Experiments on transformation thermodynamics: Molding the flow of heat

It has recently been shown theoretically that the time-dependent heat conduction equation is form-invariant under curvilinear coordinate transformations. Thus, in analogy to transformation optics, fictitious transformed space can be mapped onto (meta-)materials with spatially inhomogeneous and anisotropic heat-conductivity tensors in the laboratory space. On this basis, we design, fabricate, and characterize a micro-structured thermal cloak that molds the flow of heat around an object in a metal plate. This allows for transient protection of the object from heating, while maintaining the same downstream heat flow as without object and cloak.Comment: 10 pages, 4 figure

Hall-effect sign-inversion in a realizable 3D metamaterial

In 2009, Briane and Milton proved mathematically the existence of three-dimensional isotropic metamaterials with a classical Hall coefficient which is negative with respect to that of all of the metamaterial constituents. Here, we significantly simplify their blueprint towards an architecture composed of only a single constituent material in vacuum/air, which can be seen as a special type of porosity. We show that the sign of the Hall voltage is determined by a separation parameter between adjacent tori. This qualitative behavior is robust even for only a small number of metamaterial unit cells. The combination of simplification and robustness brings experimental verifications of this striking sign-inversion into reach.Comment: 9 figures, 7 page

On three-dimensional dilational elastic metamaterials

Dilational materials are stable three-dimensional isotropic auxetics with an ultimate Poisson's ratio of -1. We design, evaluate, fabricate, and characterize crystalline metamaterials approaching this ideal. To reveal all modes, we calculate the phonon band structures. On this basis, using cubic symmetry, we can unambiguously retrieve all different non-zero elements of the rank-4 effective metamaterial elasticity tensor, from which all effective elastic metamaterial properties follow. While the elastic properties and the phase velocity remain anisotropic, the effective Poisson's ratio indeed becomes isotropic and approaches -1 in the limit of small internal connections. This finding is also supported by independent static continuum-mechanics calculations. In static experiments on macroscopic polymer structures fabricated by three-dimensional printing, we measure Poisson's ratios as low as -0.8 in good agreement with theory. Microscopic samples are also presented.Comment: 8 figure

Phonon band structures of three-dimensional pentamode metamaterials

Three-dimensional pentamode metamaterials are artificial solids that approximately behave like liquids, which have vanishing shear modulus. Pentamodes have recently become experimental reality. Here, we calculate their phonon band structures for various parameters. Consistent with static continuum mechanics, we find that compression and shear waves exhibit phase velocities that can realistically be different by more than one order of magnitude. Interestingly, we also find frequency intervals with more than two octaves bandwidth in which pure single-mode behavior is obtained. Herein, exclusively compression waves exist due to a complete three-dimensional band gap for shear waves and, hence, no coupling to shear modes is possible. Such single-mode behavior might, e.g., be interesting for transformation-elastodynamics architectures.Comment: 5 figure

Removal of a Conserved Disulfide Bond Does Not Compromise Mechanical Stability of a VHH Antibody Complex

Single-domain VHH antibodies are promising reagents for medical therapy. A conserved disulfide bond within the VHH framework region is known to be critical for thermal stability, however, no prior studies have investigated its influence on the stability of VHH antibody–antigen complexes under mechanical load. Here, we used single-molecule force spectroscopy to test the influence of a VHH domain’s conserved disulfide bond on the mechanical strength of the interaction with its antigen mCherry. We found that although removal of the disulfide bond through cysteine-to-alanine mutagenesis significantly lowered VHH domain denaturation temperature, it had no significant impact on the mechanical strength of the VHH:mCherry interaction with complex rupture occurring at ∼60 pN at 103–104 pN/sec regardless of disulfide bond state. These results demonstrate that mechanostable binding interactions can be built on molecular scaffolds that may be thermodynamically compromised at equilibrium

Loss of β1-integrin-deficient cells during the development of endoderm-derived epithelia

β1-Integrins (β1) represent cell surface receptors which mediate cell-matrix and cell-cell interactions. Fässler and Meyer described chimeric mice containing transgenic cells that express the LacZ gene instead of the β1 gene. They observed β1-negative cells in all germ layers at embryonic day E8.5. Later in development, using a glucose phosphate isomerase assay of homogenized tissue samples, high levels of transgenic cells were found in skeletal muscle and gut, low levels in lung, heart, and kidney and none in the liver and spleen (Fässler and Meyer 1995). In order to study which cell types require β1 during development of the primitive gut including its derivatives, chimeric fetuses containing 15 to 25% transgenic cells were obtained at days E14.5 and E15.5. They were LacZ (β-galactosidase) stained "en bloc” and cross-sectioned head to tail. In esophagus, trachea, lung, stomach, hindgut, and the future urinary bladder, we observed various mesoderm-derived β1-negative cells (e.g. fibroblasts, chondrocytes, endothelial cells, and smooth muscle cells) but no β1-negative epithelial cells. Since the epithelia of lung, esophagus, trachea, stomach, hindgut, and urinary bladder are derived from the endodermal gut tube, we hypothesize that β1 is essential for the development and/or survival of the epithelia of the fore- and hindgut and its derivative

Small angle x-ray scattering with edge-illumination

Sensitivity to sub-pixel sample features has been demonstrated as a valuable capability of phase contrast x-ray imaging. Here, we report on a method to obtain angular-resolved small angle x-ray scattering distributions with edge-illumination- based imaging utilizing incoherent illumination from an x-ray tube. Our approach provides both the three established image modalities (absorption, differential phase and scatter strength), plus a number of additional contrasts related to unresolved sample features. The complementarity of these contrasts is experimentally validated by using different materials in powder form. As a significant application example we show that the extended complementary contrasts could allow the diagnosis of pulmonary emphysema in a murine model. In support of this, we demonstrate that the properties of the retrieved scattering distributions are consistent with the expectation of increased feature sizes related to pulmonary emphysema. Combined with the simplicity of implementation of edge-illumination, these findings suggest a high potential for exploiting extended sub-pixel contrasts in the diagnosis of lung diseases and beyond