Table of contents

The importance of curvature as a structural feature of biological membranes has been recognized for many years and has fascinated scientists from a wide range of different backgrounds. On the one hand, changes in membrane morphology are involved in a plethora of phenomena involving the plasma membrane of eukaryotic cells, including endo- and exocytosis, phagocytosis and filopodia formation. On the other hand, a multitude of intracellular processes at the level of organelles rely on generation, modulation, and maintenance of membrane curvature to maintain the organelle shape and functionality. The contribution of biophysicists and biologists is essential for shedding light on the mechanistic understanding and quantification of these processes.

Given the vast complexity of phenomena and mechanisms involved in the coupling between membrane shape and function, it is not always clear in what direction to advance to eventually arrive at an exhaustive understanding of this important research area. The 2018 Biomembrane Curvature and Remodeling Roadmap of Journal of Physics D: Applied Physics addresses this need for clarity and is intended to provide guidance both for students who have just entered the field as well as established scientists who would like to improve their orientation within this fascinating area.

The clade of Myxogastria, commonly described as true or plasmodial slime molds, contains more than 1000 species. During their life cycle many of these slime molds develop extended networks of connected veins, known as unicellular (phanero)plasmodia. Among those, Physarum polycephalum gathered by far the most attention of biologists and physicists. Via oscillating cytoplasmic streams nutrients as well as signaling factors spread through the adaptive plasmodial network. These properties have rendered it not only a model organism for acellular slime molds, but also a model to investigate network dynamics, biological fluid-dynamics and food foraging behavior. Here, we studied parameters of plasmodial growth and network development, including chemotactic responses, in three slime mold species: Physarum polycephalum, Badhamia utricularis, and Fuligo septica. We discovered significant variations in chemotaxis, velocity, and oscillatory behavior of plasmodia among and within these species. Interestingly the patterns of the variations also reflect phylogenetic relationships of the species. In contrast to a common notion, phaneroplasmodia of slime molds develop diverse and specifically organized networks by triggers yet to be explored. This work lays the ground for studying more of these organisms to understand basic features of planar network organization and their variations, which evolved as successful solutions of nature.

The properties of a magnonic crystal are expected to be strongly influenced by the presence of a thermal gradient. We investigated the propagation of backward volume and surface magnetostatic spin-waves in a 1D magnonic crystal (MC) exposed to a continuous spatial temperature gradient. It is shown that the thermal gradient applied along the propagation direction leads to a frequency shift and a modification of the transmission characteristics of the spin-waves. The frequency shift is caused by a variation in saturation magnetization due to the change in absolute temperature. The altered transmission manifests itself in a broadening of MC band gaps and the corresponding narrowing of the MC passbands and is understood to be a result of a spatial transformation of the spin-waves wavelengths in a thermal gradient. Furthermore, the transmission characteristics of spin-waves in a thermal gradient have been verified by numerical calculations based on the approach of the transmission matrix. The results of the calculations demonstrate a good agreement with the experimentally measured data.

Biologically plausible neuromorphic computing systems are attracting considerable attention due to their low latency, massively parallel information processing abilities, and their high energy efficiency. To achieve these features neuromorphic silicon neuron circuits need to be integrated with plastic synapse circuits capable of on-line learning and storage of synaptic weights. Within this context, memristive devices play a key role thanks to their non-volatility, scalability, and compatibility with the complementary metal–oxide–semiconductor fabrication process. However, neuro-memristive systems are still facing difficult challenges for implementing efficient learning protocols. Here, we propose and demonstrate in hardware a spike-driven threshold-based learning rule which goes beyond conventional spike-timing dependent plasticity mechanisms, by also taking into account the neuron membrane potential and its firing rate. The mixed memristive–neuromorphic system we demonstrate comprises an oxide-based memristive synapse device placed between two silicon neurons implemented on a neuromorphic chip that comprises the proper interfacing and spike-based learning circuits designed to drive the memristive elements. We show how the system is able to emulate in real-time weight dependent post-synaptic activity and drive synaptic weight updates at the memristive synapse level following the spike-driven learning rule presented. We validate this spike-based learning mechanism with experimental results and quantify the system performance with basic learning experiments.

