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The recent advances in state estimation, perception, and navigation algorithms have significantly contributed to the ubiquitous use of quadrotors for inspection, mapping, and aerial imaging. To further increase the versatility of quadrotors, recent works investigated the use of an adaptive morphology, which consists of modifying the shape of the vehicle during flight to suit a specific task or environment. However, these works either increase the complexity of the platform or decrease its controllability. In this letter, we propose a novel, simpler, yet effective morphing design for quadrotors consisting of a frame with four independently rotating arms that fold around the main frame. To guarantee stable flight at all times, we exploit an optimal control strategy that adapts on the fly to the drone morphology. We demonstrate the versatility of the proposed adaptive morphology in different tasks, such as negotiation of narrow gaps, close inspection of vertical surfaces, and object grasping and transportation. The experiments are performed on an actual, fully autonomous quadrotor relying solely on onboard visual-inertial sensors and compute. No external motion tracking systems and computers are used. This is the first work showing stable flight without requiring any symmetry of the morphology.

Biodegradable magnesium (Mg) alloys combine the advantages of traditional metallic implants and biodegradable polymers, having high strength, low density, and a stiffness ideal for bone fracture fixation. A recently developed Mg-Ca-Sr alloy potentially possesses advantageous characteristics over other Mg alloys, such as slower degradation rates and minimal toxicity. In this study, the biocompatibility of this Mg-Ca-Sr alloy was investigated in a rat pin-placement model. Cylindrical pins were inserted in the proximal tibial metaphyses in pre-drilled holes orthogonal to the tibial axis. Implant and bone morphologies were investigated using μCT at 1, 3, and 6 weeks after implant placement. At the same time points, the surrounding tissue was evaluated using H&E, TRAP and Goldner's trichrome staining. Although gas bubbles were observed around the degrading implant at early time points, the bone remained intact with no evidence of microfracture. Principle findings also include new bone formation in the area of the implant, suggesting that the alloy is a promising candidate for biodegradable orthopedic implants.

A novel 3D printing method for voxel-by-voxel metal printing is presented. Hollow atomic force microscopy (AFM) cantilevers are used to locally supply metal ions in an electrochemical cell, enabling a localized electroplating reaction. By exploiting the deflection feedback of these probes, electrochemical 3D metal printing is, for the first time, demonstrated in a layer-by-layer fashion, enabling the fabrication of arbitrary-shaped geometries.

Hexagonal boron nitride (h-BN) nanomesh, a two-dimensional insulating monolayer, grown on the (111) surface of rhodium exhibits an intriguing hexagonal corrugation pattern with a lattice constant of 3.2 nm. Despite numerous experimental and theoretical studies no quantitative agreement has been found on some details of the adsorption geometry such as the corrugation amplitude. The issue highlights the differences in chemical and electronic environment in the strongly bound pore regions and the weakly bound wire regions of the corrugated structure. For reliable results it is important to probe the structure with a method that is intrinsically sensitive to the position of the atomic cores rather than the electron density of states. In this work, we determine the corrugation of h-BN nanomesh from angle- and energy-resolved photoelectron diffraction measurements with chemical state resolution. By combining the results from angle and energy scans and comparing them to multiple-scattering simulations true adsorbate-substrate distance can be measured with high precision, avoiding pitfalls of apparent topography observed in scanning probe techniques. Our experimental results give accurate values for the peak-to-peak corrugation amplitude (0.80 Å), the bonding distance to the substrate (2.20 Å) and the buckling of the boron and nitrogen atoms in the strongly bound pore regions (0.07 Å). These results are important for the development of theoretical methods that involve a quantitative description of van der Waals systems as required for the understanding of the physics of two-dimensional sp2 layers.

In this work, we introduce a new residual distribution (RD) framework for the design of bound-preserving high-resolution finite element schemes. The continuous and discontinuous Galerkin discretizations of the linear advection equation are modified to construct local extremum diminishing (LED) approximations. To that end, we perform mass lumping and redistribute the element residuals in a manner which guarantees the LED property. The hierarchical correction procedure for high-order Bernstein finite element discretizations involves localization to subcells and definition of bound-preserving weights for subcell contributions. Using strong stability preserving (SSP) Runge–Kutta methods for time integration, we prove the validity of discrete maximum principles under CFL-like time step restrictions. The low-order version of our method has roughly the same accuracy as the one derived from a piecewise (multi)-linear approximation on a submesh with the same nodal points. In high-order extensions, we use an element-based flux-corrected transport (FCT) algorithm which can be interpreted as a nonlinear RD scheme. The proposed LED corrections are tailor-made for matrix-free implementations which avoid the rapidly growing cost of matrix assembly for high-order Bernstein elements. The results for 1D, 2D, and 3D test problems compare favorably to those obtained with the best matrix-based approaches.

