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- ItemGlycosaminoglycan-based hydrogels to modulate heterocellular communication in in vitro angiogenesis models(London : Nature Publishing Group, 2014) Chwalek, K.; Tsurkan, M.V.; Freudenberg, U.; Werner, C.Angiogenesis, the outgrowth of blood vessels, is crucial in development, disease and regeneration. Studying angiogenesis in vitro remains challenging because the capillary morphogenesis of endothelial cells (ECs) is controlled by multiple exogenous signals. Therefore, a set of in situ-forming starPEG-heparin hydrogels was used to identify matrix parameters and cellular interactions that best support EC morphogenesis. We showed that a particular type of soft, matrix metalloproteinase-degradable hydrogel containing covalently bound integrin ligands and reversibly conjugated pro-angiogenic growth factors could boost the development of highly branched, interconnected, and lumenized endothelial capillary networks. Using these effective matrix conditions, 3D heterocellular interactions of ECs with different mural cells were demonstrated that enabled EC network modulation and maintenance of stable vascular capillaries over periods of about one month in vitro. The approach was also shown to permit in vitro tumor vascularization experiments with unprecedented levels of control over both ECs and tumor cells. In total, the introduced 3D hydrogel co-culture system could offer unique options for dissecting and adjusting biochemical, biophysical, and cell-cell triggers in tissue-related vascularization models.
- ItemFree-standing Fe2O3 nanomembranes enabling ultra-long cycling life and high rate capability for Li-ion batteries(London : Nature Publishing Group, 2014) Liu, X.; Si, W.; Zhang, J.; Sun, X.; Deng, J.; Baunack, S.; Oswald, S.; Liu, L.; Yan, C.; Schmidt, O.G.With Fe2O3 as a proof-of-concept, free-standing nanomembrane structure is demonstrated to be highly advantageous to improve the performance of Li-ion batteries. The Fe2O3 nanomembrane electrodes exhibit ultra-long cycling life at high current rates with satisfactory capacity (808 mAh g-1 after 1000 cycles at 2 C and 530 mAh g-1 after 3000 cycles at 6 C) as well as repeatable high rate capability up to 50 C. The excellent performance benefits particularly from the unique structural advantages of the nanomembranes. The mechanical feature can buffer the strain of lithiation/delithiation to postpone the pulverization. The two-dimensional transport pathways in between the nanomembranes can promote the pseudo-capacitive type storage. The parallel-laid nanomembranes, which are coated by polymeric gel-like film and SEI layer with the electrolyte in between layers, electrochemically behave like numerous "mini-capacitors" to provide the pseudo-capacitance thus maintain the capacity at high rate.
- ItemRobustness of interrelated traffic networks to cascading failures(London : Nature Publishing Group, 2014) Su, Z.; Li, L.; Peng, H.; Kurths, J.; Xiao, J.; Yang, Y.The vulnerability to real-life networks against small initial attacks has been one of outstanding challenges in the study of interrelated networks. We study cascading failures in two interrelated networks S and B composed from dependency chains and connectivity links respectively. This work proposes a realistic model for cascading failures based on the redistribution of traffic flow. We study the Barabási-Albert networks (BA) and Erd's-Rényi graphs (ER) with such structure, and found that the efficiency sharply decreases with increasing percentages of the dependency nodes for removing a node randomly. Furthermore, we study the robustness of interrelated traffic networks, especially the subway and bus network in Beijing. By analyzing different attacking strategies, we uncover that the efficiency of the city traffic system has a non-equilibrium phase transition at low capacity of the networks. This explains why the pressure of the traffic overload is relaxed by singly increasing the number of small buses during rush hours. We also found that the increment of some buses may release traffic jam caused by removing a node of the bus network randomly if the damage is limited. However, the efficiencies to transfer people flow will sharper increase when the capacity of the subway network αS > α0.
- ItemSpatiooral coherence mapping of few-cycle vortex pulses(London : Nature Publishing Group, 2014) Grunwald, R.; Elsaesser, T.; Bock, M.Light carrying an orbital angular momentum (OAM) displays an optical phase front rotating in space and time and a vanishing intensity, a so-called vortex, in the center. Beyond continuous-wave vortex beams, optical pulses with a finite OAM are important for many areas of science and technology, ranging from the selective manipulation and excitation of matter to telecommunications. Generation of vortex pulses with a duration of few optical cycles requires new methods for characterising their coherence properties in space and time. Here we report a novel approach for flexibly shaping and characterising few-cycle vortex pulses of tunable topological charge with two sequentially arranged spatial light modulators. The reconfigurable optical arrangement combines interferometry, wavefront sensing, time-of-flight and nonlinear correlation techniques in a very compact setup, providing complete spatiooral coherence maps at minimum pulse distortions. Sub-7â €...fs pulses carrying different optical angular momenta are generated in single and multichannel geometries and characterised in comparison to zero-order Laguerre-Gaussian beams. To the best of our knowledge, this represents the shortest pulse durations reported for direct vortex shaping and detection with spatial light modulators. This access to space-time coupling effects with sub-femtosecond time resolution opens new prospects for tailored twisted light transients of extremely short duration.
- ItemLow-dimensional behavior of Kuramoto model with inertia in complex networks(London : Nature Publishing Group, 2014) Ji, P.; Peron, T.K.D.M.; Rodrigues, F.A.; Kurths, J.Low-dimensional behavior of large systems of globally coupled oscillators has been intensively investigated since the introduction of the Ott-Antonsen ansatz. In this report, we generalize the Ott-Antonsen ansatz to second-order Kuramoto models in complex networks. With an additional inertia term, we find a low-dimensional behavior similar to the first-order Kuramoto model, derive a self-consistent equation and seek the time-dependent derivation of the order parameter. Numerical simulations are also conducted to verify our analytical results.
