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Body size-dependent energy storage causes Kleiber's law scaling of the metabolic rate in planarians
Get PDFKleiber's law, or the 3/4-power law scaling of the metabolic rate with body mass, is considered one of the few quantitative laws in biology, yet its physiological basis remains unknown. Here, we report Kleiber's law scaling in the planarian Schmidtea mediterranea. Its reversible and life history-independent changes in adult body mass over 3 orders of magnitude reveal that Kleiber's law does not emerge from the size-dependent decrease in cellular metabolic rate, but from a size-dependent increase in mass per cell. Through a combination of experiment and theoretical analysis of the organismal energy balance, we further show that the mass allometry is caused by body size dependent energy storage. Our results reveal the physiological origins of Kleiber's law in planarians and have general implications for understanding a fundamental scaling law in biology
Strategies for mechanical metamaterial design
No full textOn a structural level, the properties featured by a majority of mechanical metamaterials can be ascribed to the finite number of soft internal degrees-of freedom allowing for low-energy deformations. Ideally, these low-energy deformation modes can be represented through mechanisms consisting of movable rigid geometrical units. Conversely, these mechanisms also serve as an intuitive starting point to initiate and adapt the design of mechanical metamaterials to requirements. Traditional design methods mainly comprising trial and testing can only well handle simple design tasks, not to mention that the final designs can be periodic and non-generic. In order to solve complex design problems, computer algorithm based inverse strategies provide state-of-the-art solutions. One way in which they can be utilized is by framing the material design problem as an optimization problem, where we optimize the values of control parameters (design variables) - in order to meet the desired target response. In this thesis, we present novel inverse strategies to design 2D mechanical metamaterials, whose zero-energy deformations can be modeled by one degree-of-freedom mechanisms consisting of pin-jointed polygons. We demonstrate that by optimizing the characteristic trajectory of these mechanisms, one can design generic metamaterials that exhibit complex programmable mechanics, atypical zero-energy deformations and shape-transformable behavior
Crystal Orientation and Grain Size: Do They Determine Optoelectronic Properties of MAPbI3 Perovskite?
Get PDFGrowing large, oriented grains of perovskite often leads to efficient devices, but it is unclear if properties of the grains are responsible for the efficiency. Domains observed in SEM are commonly misidentified with crystallographic grains, but SEM images do not provide diffraction information. We study methylammoinium lead iodide (MAPbI3) films fabricated via flash infrared annealing (FIRA) and the conventional antisolvent (AS) method by measuring grain size and orientation using electron back-scattered diffraction (EBSD) and studying how these affect optoelectronic properties such as local photoluminescence (PL), charge carrier lifetimes, and mobilities. We observe a local enhancement and shift of the PL emission at different regions of the FIRA clusters, but we observe no effect of crystal orientation on the optoelectronic properties. Additionally, despite substantial differences in grain size between the two systems, we find similar optoelectronic properties. These findings show that optoelectronic quality is not necessarily related to the orientation and size of crystalline domains
Plasmon antenna array "patchwork" lasers - towards low etendue, speckle free light sources
Get PDFIn this work, we study plasmon antenna array lasers for solid-state lighting (SSL). Optically pumped plasmon antenna array lasers can provide benefits suitable for SSL including efficient pump-light absorption, high brightness, and good directivity. However, applying lasers in SSL is difficult because of speckle formation. To overcome this issue, we propose two types of lasers based on patchworks of small plasmon lattices with different lattice constants, tessellating an extended surface. The premise is that they could ultimately form a blue-LED pumped broad-area directional emitter with reduced coherence to suppress speckle. An important question is whether different patches couple when assembled together, and how this affects spatial and spectral profiles. In this paper, we show measurement results on the plasmon patchwork lasers, and discuss their modelling and potential application as low etendue and speckle free sources in SSL
Application and validity of the effective medium approximation to the optical properties of nano-textured silicon coated with a dielectric layer