Epithelial organoids are simplified models of organs grown in vitro from embryonic and adult stem cells. They are widely used to study organ development and disease, and enable drug screening in patient‐derived primary tissues. Current protocols, however, rely on animal‐ and tumor‐derived basement membrane extract (BME) as a 3D scaffold, which limits possible applications in regenerative medicine. This prompted us to study how organoids interact with their matrix, and to develop a well‐defined hydrogel that supports organoid generation and growth. It is found that soft fibrin matrices provide suitable physical support, and that naturally occurring Arg‐Gly‐Asp (RGD) adhesion domains on the scaffold, as well as supplementation with laminin‐111, are key parameters required for robust organoid formation and expansion. The possibility to functionalize fibrin via factor XIII‐mediated anchoring also allows to covalently link fluorescent nanoparticles to the matrix for 3D traction force microscopy. These measurements suggest that the morphogenesis of budding intestinal organoids results from internal pressure combined with higher cell contractility in the regions containing differentiated cells compared to the regions containing stem cells. Since the fibrin/laminin matrix supports long‐term expansion of all tested murine and human epithelial organoids, this hydrogel can be widely used as a defined equivalent to BME. ISSN:0935-9648 ISSN:1521-4095

An ever increasing amount of robotic platforms are being equipped with a new generation of neuromorphic computing architectures. Neuromorphic computing systems represent a promising brain-inspired technology that use asynchronous pulses to encode, transmit, and process sensory signals, typically implemented in compact low-latency and low-power devices. However, although multiple examples of sensing and processing neuromorphic devices have been successfully deployed on robotic platforms, no example of event-based neuromorphic motor controller has been proposed yet. In this paper, we present an open-loop neuromorphic controller implemented using a full-custom spiking neural network VLSI chip interfaced to motors for performing position control. The proposed controller is based on biologically inspired principles by which the discharge of motor-neuron populations produces muscle contractions. Following these principles, we use the spikes of the silicon neurons present in the neuromorphic chip to encode the target position and drive the motors using Pulse Frequency Modulation (PFM) technique, rather than the more traditional Pulse Width Modulation (PWM) one.

In this paper, we will consider the modelling of problems in linear elasticity on thin plates by the models of Kirchhoff–Love and Reissner–Mindlin. A fundamental investigation for the Kirchhoff plate goes back to Morgenstern (Arch. Ration. Mech. Anal. 4:145–152, 1959) and is based on the two-energies principle of Prager and Synge. This was half a century ago. We will derive the Kirchhoff–Love model based on Morgenstern’s ideas in a rigorous way (including the proper treatment of boundary conditions). Our derivation provides insights (a) into the relation of the (1,1,0)-model with the (1,1,2)-model which differs by a quadratic term in the ansatz for the third component of the displacement field and (b) into the rôle of the shear correction factor. A further advantage of the approach by the two-energies principle is that the extension to the Reissner–Mindlin plate model becomes very transparent and easy. Our study includes plates with reentrant corners with any interior opening angle, Journal of Elasticity, 103 (1), ISSN:0374-3535, ISSN:1573-2681

In this note we solve a problem posed by Ball (in Philos Trans R Soc Lond Ser A 306(1496):557-611, 1982) about the uniqueness of smooth equilibrium solutions to boundary value problems for strictly polyconvex functionals, $$\mathcal {F}(u)=\int_\Omega f(\nabla u(x)) {\rm d}x\quad{\rm and}\quad u\vert_{\partial\Omega}=u_0,$$ where Ω is homeomorphic to a ball. We give several examples of non-uniqueness. The main example is a boundary value problem with at least two different global minimizers, both analytic up to the boundary. All these examples are suggested by the theory of minimal surfaces

The interaction of metals with carbon materials (and specifically with graphene) is of importance for various technological applications. In particular, the intercalation of alkali metals is believed to provide a means for tuning the electronic properties of graphene for device applications. While the macroscopic effects of such intercalation events can readily be studied, following the related processes at an atomic scale in detail and under well-defined experimental conditions constitutes a challenge. Here, we investigate in situ the adsorption and nucleation of the alkali metals K, Cs, and Li on free-standing graphene by means of low-energy electron point source microscopy. We find that alkali metals readily intercalate between the layers of bilayer graphene. In fact, the equilibrium distribution of K and Cs favors a much-higher particle density between the layers than on the single-layer graphene. We obtain a quantitative value for the difference of the free energy of the binding between these two domains. Our study is completed with a control experiment introducing Pd as a representative of the nonalkali metals. Now, we observe cluster formation in equal measure on both single-layer and bilayer graphene; however, there was no intercalation. Our investigations thus constitute the first in situ study of metal-atom sorption of different specificity on free-standing graphene.

