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- Item4D Biofabrication of fibrous artificial nerve graft for neuron regeneration(Bristol : IOP Publ., 2020) Apsite, Indra; Constante, Gissela; Dulle, Martin; Vogt, Lena; Caspari, Anja; Boccaccini, Aldo R.; Synytska, Alla; Salehi, Sahar; Ionov, LeonidIn this paper, we describe the application of the 4D biofabrication approach for the fabrication of artificial nerve graft. Bilayer scaffolds consisting of uniaxially aligned polycaprolactone-poly(glycerol sebacate) (PCL-PGS) and randomly aligned methacrylated hyaluronic acid (HA-MA) fibers were fabricated using electrospinning and further used for the culture of PC-12 neuron cells. Tubular structures form instantly after immersion of fibrous bilayer in an aqueous buffer and the diameter of obtained tubes can be controlled by changing bilayer parameters such as the thickness of each layer, overall bilayer thickness, and medium counterion concentration. Designed scaffolds showed a self-folded scroll-like structure with high stability after four weeks of real-time degradation. The significance of this research is in the fabrication of tuneable tubular nerve guide conduits that can simplify the current existing clinical treatment of neural injuries. © 2020 The Author(s). Published by IOP Publishing Ltd.
- ItemMWCNT induced negative real permittivity in a copolyester of Bisphenol-A with terephthalic and isophthalic acids(Bristol : IOP Publ., 2020) Özdemir, Zeynep Güven; Daşdan, Dolunay Şakar; Kavak, Pelin; Pionteck, Jürgen; Pötschke, Petra; Voit, Brigitte; SüngüMısırlıoğlu, BanuIn the present study, the negative real permittivity behavior of a copolyester of bisphenol-A with terephthalic acid and isophthalic acid (PAr) containing 1.5 to 7.5 wt% multi-walled carbon nanotubes (MWCNTs) have been investigated in detail. The structural and morphological analysis of the melt-mixed composites was performed by Fourier transform infrared spectroscopy using attenuated total reflection (FTIR-ATR), atomic force microscopy (AFM), X-ray diffraction (XRD), and light microscopy. The influences of the MWCNT filler on the AC impedance, complex permittivity, and AC conductivity of the PAr polymer matrix were investigated at different operating temperatures varied between 296 K and 373 K. The transition from a negative to positive real permittivity was observed at different crossover frequencies depending on the MWCNT content of the composites whereas pure PAr showed positive values at all frequencies. The negative real permittivity characteristic of the composites was discussed in the context of Drude model. © 2020 The Author(s). Published by IOP Publishing Ltd.
- ItemElastic properties of single crystal Bi12SiO20 as a function of pressure and temperature and acoustic attenuation effects in Bi12 MO20 (M = Si, Ge and Ti)(Bristol : IOP Publ., 2020) Haussühl, Eiken; Reichmann, Hans Josef; Schreuer, Jürgen; Friedrich, Alexandra; Hirschle, Christian; Bayarjargal, Lkhamsuren; Winkler, Björn; Alencar, Igor; Wiehl, Leonore; Ganschow, SteffenA comprehensive study of sillenite Bi12SiO20 single-crystal properties, including elastic stiffness and piezoelectric coefficients, dielectric permittivity, thermal expansion and molar heat capacity, is presented. Brillouin-interferometry measurements (up to 27 GPa), which were performed at high pressures for the first time, and ab initio calculations based on density functional theory (up to 50 GPa) show the stability of the sillenite structure in the investigated pressure range, in agreement with previous studies. Elastic stiffness coefficients c 11 and c 12 are found to increase continuously with pressure while c 44 increases slightly for lower pressures and remains nearly constant above 15 GPa. Heat-capacity measurements were performed with a quasi-adiabatic calorimeter employing the relaxation method between 2 K and 395 K. No phase transition could be observed in this temperature interval. Standard molar entropy, enthalpy change and Debye temperature are extracted from the data. The results are found to be roughly half of the previous values reported in the literature. The discrepancy is attributed to the overestimation of the Debye temperature which was extracted from high-temperature data. Additionally, Debye temperatures obtained from mean sound velocities derived by Voigt-Reuss averaging are in agreement with our heat-capacity results. Finally, a complete set of electromechanical coefficients was deduced from the application of resonant ultrasound spectroscopy between 103 K and 733 K. No discontinuities in the temperature dependence of the coefficients are observed. High-temperature (up to 1100 K) resonant ultrasound spectra recorded for Bi12 MO20 crystals revealed strong and reversible acoustic dissipation effects at 870 K, 960 K and 550 K for M = Si, Ge and Ti, respectively. Resonances with small contributions from the elastic shear stiffness c 44 and the piezoelectric stress coefficient e 123 are almost unaffected by this dissipation. © 2020 The Author(s). Published by IOP Publishing Ltd.