- ItemWavelength-versatile graphene-gold film saturable absorber mirror for ultra-broadband mode-locking of bulk lasers(London : Nature Publishing Group, 2014) Ma, J.; Xie, G.; Lv, P.; Gao, W.; Yuan, P.; Qian, L.; Griebner, U.; Petrov, V.; Yu, H.; Zhang, H.; Wang, J.An ultra-broadband graphene-gold film saturable absorber mirror (GG-SAM) with a spectral coverage exceeding 1300 nm is experimentally demonstrated for mode-locking of bulk solid-state lasers. Owing to the p-type doping effect caused by graphene-gold film interaction, the graphene on gold-film substrate shows a remarkably lower light absorption relative to pristine graphene, which is very helpful to achieve continuous-wave mode-locking in low-gain bulk lasers. Using the GG-SAM sample, stable mode-locking is realized in a Yb:YCOB bulk laser near 1 μm, a Tm:CLNGG bulk laser near 2 μm and a Cr:ZnSe bulk laser near 2.4 μm. The saturable absorption is characterised at an intermediate wavelength of 1.56 μm by pump-probe measurements. The as-fabricated GG-SAM with ultra-broad bandwidth, ultrafast recovery time, low absorption, and low cost has great potential as a universal saturable absorber mirror for mode-locking of various bulk lasers with unprecedented spectral coverage.
- ItemSynchronization in output-coupled temporal Boolean networks(London : Nature Publishing Group, 2014) Lu, J.; Zhong, J.; Tang, Y.; Huang, T.; Cao, J.; Kurths, J.This paper presents an analytical study of synchronization in an array of output-coupled temporal Boolean networks. A temporal Boolean network (TBN) is a logical dynamic system developed to model Boolean networks with regulatory delays. Both state delay and output delay are considered, and these two delays are assumed to be different. By referring to the algebraic representations of logical dynamics and using the semi-tensor product of matrices, the output-coupled TBNs are firstly converted into a discrete-time algebraic evolution system, and then the relationship between the states of coupled TBNs and the initial state sequence is obtained. Then, some necessary and sufficient conditions are derived for the synchronization of an array of TBNs with an arbitrary given initial state sequence. Two numerical examples including one epigenetic model are finally given to illustrate the obtained results.
- ItemPlasmon-driven sequential chemical reactions in an aqueous environment(London : Nature Publishing Group, 2014) Zhang, X.; Wang, P.; Zhang, Z.; Fang, Y.; Sun, M.Plasmon-driven sequential chemical reactions were successfully realized in an aqueous environment. In an electrochemical environment, sequential chemical reactions were driven by an applied potential and laser irradiation. Furthermore, the rate of the chemical reaction was controlled via pH, which provides indirect evidence that the hot electrons generated from plasmon decay play an important role in plasmon-driven chemical reactions. In acidic conditions, the hot electrons were captured by the abundant H + in the aqueous environment, which prevented the chemical reaction. The developed plasmon-driven chemical reactions in an aqueous environment will significantly expand the applications of plasmon chemistry and may provide a promising avenue for green chemistry using plasmon catalysis in aqueous environments under irradiation by sunlight.
- ItemPlasmon-driven dimerization via S-S chemical bond in an aqueous environment(London : Nature Publishing Group, 2014) Cui, L.; Wang, P.; Chen, X.; Fang, Y.; Zhang, Z.; Sun, M.The surface-enhanced Raman scattering (SERS) spectra of thioanisole are experimentally investigated in an electrochemical environment in this study. Two Raman peaks, which depend strongly not only on electric potential but also on the local surface plasmon resonances (LSPR), have been observed. Theoretical calculations reveal that thioanisole is first dissociated from thiophenol via the S-CH3 bond; plasmons then drive the dimerisation of thiophenol via the S-S bond, which is strongly potential dependent. One Raman peak corresponds to the S-S vibrational mode of the thiophenol dimer, and the other corresponds to the asymmetric C-C stretching modes of the benzenyl of the thiophenol dimer. The potential-dependent two Raman modes is the potential-dependent dimerisation dynamics of thiophenol via the S-S bond. Our experimental findings provide insight into the structural elucidation of adsorbed molecules and molecular surface reaction dynamics.
- ItemUltrafast high-resolution mass spectrometric finger pore imaging in latent finger prints(London : Nature Publishing Group, 2014) Elsner, C.; Abel, B.Latent finger prints (LFPs) are deposits of sweat components in ridge and groove patterns, left after human fingers contact with a surface. Being important targets in biometry and forensic investigations they contain more information than topological patterns. With laser desorption mass spectrometry imaging (LD-MSI) we record 'three-dimensional' finger prints with additional chemical information as the third dimension. Here we show the potential of fast finger pore imaging (FPI) in latent finger prints employing LD-MSI without a classical matrix in a high-spatial resolution mode. Thin films of gold rapidly sputtered on top of the sample are used for desorption. FPI employing an optical image for rapid spatial orientation and guiding of the desorption laser enables the rapid analysis of individual finger pores, and the chemical composition of their excretions. With this approach we rapidly detect metabolites, drugs, and characteristic excretions from the inside of the human organism by a minimally-invasive strategy, and distinguish them from chemicals in contact with fingers without any labeling. The fast finger pore imaging, analysis, and screening approach opens the door for a vast number of novel applications in such different fields as forensics, doping and medication control, therapy, as well as rapid profiling of individuals.