Electrical interfacing with neural tissue is key to advancing diagnosis and therapies for neurological disorders, as well as providing detailed information about neural signals. A challenge for creating long‐term stable interfaces between electronics and neural tissue is the huge mechanical mismatch between the systems. So far, materials and fabrication processes have restricted the development of soft electrode grids able to combine high performance, long‐term stability, and high electrode density, aspects all essential for neural interfacing. Here, this challenge is addressed by developing a soft, high‐density, stretchable electrode grid based on an inert, high‐performance composite material comprising gold‐coated titanium dioxide nanowires embedded in a silicone matrix. The developed grid can resolve high spatiotemporal neural signals from the surface of the cortex in freely moving rats with stable neural recording quality and preserved electrode signal coherence during 3 months of implantation. Due to its flexible and stretchable nature, it is possible to minimize the size of the craniotomy required for placement, further reducing the level of invasiveness. The material and device technology presented herein have potential for a wide range of emerging biomedical applications., Advanced Materials, 30 (15), ISSN:0935-9648, ISSN:1521-4095

Crystals of NaPd 3 X 2 , (X = Si, Ge, Sn) were synthesized and their crystal structures investigated by single crystal X-ray diffraction. The previously reported structures of NaPd 3 Si 2 and NaPd 3 Sn 2 were confirmed. NaPd 3 Ge 2 was found to have a different unit cell from that originally reported; therefore the structure was solved. It is an orthorhombically distorted version of the hexagonal CeCo 3 Be 2 -type structure, in space group Imma , with cell parameters a = 7.244(1) A, b = 9.938(1) A, c = 5.767(2) A. The originally reported cell is explained through triple twinning of the true cell. The structure of NaPd 3 Ge 2 fits the trend of decreasing X–X dimerization as a function of increasing period from Si–Sn. All three compounds are metals showing weak diamagnetism with increasing resistivity from NaPd 3 Si 2 –NaPd 3 Sn 2 ; no superconductivity is observed down to 2 K.

Using classical molecular dynamics based on Lennard-Jones-like potentials, a mechanically stable YBa2Cu3O7 high Tc superconductor structure is generated. This process is controlled via interactive computer graphics. After doping atoms into or removing atoms from the sample using a recently implemented picking mechanism, the lattice oscillation energy is annihilated with a simulated annealing procedure. The remaining minimum ground state energy allows marking of the preferred doping location. Information on the doping mechanism is important because the magnetic and superconducting properties of these compounds depend very strongly on their oxygen content

We present an algorithm to estimate the rotational motion of an event camera. In contrast to traditional cameras, which produce images at a fixed rate, event cameras have independent pixels that respond asynchronously to brightness changes, with microsecond resolution. Our method leverages the type of information conveyed by these novel sensors (i.e., edges) to directly estimate the angular velocity of the camera, without requiring optical flow or image intensity estimation. The core of the method is a contrast maximization design. The method performs favorably against ground truth data and gyroscopic measurements from an Inertial Measurement Unit, even in the presence of very high-speed motions (close to 1000 deg/s).

Single-molecule fluorescence spectroscopy is a powerful approach for probing biomolecular structure and dynamics, including protein folding. For the investigation of nonequilibrium kinetics, Forster resonance energy transfer combined with confocal multiparameter detection has proven particularly versatile, owing to the large number of observables and the broad range of accessible timescales, especially in combination with rapid microfluidic mixing. However, a comprehensive kinetic analysis of the resulting time series of transfer efficiency histograms and complementary observables can be challenging owing to the complexity of the data. Here we present and compare three different methods for the analysis of such kinetic data: singular value decomposition, multivariate curve resolution with alternating least square fitting, and model-based peak fitting, where an explicit model of both the transfer efficiency histogram of each species and the kinetic mechanism of the process is employed. While each of these methods has its merits for specific applications, we conclude that model-based peak fitting is most suitable for a quantitative analysis and comparison of kinetic mechanisms.

