2,025 research outputs found
R&D Investments Under Endogenous Cluster Formation
No full textDawid H, Hellmann T. R&D Investments Under Endogenous Cluster Formation. Journal of Economic Behavior and Organization. 2020;174:253-283
The Evolution of R&D Networks
No full textDawid H, Hellmann T. The Evolution of R&D Networks. Journal of Economic Behavior and Organization. 2014;105:158-172.We study the evolution of R&D networks in a Cournot model whererms may lower marginal costs due to bilateral R&D collaborations. Stochastically stable R&D networks exhibit the dominant group architecture, and, contrary to the existing literature, generically unique predictions about the size of the dominant group can be obtained. This size decreases monotonically with respect to the cost of link formation and there exists a lower bound on the size of the dominant group for non-empty networks. Stochastically stable networks are always inefficient and an increase in linking costs has a non-monotone effect on average industry profits
Salinization Processes in the Venetian Coastal Plain (Italy): A General Overview
No full textDue to its location near the Venice Lagoon and the Adriatic Sea, as well anthropogenic pressure, the Venetian inland is a densely populated area undergoing salinization processes of soil and groundwater. This strongly affects the economical and social development of the area, in particular agricultural and touristic activities, and the weathering of building materials in urban settlements. This research aims at assessing the present degree of subsoil and groundwater salinization, and identifying critical conditions in relation to economic activities such as agriculture and tourism
Sul teorema di Hellmann-Feynman
No full textNella prima parte di questo paper verrà dimostrato il teorema di Hellmann-Feynman (H-F) su autostati esatti. Nella seconda, grazie ad esso, verranno ricavati i termini lineare e quadratico della serie perturbativa di uno spettro non-degenere. Nel terzo capitolo verrà dimostrato il teorema di H-F nel contesto del metodo variazionale di Rayleigh-Ritz. Infine, verrà presentata una semplice applicazione del teorema di H-F al calcolo del valore di aspettazione dell'operatore 1/r² per un atomo idrogenoide
Eosinophiles Granulom des Felsen- und Schläfenbeins. Fallbericht und Literaturübersicht
No full textHellmann M, Stein H, Ebmeyer J, Sudhoff H. Eosinophiles Granulom des Felsen- und Schläfenbeins. Fallbericht und Literaturübersicht. Laryngo-Rhino-Otologie. 2003;82(4):258-261
Relativistic Scattering States of the Hellmann Potential
No full textIn this letter, the scattering state solutions of the Dirac equation for spin and pseudospin symmetries are obtained for the Hellmann potential. The normalized wave functions and scattering phase shifts are calculated for both spin and pseudospin symmetries. Scattering properties for Coulomb-like and Yukawa-like potentials are also studied as limiting cases
[FE3W3S14]4-, A NOVEL HEXANUCLEAR, PURE BIMETAL-SULFUR CLUSTER WITH FE3(MU-3-S)2 CENTER
No full textMüller A, HELLMANN W, Bögge H, JOSTES R, Römer M, SCHIMANSKI U. [FE3W3S14]4-, A NOVEL HEXANUCLEAR, PURE BIMETAL-SULFUR CLUSTER WITH FE3(MU-3-S)2 CENTER. ANGEWANDTE CHEMIE-INTERNATIONAL EDITION IN ENGLISH. 1982;21(11):860-861
Feynman-Hellmann approach to the spin structure of hadrons
No full textWe perform a Nf=2+1 lattice QCD simulation to determine the quark spin fractions of hadrons using the Feynman-Hellmann theorem. By introducing an external spin operator to the fermion action, the matrix elements relevant for quark spin fractions are extracted from the linear response of the hadron energies. Simulations indicate that the Feynman-Hellmann method offers statistical precision that is comparable to the standard three-point function approach, with the added benefit that it is less susceptible to excited-state contamination. This suggests that the Feynman-Hellmann technique offers a promising alternative for calculations of quark line disconnected contributions to hadronic matrix elements. At the SU(3)-flavor symmetry point, we find that the connected quark spin fractions are universally in the range 55%–70% for vector mesons and octet and decuplet baryons. There is an indication that the amount of spin suppression is quite sensitive to the strength of SU(3) breaking
Renormalization group, trace anomaly and Feynman-Hellmann theorem
No full textWe show that the logarithmic derivative of the gauge coupling on the hadronic mass and the cosmological constant term of a gauge theory are related to the gluon condensate of the hadron and the vacuum respectively. These relations are akin to Feynman-Hellmann relations whose derivation for the case at hand are complicated by the construction of the gauge theory Hamiltonian. We bypass this problem by using a renormalisation group equation for composite operators and the trace anomaly. The relations serve as possible definitions of the gluon condensates themselves which are plagued in direct approaches by power divergences. In turn these results might help to determine the contribution of the QCD phase transition to the cosmological constant and test speculative ideas
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