v2, small changes to text and figure
Heavier N-heterocyclic half-sandwich tetrylenes
ansa-Half-sandwich complexes of the group 14 elements germanium, tin and lead are reported, which represent a new class of Lewis amphiphilic tetrylenes and bridge the gap between classical N-heterocyclic systems and group 14 metallocenes. These compounds can form complexes both with carbenes and transition metal fragments
Codeklonerkennung mit Dominatorinformationen
If an existing function in a software project is copied and reused (in a slightly modiïŹed version), the result is a code clone. If there was an error or vulnerability in the original function, this error or vulnerability is now contained in several places in the software project. This is one of the reasons why research is being done to develop powerful and scalable clone detection techniques. In this thesis, a new clone detection method is presented that uses paths and path sets derived from the dominator trees of the functions to detect the code clones. A dominator tree is a special form of the control ïŹow graph, which does not contain cycles. The dominator tree based method has been implemented in the StoneDetector tool and can detect code clones in Java source code as well as in Java bytecode. It has equally good or better recall and precision results than previously published code clone detection methods. The evaluation was performed using the BigCloneBench. Scalability measurements showed that even source code with several 100 million lines of code can be searched in a reasonable time. In order to evaluate the bytecode based StoneDetector variant, the BigCloneBench ïŹles had to be compiled. For this purpose, the Stubber tool was developed, which can compile Java source code ïŹles without the required libraries. Finally, it could be shown that using the register code generated from the Java bytecode, similar recall and precision values could be achieved compared to the source code based variant. Since some machine learning studies specify that very good recall and precision values can be achieved for all clone types, a machine learning method was trained with dominator trees. It could be shown that the results published by the studies are not reproducible on unseen data.Wird eine bestehende Funktion in einem Softwareprojekt kopiert und (in leicht angepasster Form) erneut genutzt, entsteht ein Codeklon. War in der ursprĂŒnglichen Funktion jedoch ein Fehler oder eine Schwachstelle, so ist dieser Fehler beziehungsweise diese Schwachstelle jetzt an mehreren Stellen im Softwareprojekt enthalten. Dies ist einer der GrĂŒnde, weshalb an der Entwicklung von leistungsstarken und skalierbaren Klonerkennungsverfahren geforscht wird. In der hier vorliegenden Arbeit wird ein neues Klonerkennungsverfahren vorgestellt, das zum Detektieren der Codeklone Pfade und Pfadmengen nutzt, die aus den DominatorbĂ€umen der Funktionen abgeleitet werden. Ein Dominatorbaum wird aus dem Kontrollflussgraphen abgeleitet und enthĂ€lt keine Zyklen. Das Dominatorbaum-basierte Verfahren wurde in dem Werkzeug StoneDetector umgesetzt und kann Codeklone sowohl im Java-Quelltext als auch im Java-Bytecode detektieren. Dabei hat es gleich gute oder bessere Recall- und Precision-Werte als bisher veröffentlichte Codeklonerkennungsverfahren. Die Wert-Evaluierungen wurden dabei unter Verwendung des BigClone-Benchs durchgefĂŒhrt. Skalierbarkeitsmessungen zeigten, dass sogar Quellcodedateien mit mehreren 100-Millionen Codezeilen in angemessener Zeit durchsucht werden können. Damit die Bytecode-basierte StoneDetector-Variante auch evaluiert werden konnte, mussten die Dateien des BigCloneBench kompiliert werden. Dazu wurde das Stubber-Tool entwickelt, welches Java-Quelltextdateien ohne die benötigten AbhĂ€ngigkeiten kompilieren kann. Schlussendlich konnte somit gezeigt werden, dass mithilfe des aus dem Java-Bytecode generierten Registercodes Ă€hnliche Recall- und Precision-Werte im Vergleich zu der Quelltext-basierten Variante erreicht werden können. Da einige Arbeiten mit maschinellen Lernverfahren angeben, bei allen Klontypen sehr gute Recall- und Precision-Werte zu erreichen, wurde ein maschinelles Lernverfahren mit DominatorĂ€umen trainiert. Es konnte gezeigt werden, dass die von den Arbeiten veröffentlichten Ergebnisse nicht auf ungesehenen Daten reproduzierbar sind
Distribution of Scattering Matrix Elements in Quantum Chaotic Scattering
Scattering is an important phenomenon which is observed in systems ranging
from the micro- to macroscale. In the context of nuclear reaction theory the
Heidelberg approach was proposed and later demonstrated to be applicable to
many chaotic scattering systems. To model the universal properties,
stochasticity is introduced to the scattering matrix on the level of the
Hamiltonian by using random matrices. A long-standing problem was the
computation of the distribution of the off-diagonal scattering-matrix elements.