International audience; no abstract

Unlike standard cameras that send intensity images at a constant frame rate, event-driven cameras asynchronously report pixel-level brightness changes, offering low latency and high temporal resolution (both in the order of micro-seconds). As such, they have great potential for fast and low power vision algorithms for robots. Visual tracking, for example, is easily achieved even for very fast stimuli, as only moving objects cause brightness changes. However, cameras mounted on a moving robot are typically non-stationary and the same tracking problem becomes confounded by background clutter events due to the robot ego-motion. In this paper, we propose a method for segmenting the motion of an independently moving object for event-driven cameras. Our method detects and tracks corners in the event stream and learns the statistics of their motion as a function of the robot's joint velocities when no independently moving objects are present. During robot operation, independently moving objects are identified by discrepancies between the predicted corner velocities from ego-motion and the measured corner velocities. We validate the algorithm on data collected from the neuromorphic iCub robot. We achieve a precision of ~ 90 % and show that the method is robust to changes in speed of both the head and the target., Comment: 7 pages, 6 figures

International audience; State of the art approaches for visual-inertial sensor fusion use filter-based or optimization-based algorithms. Due to the nonlinearity of the system, a poor initialization can have a dramatic impact on the performance of these estimation methods. Recently, a closed-form solution providing such an initialization was derived in [1]. That solution determines the velocity (angular and linear) of a monocular camera in metric units by only using inertial measurements and image features acquired in a short time interval. In this letter, we study the impact of noisy sensors on the performance of this closed-form solution. We show that the gyroscope bias, not accounted for in [1], significantly affects the performance of the method. Therefore, we introduce a new method to automatically estimate this bias. Compared to the original method, the new approach now models the gyroscope bias and is robust to it. The performance of the proposed approach is successfully demonstrated on real data from a quadrotor MAV.

A high permittivity composite is developed to enhance the brightness of stretchable electroluminescent displays. The unique two-step assembly process yields dense layers, in which the voids around the electroluminescent particles are filled with smaller high dielectric particles. A stretchable seven-segment display based on the composite is bright enough to be used under standard indoor lighting conditions.

International audience; ANalysis Of VAriance (ANOVA) is a common technique for computing a ranking of the input parameters in terms of their contribution to the output variance. Nevertheless, the variance is not an universal criterion for ranking variables, since non symmetric outputs could require higher order statistics for their description and analysis. In this work, we illustrate how third and fourth-order moments, i.e. skewness and kurtosis, respectively, can be decomposed mimicking the ANOVA approach. It is also shown how this decomposition is correlated to a Polynomial Chaos (PC) expansion leading to a simple strategy to compute each term. New sensitivity indices, based on the contribution to the skewness and kurtosis, are proposed. The outcome of the proposed analysis is depicted by considering several test functions. Moreover, the ranking of the sensitivity indices is shown to vary according to their statistics order. Furthermore, the problem of formulating a truncated polynomial representation of the original function is treated. Both the reduction of the number of dimensions and the reduction of the order of interaction between parameters are considered. In both cases, the impact on the reduction is assessed in terms of statistics, namely the probability density function. Feasibility of the proposed analysis in a real-case is then demonstrated by presenting the sensitivity analysis of the performances of a turbine cascade in an Organic Rankine Cycles (ORCs), in the presence of complex thermodynamic models and multiple sources of uncertainty.

Two-dimensional networks inspired by graphene are of prime importance in nanoscience. We present a computational study of an infinite molecular sheet confined on a water surface to assess its properties and formation mechanism. Terpyridine-based ligand molecules are interlinked by Zn ions to form an extended 2D metal-organic framework. We show that the network is stable on the water surface, and that the substrate affects the dynamic properties of the sheet, exhibiting a confining effect and flattening the sheet by 30%. We use metadynamics to characterize the process of network formation and breaking and determine an intra-network binding energy of 143 kJ mol−1. Based on this mechanistic insight we propose that the 2D network strength can be tuned by varying the rigidity of the ligand through its chemical structure.

An in situ method to study the behavior of alloys during rapid heating and cooling combining laser heating with synchrotron micro X-ray diffraction and high-speed imaging is presented. Near-spherical Ti-48Al specimens were melted using a laser-based heating system consisting of two diode lasers and subsequently rapidly solidified using a Cu support structure. The Al-rich Ti-48Al forms a fine grained dual phase alpha(2) + gamma microstructure. Upon solidification, the formation of the beta-phase is fully suppressed. Time-resolved peak evolution and temperature-corrected micro X-ray diffraction data provides clear observations of solidification and solid state phase transformations under non-equilibrium conditions similar to beam-based additive manufacturing. (C) 2015 Elsevier Ltd. All rights reserved.

Visualizing individual charges confined to molecules and observing their dynamics with high spatial resolution is a challenge for advancing various fields in science, ranging from mesoscopic physics to electron transfer events in biological molecules. We show here, that the high sensitivity of low-energy electrons to local electric fields can be employed to directly visualize individual charged adsorbates and to study their behaviour in a quantitative way. This makes electron holography a unique probing tool for directly visualising charge distributions with a sensitivity of a fraction of an elementary charge. Moreover, spatial resolution in the nanometer range and fast data acquisition inherent to lens-less low-energy electron holography allows for direct visual inspection of charge transfer processes.