Get PDFThe emergence of nanotextures in photovoltaics has resulted in challenges associated with optical modelling. Whilst rigorous methods exist to accurately solve these textures, the computational effort required limits the scope of modeling applications. The effective medium approximation (EMA) is a potential alternative to provide rapid modeling results which can be easily integrated with ray tracing of large complex structures. However, the validity of this technique is strongly dependent on the size of features relative to the wavelength of interest, making the application of EMA ambiguous for many situations. This paper aims to address this issue by comparing the simulated results between EMA and finite element methods for three randomly distributed silicon textures with and without a dielectric layer. Criteria for which the EMA approach is valid are proposed and generalized using ratios between root-mean-square roughness, correlation length and incident wavelength, making these limits broadly applicable, beyond that of just the nanotexture under specific solar spectrum regimes. The results in this work apply to random, isotropic textures under normally incident light. Based on the proposed criteria, the validity of different optical simulation techniques for a set of industrial photovoltaic textures is discussed. This analysis reveals a region within which neither geometric optics nor EMA are adequate for calculating the reflectivity of a textured surface, and hence FDTD or other new approaches are required
Vibrational Relaxation Dynamics of the Core and Outer Part of Proton-Hydration Clusters
Get PDFWe study the ultrafast relaxation dynamics of hydrated proton clusters in acetonitrile using femtosecond mid-infrared pump-probe spectroscopy. We observe a strong dependence of transient absorption dynamics on the frequency of excitation. When we excite the OH vibrations with frequencies ≤3100 cm-1 we observe an ultrafast energy relaxation that leads to heating of the local environment of proton. This response is assigned to the OH vibrations of the water molecules in the core of the hydrated proton cluster. When we excite with frequencies ≥3200 cm-1 we observe a relatively slow vibrational relaxation with a T1 time constant ranging from 0.22±0.04 ps at νex=3200 cm-1 to 0.37±0.02 ps at νex=3520 cm-1. We assign this response to water molecules in the outer part of the hydrated proton cluster
Spatial resolution of coherent cathodoluminescence super-resolution microscopy
Get PDFWe investigate the nanoscale excitation of Ag nanocubes with coherent cathodoluminescence imaging spectroscopy (CL) to resolve the factors that determine the spatial resolution of CL as a deep-subwavelength imaging technique. The 10–30 keV electron beam coherently excites localized plasmons in 70 nm Ag cubes at 2.4 and 3.1 eV. The radiation from these plasmon modes is collected in the far-field together with the secondary electron intensity. CL line scans across the nanocubes show exponentially decaying tails away from the cube that reveal the evanescent coupling of the electron field to the resonant plasmon modes. The measured CL decay lengths range from 8 nm (10 keV) to 12 nm (30 keV) and differ from the calculated ones by only 1–3 nm. A statistical model of electron scattering inside the Ag nanocubes is developed to analyze the secondary electron images and compare them with the CL data. The Ag nanocube edges are derived from the CL line scans with a systematic error less than 3 nm. The data demonstrate that CL probes the electron-induced plasmon fields with nanometer accuracy
Design and fabrication of a hybrid alginate hydrogel/poly(ε‐caprolactone) mold for auricular cartilage reconstruction
Get PDFThe aim of this study was to design and manufacture an easily assembled cartilage implant model for auricular reconstruction. First, the printing accuracy and mechanical properties of 3D‐printed poly‐ε‐caprolactone (PCL) scaffolds with varying porosities were determined to assess overall material properties. Next, the applicability of alginate as cell carrier for the cartilage implant model was determined. Using the optimal outcomes of both experiments (in terms of (bio)mechanical properties, cell survival, neocartilage formation, and printing accuracy), a hybrid auricular implant model was developed. PCL scaffolds with 600 μm distances between strands exhibited the best mechanical properties and most optimal printing quality for further exploration. In alginate, chondrocytes displayed high cell survival (~83% after 21 days) and produced cartilage‐like matrix in vitro. Alginate beads cultured in proliferation medium exhibited slightly higher compressive moduli (6 kPa) compared to beads cultured in chondrogenic medium (3.5 kPa, p > .05). The final auricular mold could be printed with 300 μm pores and high fidelity, and the injected chondrocytes survived the culture period of 21 days. The presented hybrid auricular mold appears to be an adequate model for cartilage tissue engineering and may provide a novel approach to auricular cartilage regeneration for facial reconstruction
