Bending Behavior of Hybrid Timber-Steel Beams

Driven by climate change and the need for a more sustainable construction sector, policy is increasingly demanding and promoting timber hybrid construction methods. In the German state of Baden-Württemberg, every new public building has to be of timber or timber hybrid construction (Holzbauoffensive BW). The objective of multi-story buildings with large floor spans can only be achieved in a resource-efficient way by hybrid constructions combining timber and steel components. A research project recently completed at the Karlsruhe Institute of Technology was aimed at the development and systematic investigation of hybrid bending beams in which an advantageous combination of the materials steel and timber is used. For this purpose, steel profiles are integrated into timber cross-sections in a shear-resistant manner by adhesive bonding. As part of the experimental, numerical and analytical investigations, different cross-sections of steel and timber, as well as different construction materials, were considered (GL24h, LVL48p, LVL80p, S355 and S420). The results of large-scale four-point bending tests illustrate the potential of this new hybrid construction method. Depending on the geometry and material combinations tested, the bending stiffness could be increased by up to 250%, and the load-carrying capacity by up to 120%, compared to a glulam beam with identical dimensions.

Damping Properties of Large-Scale Overlap Joints Bonded with Epoxy Hybrid Resin or Polyurethanes: Experimental Characterisation and Analytical Description

Structures in various industries are exposed to dynamic loads. The dissipative properties of adhesively bonded joints can contribute to the damping of dynamically stressed structures. Dynamic hysteresis tests are carried out to determine the damping properties of adhesively bonded overlap joints by varying the geometry and test boundary conditions. The dimensions of the overlap joints are full-scale and thus relevant for steel construction. Based on the results of experimental investigations, a methodology is developed for the analytic determination of the damping properties of adhesively bonded overlap joints for various specimen geometries and stress boundary conditions. For this purpose, dimensional analysis is carried out using the Buckingham Pi Theorem. In summary, it can be stated that the loss factor of adhesively bonded overlap joints investigated within this study is in the range between 0.16 and 0.41. The damping properties can particularly be increased by increasing the adhesive layer thickness and reducing the overlap length. The functional relationships of all the test results shown can be determined by dimensional analysis. An analytical determination of the loss factor considering all identified influencing factors is enabled by derived regression functions with a high coefficient of determination.

Nonlinear self-trapping of matter waves in periodic potentials

We report the first experimental observation of nonlinear self-trapping of Bose-condensed 87Rb atoms in a one-dimensional waveguide with a superimposed deep periodic potential . The trapping effect is confirmed directly by imaging the atomic spatial distribution. Increasing the nonlinearity we move the system from the diffusive regime, characterized by an expansion of the condensate, to the nonlinearity dominated self-trapping regime, where the initial expansion stops and the width remains finite. The data are in quantitative agreement with the solutions of the corresponding discrete nonlinear equation. Our results reveal that the effect of nonlinear self-trapping is of local nature, and is closely related to the macroscopic self-trapping phenomenon already predicted for double-well systems.

Bright Bose-Einstein gap solitons of atoms with repulsive interaction

We report on the first experimental observation of bright matter wave solitons for 87Rb atoms with repulsive atom-atom interaction. This counterintuitive situation arises inside a weak periodic potential, where anomalous dispersion can be realized at the Brillouin zone boundary. If the coherent atomic wave packet is prepared at the corresponding band edge, a bright soliton is formed inside the gap. The strength of our system is the precise control of preparation and real time manipulation, allowing the systematic investigation of gap solitons.

Linear and nonlinear dynamics of matter wave packets in periodic potentials

We investigate experimentally and theoretically the nonlinear propagation of 87Rb Bose Einstein condensates in a trap with cylindrical symmetry. An additional weak periodic potential which encloses an angle with the symmetry axis of the waveguide is applied. The observed complex wave packet dynamics results from the coupling of transverse and longitudinal motion. We show that the experimental observations can be understood applying the concept of effective mass, which also allows to model numerically the three dimensional problem with a one dimensional equation. Within this framework the observed slowly spreading wave packets are a consequence of the continuous change of dispersion. The observed splitting of wave packets is very well described by the developed model and results from the nonlinear effect of transient solitonic propagation.