It can be expected that many elderly people have impaired opening capacity of food packaging bearing in mind the changes in functionality and physical strength that occur during ageing. This study determined the relation of the quantitative force required to open selected food packaging systems with findings derived from qualitative focus group studies to retrieve comprehensive information on the specific needs of seniors. The focus group studies revealed that the assessment of the ease of opening is very subjective and can vary from objective measurements. The quantitative measurement of the force required to open the ‘easy to open’ thermoformed tray resulted in considerably higher peel initiation forces of 22.50 ± 1.62N compared to the standard tray (12.80 ± 1.93 N). However, the packaging type was still felt to be easier to open because of the enlarged tab and peeling corner, which was said to be easy to grip. Conversely, the stand-up pouches with twist-off caps could only be opened with difficulty because of the small caps and the difficulty in breaking seals, despite the substantially lower opening forces of 0.46 ± 0.06Nm compared with the other torque closures. The evaluation of a package was found to be only partly dependent on the required opening force but strongly influenced by various design factors and consumer’s expectations as well as experiences.

A novel fabrication method was established to produce flexible, transparent, and robust tipless hollow atomic force microscopy (AFM) cantilevers made entirely from SU-8. Channels of 3 μm thickness and several millimeters length were integrated into 12 μm thick and 40 μm wide cantilevers. Connected to a pressure controller, the devices showed high sealing performance with no leakage up to 6 bars. Changing the cantilever lengths from 100 μm to 500 μm among the same wafer allowed the targeting of various spring constants ranging from 0.5 to 80 N m−1 within a single fabrication run. These hollow polymeric AFM cantilevers were operated in the optical beam deflection configuration. To demonstrate the performance of the device, single-cell force spectroscopy experiments were performed with a single probe detaching in a serial protocol more than 100 Saccharomyces cerevisiae yeast cells from plain glass and glass coated with polydopamine while measuring adhesion forces in the sub-nanoNewton range. SU-8 now offers a new alternative to conventional silicon-based hollow cantilevers with more flexibility in terms of complex geometric design and surface chemistry modification.

Ultrathin films of boron nitride (BN) have recently attracted considerable interest given their successful incorporation in graphene nanodevices and their use as spacer layers to electronically decouple and order functional adsorbates. Here, we introduce a BN monolayer grown by chemical vapor deposition of borazine on a single crystal Cu support, representing a model system for an electronically patterned but topographically smooth substrate. Scanning tunneling microscopy and spectroscopy experiments evidence a weak bonding of the single BN sheet to Cu, preserving the insulating character of bulk hexagonal boron nitride, combined with a periodic lateral variation of the local work function and the surface potential. Complementary density functional theory calculations reveal a varying registry of the BN relative to the Cu lattice as origin of this electronic Moiré-like superstructure.

We demonstrate the ability to trap, levitate, and orient single anisometric nanoscale objects with high angular precision in a fluid. An electrostatic fluidic trap confines a spherical object at a spatial location defined by the minimum of the electrostatic system free energy. For an anisometric object and a potential well lacking angular symmetry, the system free energy can further strongly depend on the object's orientation in the trap. Engineering the morphology of the trap thus enables precise spatial and angular confinement of a single levitating nano-object, and the process can be massively parallelized. Since the physics of the trap depends strongly on the surface charge of the object, the method is insensitive to the object's dielectric function. Furthermore, levitation of the assembled objects renders them amenable to individual manipulation using externally applied optical, electrical, or hydrodynamic fields, raising prospects for reconfigurable chip-based nano-object assemblies.

Encapsulated microbubbles (MBs) serve as endovascular agents in a wide range of medical ultrasound applications. The oscillatory response of these agents to ultrasonic excitation is determined by MB size, gas content, viscoelastic shell properties and geometrical constraints. The viscoelastic parameters of the MB capsule vary during an oscillation cycle and change irreversibly upon shell rupture. The latter results in marked stress changes on the endothelium of capillary blood vessels due to altered MB dynamics. Mechanical effects on microvessels are crucial for safety and efficacy in applications such as focused ultrasound-mediated blood--brain barrier (BBB) opening. Since direct in vivo quantification of vascular stresses is currently not achievable, computational modelling has established itself as an alternative. We have developed a novel computational framework combining fluid--structure coupling and interface tracking to model the nonlinear dynamics of an encapsulated MB in constrained environments. This framework is used to investigate the mechanical stresses at the endothelium resulting from MB shell rupture in three microvessel setups of increasing levels of geometric detail. All configurations predict substantial elevation of up to 150 {; ; ; \%}; ; ; for peak wall shear stress upon MB breakup, whereas global peak transmural pressure levels remain unaltered. The presence of red blood cells causes confinement of pressure and shear gradients to the proximity of the MB, and the introduction of endothelial texture creates local modulations of shear stress levels. With regard to safety assessments, the mechanical impact of MB breakup is shown to be more important than taking into account individual red blood cells and endothelial texture. The latter two may prove to be relevant to the actual, complex process of BBB opening induced by MB oscillations.