- ItemDelayed relaxation of highly excited naphthalene cations(Bristol : IOP Publ., 2020) Reitsma, G.; Hummert, J.; Dura, J.; Loriot, V.; Vrakking, M.J.J.; Lépine, F.; Kornilov, O.The efficiency of energy transfer in ultrafast electronic relaxation of molecules depends strongly on the complex interplay between electronic and nuclear motion. In this study we use wavelength-selected XUV pulses to induce relaxation dynamics of highly excited cationic states of naphthalene. Surprisingly, the observed relaxation lifetimes increase with the cationic excitation energy. We propose that this is a manifestation of a quantum mechanical population trapping that leads to delayed relaxation of molecules in the regions with a high density of excited states. © 2019 Published under licence by IOP Publishing Ltd.
- ItemStrong-Field Ionization of Linear Molecules by a Bichromatic Elliptically Polarized Laser Field with Coplanar Counterrotating or Corotating Components of Different Frequencies(Bristol : IOP Publ., 2020) Gazibegović-Busuladžić, A.; Busuladžić, M.; Čerkić, A.; Hasović, E.; Becker, W.; Milošević, D.B.We investigate strong-field ionization of linear molecules by a two-color laser field of frequencies rω and sω having coplanar counterrotating or corotating elliptically polarized components (ω is the fundamental laser field frequency and r and s are integers). Using the improved molecular strong-field approximation we analyze direct above-threshold ionization (ATI) and high-order ATI (HATI) spectra. More precisely, reflection and rotational symmetries of these spectra for linear molecules aligned in the laser-field polarization plane are considered. The reflection symmetries for particular molecular orientations, known to be valid for a bicircular field (this is the field with circularly polarized counterrotating components), are valid also for arbitrary component ellipticities. However, specific rotational symmetries that are satisfied for HATI by a bicircular field, are violated for an arbitrary elliptically polarized field with counterrotating components. For the corotating case and the N2 molecule we analyze molecular-orientation-dependent interferences and plateau structures for various ellipticities.
- ItemOccurrence of Flux Jumps in MgB2 Bulk Magnets during Pulse-Field Magnetization(Bristol : IOP Publ., 2020) Sakai, N.; Oka, T.; Yamanaka, K.; Dadiel, L.; Oki, H.; Ogawa, J.; Fukui, S.; Scheiter, J.; Häßler, W.; Yokoyama, K; Noudem, J.; Miryala, M.; Murakami, M.The magnetic flux capturing of MgB2 bulk magnets made by spark plasma sintering process has been precisely investigated to clarify the mechanism of flux motions during the pulse-field magnetization processes. The field trapping ratio B T/B P was evaluated as a key parameter of field trapping ability which strongly relates to the heat generation due to the rapid flux motion in the samples. The time dependence of magnetic flux density revealed the actual flux motion which penetrated the samples. The trapped fields B T and field trapping ratios B T/B P of various samples were classified into three regions of 'no flux flow', 'fast flux flow' and 'flux jump' according to the generation of heat and its propagation. A flux jump was observed late at 280 ms from the beginning of PFM process, while the field penetration B P showed its peak at 10 ms. Considering the heat propagation speed, the long-delayed flux jump should be attributed to the macroscopic barriers against the heat propagation to the surface centre of bulk magnet. © Published under licence by IOP Publishing Ltd.
- ItemCorrelations between the structure and superconducting properties of MT-YBaCuO(Bristol : IOP Publ., 2020) Prikhna, T.A.; Moshchill, V.E.; Rabier, J.; Chaud, X.; Joulain, A.; Pan, A.V.; Litskendorf, D.; Habisreuther, T.Comprehensive experimental results of fully oxidized (up to YBa2Cu3O6,9-7) melt-Textured YBaCuO materials with different microstructures are presented. These microstructures are built respectively: (1) with a high dislocations density but almost without twins (after high temperature treatment at 2 GPa) and (2) with a high twin density, but practically free from dislocations and stacking faults (after high temperature oxygenation at 10-16 MPa). It is shown that for attaining high critical current densities and fields of irreversibility (jc(H-c, 0 T)=9•104 A/cm2, H irr=9.7 T at 77 K), a high twin density in YBa2Cu3O6.9-7 matrix of MT-YBCO is required. The density of twins in fully oxidized materials depends on the distances between Y2BaCuO5 inclusions, larger twin densities are related to shorter distances between inclusions. The influence of phase composition of the initial powder mixtures on the distances between Y2BaCuO5 inclusions have been characterized and discussed. © Published under licence by IOP Publishing Ltd.