We report here an exact solution to this problem and present analytical results
for systems with preserved and with violated time-reversal invariance. Our
derivation is based on a new variant of the supersymmetry method. We also
validate our results with scattering data obtained from experiments with
microwave billiards.Comment: Published versio
Donor-Stabilized Monocarba-Bridged Bis(cyclopentadienyl)alanes
Five monocarba-bridged bis(cyclopentadienyl)aluminum halide NHC and thione complexes and one monocarba-bridged bis(cyclopentadienyl)phosphanylalane NHC complex are reported. The former were synthesized by transmetalation of a C[1]magnesocenophane with the corresponding aluminum(III) chloride and aluminum(III) bromide donor adducts. The phosphanylalane complex was obtained by a subsequent functionalization of the corresponding bromoalane with lithium diphenylphosphide. All complexes were characterized in solution by multinuclear NMR spectroscopy and in the solid state by single crystal X-ray diffraction. Bonding energies of the NHC and thione ligands to the aluminum centres were estimated by DFT calculations
Constrained Geometry ansa âHalfâSandwich Complexes of Magnesium â Versatile sâBlock Catalysts
The synthesis, characterization and catalytic application of a
series of constrained geometry ansa-half-sandwich complexes
of magnesium is reported. These versatile s-block catalysts were
applied in different dehydrocoupling and hydroelementation
reactions, demonstrating a broad applicability with particularly
remarkable performance in dehydrocoupling reactions
Monitorização do processo de condução e alertas baseados no contexto
Motivação e visĂŁo geral do sistema: A fadiga Ă© considerada como um dos principais fatores responsĂĄvel pela sinistralidade rodoviĂĄria. Uma agĂȘncia norte-americana estimou, em 2013, que condutores com sonolĂȘncia causada pela fadiga provocaram mais de 70 mil acidentes, resultando mais de 40 mil feridos e cerca de 800 mortos. 4 Tipicamente, para realizar a deteção destes aspetos Ă© realizado processamento de imagem, como por exemplo, da retina. PorĂ©m, Ă© possĂvel utilizar outras abordagens, nomeadamente os sinais fisiolĂłgicos como Ă© feito pelo Cardiowheel. O CardioWheel Ă© um sistema embebido integrĂĄvel em automĂłveis, tem como objetivo detetar automaticamente estados de fadiga e a identidade biomĂ©trica. Para tal Ă© medido no volante um elemento biomĂ©trico do condutor, o sinal cardĂaco, e emitidos alertas de fadiga para o exterior atravĂ©s de comunicaçÔes por GPRS.info:eu-repo/semantics/publishedVersio
Camouflaged galactic CMB foregrounds: total and polarized contributions of the kinetic Sunyaev Zeldovich effect
We consider the role of the galactic kinetic Sunyaev Zeldovich (SZ) effect as
a CMB foreground. While the galactic thermal Sunyaev Zeldovich effect has
previously been studied and discarded as a potential CMB foreground, we find
that the kinetic SZ effect is dominant in the galactic case. We analyse the
detectability of the kinetic SZ effect by means of an optimally matched filter
technique applied to a simulation of an ideal observation. We obtain no
detection, getting a S/N ratio of 0.1, thereby demonstrating that the kinetic
SZ effect can also safely be ignored as a CMB foreground. However we provide
maps of the expected signal for inclusion in future high precision data
processing. Furthermore, we rule out the significant contamination of the
polarised CMB signal by second scattering of galactic kinetic Sunyaev-Zeldovich
photons, since we show that the scattering of the CMB quadrupole photons by
galactic electrons is a stronger effect than the Sunyaev Zeldovich second
scattering, and has already been shown to produce no significant polarised
contamination. We confirm the latter assessment also by means of an optimally
matched filter.Comment: 9 pages, 6 figures, 2 tables. submitte
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