We show how gold recrystallizes when under the influence of electrochemical potentials. This "cold annealing" occurs without charge transfer reactions and preserves nanoscale structural features. By performing the process on plasmonic nanostructures, grain growth is monitored noninvasively by optical spectroscopy. In this way, the influence from crystal structure on plasmon resonances can be investigated independently. Observed spectral changes are in excellent agreement with analytical models and changes in electron relaxation time and plasma frequency are calculated.

We established an in-plane microfabrication process of polymeric AFM micropipettes that include a microchannel with an aperture at the apex without further processing after wafer scale lithography. The channel was obtained by etching a sacrificial electrochemically plated copper layer. Such sideways fabrication scheme offers the possibility of designing various types of cantilevers with different shapes and lengths within a single wafer, such as a length of 500 µm or being connected by two triangular hollow tips. The probes were operated in optical beam deflection AFM mode. First, force-indentation curves were measured on substrates with different stiffness, and then microbeads were spatially manipulated in a hydrogel showing their reusability in case of clogging. Finally, we succeeded in using such probes to carry out cell-isolation experiments of neurons cultured in vitro (2D layers) and in hydrogels (3D architecture).

Single binding events of nanoparticle-labeled DNA strands were detected as stepwise peak shifts in localized surface plasmon resonance by single particle measurement. We confirmed the number of binding events by observing label particles by scanning electron microscopy. Our simulation based on a multiple multipole program showed that the peak shift is dependent on interparticle gap size and binding position. The experimental peak shift distribution was also reproduced by simulation.

Novel cell culture surfaces grafted with the temperature-responsive polymer poly(N-isopropylacrylamide) (PIPAAm) allow the non-invasive detachment of confluent cell monolayers simply by reducing the temperature. [1,2] The harvested cell sheets are recovered together with their deposited extracellular matrix (ECM) and can be used for tissue reconstruction either by direct transplantation of cell sheets to host tissues or by the creation of three-dimensional structures via the layering of individual cell sheets. In contrast to conventional tissue engineering approaches using biodegradable scaffolds or the injection of isolated cell suspensions, this technique, named cell sheet engineering, allows for reconstruction of cell-dense structures with preservation of the critical cell surface proteins. [2] This method has been successfully applied to various tissue reconstructions, including skin, [3] corneal epithelium, [4] urothelium, [5] periodontal ligament, [6] cardiac muscle, [7] and liver lobules. [8] Furthermore, as this cell sheet-based tissue engineering is now emerging as a promising clinical methodology to reconstruct tissues for transplantation, alternatives to the PIPAAm-grafted dishes are elaborated. Further thermoresponsive polymers have been recently applied for cell sheet recovery. [9‐13] Another approach consists in cell growth onto protein-based gels, and subsequent cell sheet detachment through enzymatic digestion of the substrate. [14,15] Finally, Ito et al. proposed a new method named magnetic force-based cell sheet engineering, where the adhesion of cells labeled with magnetite nanoparticles is tuned by magnetic force. [16] We propose here a new platform for cell sheet engineering, involving electronically addressable polyelectrolyte mono- and multilayered thin films. As polyelectrolytes spontaneously adsorb onto oppositely charged surfaces through electrostatic interactions, monolayer coatings are obtained by a simple dipping process in a dilute aqueous solution of the polymer. In this study, we have used the synthetic polymer RGD-modified poly(L-lysine)-graft-poly(ethylene glycol) (PLL-g-PEG/PEGRGD). This polycation promotes specific interactions with cells through itsa/b-integrin-binding sequence Arg-Gly-Asp (RGD) while preventing non-specific protein adsorption via its unfunctionalized PEG arms. [17,18] Moreover, multilayered polyelectrolyte films can be assembled by alternate dipping of a charged surface into dilute solutions of a polycation and a polyanion. [19] This layer-by-layer coating process is simple and applicable to geometrically complex substrates. Furthermore, multilayered thin films can be functionalized by covalent linking, adsorption or embedding of biomolecules; peptides, [20] proteins, [21‐23] drugs, [24] DNA [25] and other bioactive molecules [26,27] incorporated in polyelectrolyte multilayers have been shown to retain their biological activities. For our study, we have selected the polypeptides poly(L-lysine) (PLL) and poly(L-glutamic acid) (PGA), and the extracellular matrix component hyaluronic acid (HA). Both (PLL/HA) and (PLL/ PGA) polyelectrolyte films have been extensively studied and applied in biomedical studies. [28] Recently, polyelectrolyte mono- and multilayers have been shown to desorb from conducting substrates upon electrochemical polarization of the substrate. [29‐31] Based on these results, we have developed a new technique for harvesting cell sheets consisting of two steps: the growth of cells to confluence onto polyelectrolyte thin films and subsequent detachment under electrochemical control. Osteoblasts and fibroblasts grown onto PLL-g-PEG/ PEG-RGD coated indium tin oxide (ITO) could be detached as a cell sheet after the application of a positive potential. Fibroblasts could also be detached from PLL-PGA-PLL-gPEG/PEG-RGD substrate by electrochemical polarization, demonstrating the potential of electrochemically addressable surfaces for the recovery of cell sheets. Moreover, when grown to confluence on mono- or multilayered films made of (PLL/HA) or (PLL/PGA), osteoblasts, fibroblasts and human COMMUNICATION

