Probing of valley polarization in graphene via optical second-harmonic generation

Valley polarization in graphene breaks inversion symmetry and therefore leads to second-harmonic generation. We present a complete theory of this effect within a single-particle approximation. It is shown that this may be a sensitive tool to measure the valley polarization created, e.g., by polarized light and, thus, can be used for a development of ultrafast valleytronics in graphene.Comment: 5 pages, 3 figure

A HIERARCHICAL BAYES APPROACH TO MODELING CHOICE DATA: A STUDY OF WETLAND RESTORATION PROGRAMS

This study examines the factors the influence the values and importance that landowners place on the attributes of voluntary wetland restoration programs. Choice-based conjoint analysis, a stated preference method, was used to estimate the marginal utilities and values for restoration program attributes for North Carolina landowners. Landowner preferences were estimated at individual and aggregate levels to examine the importance of modeling heterogeneous preferences. Choice modeling performed at both aggregate and individual levels demonstrated the information gains from a disaggregated approach.Research Methods/ Statistical Methods,

A gobal fit to the anomalous magnetic moment, Higgs limit and b->s gamma in the constrained MSSM

New data on the anomalous magnetic moment of the muon together with the b->s gamma decay rate and Higgs limits are considered within the supergravity inspired constrained minimal supersymmetric model. We perform a global statistical chi2 analysis of these data and show that the allowed region of parameter space is bounded from below by the Higgs limit, which depends on the trilinear coupling and from above by the anomalous magnetic moment.Comment: 3 pages, To appear in Proc. of SUSY01, Dubna (Russia

Statistical learning is not error-driven

Prediction errors have a prominent role in many forms of learning. For example, in reinforcement learning agents learn by updating the association between states and outcomes as a function of the prediction error elicited by the event. An empirical hallmark of such error-driven learning is Kamin blocking, whereby the association between a stimulus and outcome is only learnt when the outcome is not already fully predicted by another stimulus. It remains debated however to which extent error-driven computations underlie learning of automatically formed associations as in statistical learning. Here we asked whether the automatic and incidental learning of the statistical structure of the environment is error-driven, like reinforcement learning, or instead does not rely on prediction errors for learning associations. We addressed this issue in a series of Kamin blocking studies. In three consecutive experiments, we observed robust incidental statistical learning of temporal associations among pairs of images, but no evidence of blocking. Our results suggest that statistical learning is not error-driven but may rather follow the principles of basic Hebbian associative learning

Radiative-Recoil Corrections of Order α(Zα)5(m/M)m\alpha(Z\alpha)^5(m/M)m to Lamb Shift Revisited

The results and main steps of an analytic calculation of radiative-recoil corrections of order $\alpha(Z\alpha)^5(m/M)m$ to the Lamb shift in hydrogen are presented. The calculations are performed in the infrared safe Yennie gauge. The discrepancy between two previous numerical calculations of these corrections existing in the literature is resolved. Our new result eliminates the largest source of the theoretical uncertainty in the magnitude of the deuterium-hydrogen isotope shift.Comment: 14 pages, REVTE

Effective Ising model for correlated systems with charge ordering

Collective electronic fluctuations in correlated materials give rise to various important phenomena, such as existence of the charge ordering, superconductivity, Mott insulating and magnetic phases, plasmon and magnon modes, and other interesting features of such systems. Unfortunately, description of these correlation effects requires significant efforts, since they almost entirely rely on strong local and nonlocal electron-electron interactions. Some collective phenomena, such as magnetism, can be sufficiently described by a simple Heisenberg-like models that are formulated in terms of bosonic variables. This fact suggests that other many-body excitations can also be described by simple bosonic models in spirit of the Heisenberg theory. Here we derive an effective bosonic action for charge degrees of freedom for the extended Hubbard model and define a physical regime where the obtained action reduces to a classical Hamiltonian of an effective Ising model

Neurogene Stammzelltransplantation in die Kochlea

Zusammenfassung: Hintergrund: Die Stammzelltherapie ist insbesondere im Hinblick auf eine Applikation im Innenohr interessant, da die Haarzellen nicht regenerieren. Einmal abgestorbene Haarzellen werden nicht ersetzt, es kommt zu einem irreversiblen Hörverlust. In den vergangenen Jahren konnten Stammzellen mit wechselndem Erfolg ins Innenohr appliziert werden, zum Teil haben sie sich zu Innenohrzellen entwickelt. In der vorliegenden Studie wollten wir untersuchen, wie sich neuronale Vorläuferzellen verhalten, wenn sie in vitro und in vivo auf ein geschädigtes Innenohr aufgebracht werden. Methoden: Neuronale Vorläuferzellen wurden von E9,5Tage alten Mausembryonen isoliert und danach mit einem Virus, der das grün fluoreszierende Protein (GFP) exprimiert, infiziert. In der Folge wurden die GFP+-neuralen Vorläuferzellen sowohl auf ein geschädigtes Corti-Organ in vitro aufgebracht als auch Mäusen ins zuvor geschädigte Innenohr in vivo appliziert. Anschließend wurden die Vorläuferzellen bzw. ihr Bezug zum Corti-Organ analysiert. Ergebnisse: Sowohl auf ein geschädigtes Corti-Organ aufgebrachte GFP+-neurale Vorläuferzellen als auch in vivo in geschädigte Innenohren transplantierte GFP+-neurale Vorläuferzellen konnten nach Transplantation nachgewiesen werden. Interessanterweise haben sich die GFP+-neuralen Vorläuferzellen nicht zufällig auf dem Organ niedergelassen, sondern ein gewisses Muster gezeigt. Insbesondere konnte nach der In-vivo-Applikation gesehen werden, dass die GFP+-neuralen Vorläuferzellen sich im Bereich des Corti-Organs in der Region von abgestorbenen Haarzellen angesiedelt haben. Schlussfolgerung: Neuronale Vorläuferzellen haben ein großes Potenzial, einmal abgestorbene Haarzellen zu ersetzen. Allerdings braucht es noch intensive Forschung bis zur klinischen Anwendun