Dispersion management for atomic matter waves

We demonstrate the control of the dispersion of matter wave packets utilizing periodic potentials. This is analogous to the technique of dispersion management known in photon optics. Matter wave packets are realized by Bose-Einstein condensates of 87Rb in an optical dipole potential acting as a one-dimensional waveguide. A weak optical lattice is used to control the dispersion relation of the matter waves during the propagation of the wave packets. The dynamics are observed in position space and interpreted using the concept of effective mass. By switching from positive to negative effective mass, the dynamics can be reversed. The breakdown of the approximation of constant, as well as experimental signatures of an infinite effective mass are studied.

Selective enrichment and biochemical characterization of seven human skin fibroblasts cell types in vitro

The mitotic and postmitotic populations of the human skin fibroblast cell line HH-8 are heterogeneous when studied in vitro. There are reproducible changes in the frequencies of the mitotic fibroblasts (MF), MF I, MF II, MF III, and the postmitotic fibroblasts (PMF), PMF IV, PMF V, PMF VI, and PMF VII. For biochemical characterization, methods for selective enrichment of homogeneous populations of these seven fibroblast cell types have been established. Clonal populations with 95% purity for the mitotic fibroblasts MF I, MF II, and MF III can be raised in uniform clone types of fibroblasts (CTF) CTF I, CTF II, and CTF III. Pure clonal subpopulations of MF I type cells are present in mass populations in the range of 1-20 cumulative population doublings (CPD). Populations of mitotic fibroblasts represent nearly homogeneous populations of MF II (75-85% purity) in the range of 28-34 CPD and MF III (73-86% purity) in the range of 48-53 CPD. These populations can be easily expanded to up to 10(7)-10(8) cells. The spontaneous transition of MF III to PMF VI takes 140-180 days. In order to shorten this period and increase the proportion of distinct postmitotic types, mitotic fibroblast mass populations (CPD 30-32, MF II: 75-85% purity) have been induced by uv-irradiation to differentiate to nearly homogeneous populations of PMF IV, PMF V, PMF VI, and PMF VII within 4 to 36 days of culture. Using this method, 10(7) cells of one differentiation stage can be obtained. Spontaneously arising and experimentally selected or induced homogeneous clonal and mass populations of MF I, MF II, MF III, PMF IV, PMF V, PMF VI, and PMF VII express an identical differentiation-dependent and cell-type-specific [35S]methionine-labeled polypeptide pattern.

Human skin fibroblasts in vitro differentiate along a terminal cell lineage

Secondary mitotic human skin fibroblast populations in vitro underwent 53 +/- 6 cumulative population doublings (CPD) in 302 +/- 27 days. When the growth capacity of the mitotic fibroblasts is exhausted, and if appropriate methods are applied, the fibroblasts differentiate spontaneously into postmitotic fibroblast populations, which were kept in stationary culture for up to 305 +/- 41 additional days. Mitotic and postmitotic fibroblast populations are heterogeneous populations with reproducible changes in the proportions of mitotic fibroblasts F I, F II, and F III, and postmitotic fibroblasts F IV, F V, F VI, and F VII. This process makes it evident that the fibroblasts differentiate spontaneously along a seven-stage terminal cell lineage F I-F II-F III-F IV-F V-F VI-F VII. Shifts in the frequencies of the mitotic and postmitotic fibroblasts in mass populations are accompanied by alterations in the [35S]methionine polypeptide pattern of the developing mass populations. The [35S]methionine polypeptide patterns of homogeneous subpopulations of F I, F II, F III, F IV, F V, and F VI isolated from heterogeneous mass populations reveal that the six fibroblast morphotypes studied express their cell-type-specific [35S]methionine polypeptide pattern in the heterogeneous mass populations.