SUMMARY The paper is devoted to the further development of the particle transport method for the convection problems with diffusion and reaction. Here, the particle transport method for a convection–reaction problem is combined with an Eulerian finite-element method for diffusion in the framework of the operator-splitting approach. The technique possesses a special spatial adaptivity to resolve solution singularities possible due to convection and reaction terms. A monotone projection technique is used to transfer the solution of the convection–reaction subproblem from a moving set of particles onto a fixed grid to initialize the diffusion subproblem. The proposed approach exhibits good mass conservation and works with structured and unstructured meshes. The performance of the presented algorithm is tested on one- and two-dimensional benchmark problems. The numerical results confirm that the method demonstrates good accuracy for the convection-dominated as well as for convection–diffusion problems. Copyright q 2007 John Wiley & Sons, Ltd.

Congenital or posttraumatic bone deformity may lead to reduced range of motion, joint instability, pain, and osteoarthritis. The conventional joint-preserving therapy for such deformities is corrective osteotomy—the anatomical reduction or realignment of bones with fixation. In this procedure, the bone is cut and its fragments are correctly realigned and stabilized with an implant to secure their position during bone healing. Corrective osteotomy is an elective procedure scheduled in advance, providing sufficient time for careful diagnosis and operation planning. Accordingly, computer-based methods have become very popular for its preoperative planning. These methods can improve precision not only by enabling the surgeon to quantify deformities and to simulate the intervention preoperatively in three dimensions, but also by generating a surgical plan of the required correction. However, generation of complex surgical plans is still a major challenge, requiring sophisticated techniques and profound clinical expertise. In addition to preoperative planning, computer-based approaches can also be used to support surgeons during the course of interventions. In particular, since recent advances in additive manufacturing technology have enabled cost-effective production of patient- and intervention-specific osteotomy instruments, customized interventions can thus be planned for and performed using such instruments. In this chapter, state of the art and future perspectives of computer-assisted deformity-correction surgery of the upper and lower extremities are presented. We elaborate on the benefits and pitfalls of different approaches based on our own experience in treating over 150 patients with three-dimensional preoperative planning and patient-specific instrumentation.

This paper presents a simplistic passive dynamic model that is able to create realistic quadrupedal walking, tölting, and trotting motions. The model is inspired by the bipedal spring loaded inverted pendulum (SLIP) model and consists of a distributed mass on four massless legs. Each of the legs is either in ground contact, retracted for swing, or is ready for touch down with a predefined angle of attack. Different gaits, that is, periodic motions differing in interlimb coordination patterns, are generated by choosing different initial model states. Contact patterns and ground reaction forces (GRFs) evolve solely from these initial conditions. By identifying appropriate system parameters in an optimization framework, the model is able to closely match experimentally recorded vertical GRFs of walking and trotting of Warmblood horses, and of tölting of Icelandic horses. In a detailed study, we investigated the sensitivity of the obtained solutions with respect to all states and parameters and quantified the improvement in fitting GRF by including an additional head and neck segment. Our work suggests that quadrupedal gaits are merely different dynamic modes of the same structural system and that we can interpret different gaits as different nonlinear elastic oscillations that propel an animal forward.

