dotCall64: An Efficient Interface to Compiled C/C++ and Fortran Code Supporting Long Vectors

The R functions .C() and .Fortran() can be used to call compiled C/C++ and Fortran code from R. This so-called foreign function interface is convenient, since it does not require any interactions with the C API of R. However, it does not support long vectors (i.e., vectors of more than 2^31 elements). To overcome this limitation, the R package dotCall64 provides .C64(), which can be used to call compiled C/C++ and Fortran functions. It transparently supports long vectors and does the necessary castings to pass numeric R vectors to 64-bit integer arguments of the compiled code. Moreover, .C64() features a mechanism to avoid unnecessary copies of function arguments, making it efficient in terms of speed and memory usage.Comment: 17 page

Force-dependent unbinding rate of molecular motors from stationary optical trap data

Molecular motors walk along filaments until they detach stochastically with a force-dependent unbinding rate. Here, we show that this unbinding rate can be obtained from the analysis of experimental data of molecular motors moving in stationary optical traps. Two complementary methods are presented, based on the analysis of the distribution for the unbinding forces and of the motor's force traces. In the first method, analytically derived force distributions for slip bonds, slip-ideal bonds, and catch bonds are used to fit the cumulative distributions of the unbinding forces. The second method is based on the statistical analysis of the observed force traces. We validate both methods with stochastic simulations and apply them to experimental data for kinesin-1

Fourth-Order Perturbation Theory for the Half-Filled Hubbard Model in Infinite Dimensions

We calculate the zero-temperature self-energy to fourth-order perturbation theory in the Hubbard interaction $U$ for the half-filled Hubbard model in infinite dimensions. For the Bethe lattice with bare bandwidth $W$, we compare our perturbative results for the self-energy, the single-particle density of states, and the momentum distribution to those from approximate analytical and numerical studies of the model. Results for the density of states from perturbation theory at $U/W=0.4$ agree very well with those from the Dynamical Mean-Field Theory treated with the Fixed-Energy Exact Diagonalization and with the Dynamical Density-Matrix Renormalization Group. In contrast, our results reveal the limited resolution of the Numerical Renormalization Group approach in treating the Hubbard bands. The momentum distributions from all approximate studies of the model are very similar in the regime where perturbation theory is applicable, $U/W \le 0.6$. Iterated Perturbation Theory overestimates the quasiparticle weight above such moderate interaction strengths.Comment: 19 pages, 17 figures, submitted to EPJ

Analytical and Numerical Treatment of the Mott--Hubbard Insulator in Infinite Dimensions

We calculate the density of states in the half-filled Hubbard model on a Bethe lattice with infinite connectivity. Based on our analytical results to second order in $t/U$, we propose a new `Fixed-Energy Exact Diagonalization' scheme for the numerical study of the Dynamical Mean-Field Theory. Corroborated by results from the Random Dispersion Approximation, we find that the gap opens at $U_{\rm c}=4.43 \pm 0.05$. Moreover, the density of states near the gap increases algebraically as a function of frequency with an exponent $\alpha=1/2$ in the insulating phase. We critically examine other analytical and numerical approaches and specify their merits and limitations when applied to the Mott--Hubbard insulator.Comment: 22 pages, 16 figures; minor changes (one reference added, included comparison with Falicov-Kimball model

Wirkung bewegungsinduzierender Sitzmöbel im Unterricht auf die Lösungsfähigkeit bei Algebra und die Befindlichkeit

Die kognitive Leistungsfähigkeit ist eine grundlegende Voraussetzung für die Bewältigung von Lerninhalten, die im Schulunterricht vermittelt werden. Wissenschaftliche Studien belegen eine enge Verbindung von Motorik und Kognition (z. B. Laufer, Ashkenazi & Josman, 2008), wobei unterschiedliche Fragestellungen, wie etwa der Einfluss des Alters oder die Art der motorisch-kognitiven Aufgaben ein weites Forschungsfeld eröffnen und unterschiedliche Schlussfolgerungen über den Zusammenhang zulassen (vgl. Szturm et al., 2013; Makizako, Furuna, Ihira & Shimada, 2013; Van Impe et al., 2012). In der vorliegenden Studie wurde, basierend auf der Grundannahme einer positiven Wirkung auf die kognitive Leistungsfähigkeit durch Bewegungsinduktion während des Sitzens (vgl. Maus, Henz & Schöllhorn, 2013), die Leistung bei Algebra sowie die subjektive Einschätzung der Befindlichkeit unter bewegtem und statischem Sitzen getestet