- ItemGeneration of elliptically polarized soft x rays using high-order harmonic generation with orthogonal two-color laser fields(Bristol : IOP Publ., 2020) Milošević, D.B.; Becker, W.High-order harmonic generation by orthogonally polarized two-color (OTC) laser fields is analysed using strong-field approximation and quantum-orbit theory. Results for the field components frequency ratio of 2:1 and 3:1 are presented and compared. We have shown that, depending on the relative phase between the field components, the shape of the high-harmonic spectrum can be very different from that obtained by a monochromatic linearly polarized laser field. It is also shown that it is possible to generate elliptically polarized high-order harmonics with very high photon energies using OTC laser field with the frequency ratio of 3:1 and a long fundamental wavelength. An effective relative phase control of the harmonic emission is demonstrated. The obtained results are explained using the quantum-orbit theory. © Published under licence by IOP Publishing Ltd.
- ItemMagnetic Flux Trapping and Flux Jumps in Pulsed Field Magnetizing Processes in REBCO and Mg-B Bulk Magnets(Bristol : IOP Publ., 2020) Oka, T.; Takeda, A.; Oki, H.; Yamanaka, K.; Dadiel, L.; Yokoyama, K.; Häßler, W.; Scheiter, J.; Sakai, N.; Murakami, M.Pulsed-field magnetization technique (PFM) is expected as a cheap and an easy way for HTS bulk materials for utilizing as intense magnets. As the generation of heat due to magnetic flux motion in bulk magnets causes serious degradation of captured fields, it is important to investigate the flux motions during PFM in various field applications. The authors precisely measured the magnetic flux motion in the cryocooled MgB2 bulk magnets containing various amount of Ti. We classified the motions to "no flux flow (NFF)", "fast flux flow (FFF)", and "flux jump (FJ)" regions. The results showed that addition of Ti shifts the field invasion area to high field areas, and expands the NFF regions. The highest field-trapping appears at the upper end of the NFF region. Since the heat generation and its propagation should attribute to the dissipation of magnetic flux, FFF leads to FJ. Compared with MgB2, we referred to GdBCO as for the flux motion. A flux jump was observed at 30 K when the pulse field of 7 T was applied to the preactivated sample, showing its stability against FJ. © Published under licence by IOP Publishing Ltd.
- ItemA review on stretchable magnetic field sensorics(Bristol : IOP Publ., 2020) Melzer, M.; Makarov, D.; Schmidt, O.G.The current establishment of stretchable electronics to form a seamless link between soft or even living materials and the digital world is at the forefront of multidisciplinary research efforts, bridging physics, engineering and materials science. Magnetic functionalities can provide a sense of displacement, orientation or proximity to this novel formulation of electronics. This work reviews the recent development of stretchable magnetic field sensorics relying on the combination of metallic thin films revealing a giant magnetoresistance effect with elastomeric materials. Stretchability of the magnetic nanomembranes is achieved by specific morphologic features (e.g. wrinkles or microcracks), which accommodate the applied tensile deformation while maintaining the electrical and magnetic integrity of the sensor device. The entire development, from the demonstration of the world's first elastically stretchable magnetic sensor to the realization of a technology platform for robust, ready-to-use elastic magnetosensorics is described. Soft giant magnetoresistive elements exhibiting the same sensing performance as on conventional rigid supports, but with fully strain invariant properties up to 270% stretching have been demonstrated. With their unique mechanical properties, these sensor elements readily conform to ubiquitous objects of arbitrary shapes including the human skin. Stretchable magnetoelectronic sensors can equip soft and epidermal electronic systems with navigation, orientation, motion tracking and touchless control capabilities. A variety of novel technologies, like electronic skins, smart textiles, soft robotics and actuators, active medical implants and soft consumer electronics will benefit from these new magnetic functionalities. © 2019 IOP Publishing Ltd.