Computational Mechanics, 56 (5), ISSN:0178-7675, ISSN:1432-0924

Multifunctional hybrid porous micro-/nanocomposite materials with hierarchical structures of soft silicone nanofilaments on hard porous glass microbeads are designed and synthesized. Such materials display selective super-antiwetting/superwetting properties with unique mechanical, chemical, and thermal stabilities, as well as excellent antifouling properties. They are ideal materials for highly efficient separation of oil/water mixtures and emulsions, and display great advantages as carriers for organocatalysts.

We probe the local detection efficiency in a nanowire superconducting single-photon detector along the cross-section of the wire with a far subwavelength resolution. We experimentally find a strong variation in the local detection efficiency of the device. We demonstrate that this effect explains previously observed variations in NbN detector efficiency as a function of device geometry.

For the control of unmanned aerial vehicles (UAVs) in GPS-denied environments, cameras have been widely exploited as the main sensory modality for addressing the UAV state estimation problem. However, the use of visual information for ego-motion estimation presents several theoretical and practical difficulties, such as data association, occlusions, and lack of direct metric information when exploiting monocular cameras. In this paper, we address these issues by considering a quadrotor UAV equipped with an onboard monocular camera and an inertial measurement unit (IMU). First, we propose a robust ego-motion estimation algorithm for recovering the UAV scaled linear velocity and angular velocity from optical flow by exploiting the so-called continuous homography constraint in the presence of planar scenes. Then, we address the problem of retrieving the (unknown) metric scale by fusing the visual information with measurements from the onboard IMU. To this end, two different estimation strategies are proposed and critically compared: a first exploiting the classical extended Kalman filter (EKF) formulation, and a second one based on a novel nonlinear estimation framework. The main advantage of the latter scheme lies in the possibility of imposing a desired transient response to the estimation error when the camera moves with a constant acceleration norm with respect to the observed plane. We indeed show that, when compared against the EKF on the same trajectory and sensory data, the nonlinear scheme yields considerably superior performance in terms of convergence rate and predictability of the estimation. The paper is then concluded by an extensive experimental validation, including an onboard closed-loop control of a real quadrotor UAV meant to demonstrate the robustness of our approach in real-world conditions.

Besides active, functional molecular building blocks such as diodes or switches, passive components as, e.g., molecular wires, are required to realize molecular-scale electronics. Incorporating metal centers in the molecular backbone enables the molecular energy levels to be tuned in respect to the Fermi energy of the electrodes. Furthermore, by using more than one metal center and sp-bridging ligands, a strongly delocalized electron system is formed between these metallic "dopants", facilitating transport along the molecular backbone. Here, we study the influence of molecule--metal coupling on charge transport of dinuclear X(PP)$_2$FeC$_4$Fe(PP)$_2$X molecular wires (PP = Et$_2$PCH$_2$CH$_2$PEt$_2$); X = CN (1), NCS (2), NCSe (3), C$_4$SnMe$_3$ (4) and C$_2$SnMe$_3$ (5)) under ultra-high vacuum and variable temperature conditions. In contrast to 1 which showed unstable junctions at very low conductance ($8.1\cdot10^{-7}$ G$_0$), 4 formed a Au-C$_4$FeC$_4$FeC$_4$-Au junction 4' after SnMe$_3$ extrusion which revealed a conductance of $8.9\cdot10^{-3}$ G$_0$, three orders of magnitude higher than for 2 ($7.9\cdot10^{-6}$ G$_0$) and two orders of magnitude higher than for 3 ($3.8\cdot10^{-4}$ G$_0$). Density functional theory (DFT) confirmed the experimental trend in the conductance for the various anchoring motifs. The strong hybridization of molecular and metal states found in the C--Au coupling case enables the delocalized electronic system of the organometallic Fe$_2$ backbone to be extended over the molecule-metal interfaces to the metal electrodes to establish high-conductive molecular wires.

Foam bitumen is highly efficient in wetting and coating the surface of mineral aggregate at lower temperature. In order to improve understanding and characterization of the bitumen foam, X-ray radiography was used to study the formation and decay of bitumen foam in 2D representation. Image segmentation analysis was used to determine the foam bubble size distribution. In addition, the main parameters influencing foam bitumen formation, water content, and temperature were also investigated. The results demonstrate the influence of the water content on morphology and expansion of foam bitumen bubbles. Adding more water in the foaming process leads to quick collapse of bubbles and intensifies coalescence of foam bitumen. Higher temperatures produces larger bubbles at early foaming stage compared to lower temperature. Moreover the morphology of bubble formation depends on the types of bitumen used. An exponential function has been implemented to represent the bubble area distribution.