Optically-driven terahertz (THz) modulation generally requires excitation of excessively large photoconductivity of active components, which poses huge challenges for realization and practical applications. With the aid of an analytical circuit model, we demonstrate an approach to alleviate the trade-off between large amplitude modulation and use of low photoconductivity in complementary split-ring resonator modulators. As revealed by analytical results and verified by full-wave simulation, the maximum modulation depth and needed photoconductivity are determined by the inductance and gap resistance of the structure, respectively. Therefore, by tailoring its inductance and resistance via geometry adjustment, both improvement of modulation efficiency and reduction of photoconductivity are simultaneously realized. A large amplitude modulation ~0.5 is achieved with an ultralow conductivity of 2000 S m⁻¹. The proposed approach might offer a guideline for structure design of THz devices with various active components.

This paper reports on the studies of current collapse phenomenon induced by surface trapped charges during gate pulse switching in AlGaN/GaN heterostructure high-electron-mobility transistors. A physical-based model, taking into account the distribution features of the applied electric field along the surface of the device barrier layer near the drain-side gate corner, is proposed to analyse the electron trapping and de-trapping processes at the ionized donor-like traps during the device off-state or on-state process. Then the model is analysed and verified by TCAD simulation and laboratory measurement data. The morphology of the current collapse related AlGaN surface is investigated by SEM and AFM characterizations. The dynamic process and quantitative relationship between the electric field and trapped electron density are determined and analysed in detail. The spatial distributions of the trapped electrons and excess free electrons along AlGaN barrier surface are achieved by using the proposed physical model. The work provides a distinct perspective to understand and quantify the current collapse mechanism in AlGaN/GaN power devices, and it can also assist engineers for a better device design.

This paper focuses on the multi-dimensional simulation of non-equilibrium plasma generated by nanosecond pulsed discharge in air, at pressure values higher than atmospheric. Voltage profiles and electrode geometry closely match those from a complementary experimental study. Simulations highlight the transition between different post-discharge plasma regimes at increasing pressure and tie the characteristics of the streamers to the electric field distribution in the gap between the electrodes. Results from simulations match experimental observations and qualitatively capture the experimental trend in terms of regime transition pressure and structure of the streamers. As a result, this paper validates a numerical tool that captures the physical and chemical properties of the low-temperature plasma and contributes to expand the understanding of low-temperature plasma ignition processes.

The energy efficient excitation of CO₂ in atmospheric pressure plasmas may be a method to generate solar fuels from renewable energies. This energy efficiency can be very high, if only specific states of the molecules in the plasma are populated creating a strong non-equilibrium. This requires a specific design of the plasma source, method of plasma excitation and choice of gases and admixtures. In this paper, non-equilibrium excitation and dissociation of CO₂ in an atmospheric pressure helium RF plasma jet is analysed for varying absorbed plasma power and admixture levels of CO₂. The concentrations of CO₂ and of CO, as well as the vibrational and rotational temperatures of the possible degrees of freedom of the molecules are evaluated by Fourier transform infrared spectroscopy (FTIR). The molecular rotational vibrational spectra are modelled based on Maxwell–Boltzmann state populations using individual temperatures for each degree of freedom. A strong non-equilibrium excitation of CO₂ and CO has been found. Whereas the rotational temperatures are 400 K or below, the vibrational temperature for CO reaches values up to 1600 K and that of the asymmetric vibration of CO₂ of 700 K. The dependence of these excitation temperatures on plasma power and admixture level is rather weak. The mass balance, the energy and conversion efficiency are consistent with a very simple chemistry model that is dominated by CO₂ dissociation via Penning collisions with helium metastables. A conversion efficiency up to 30% and an energy efficiency up to 10% is observed in the parameter range of the experiment.

By using the conventional Shack–Hartmann sensors, it has been impossible to measure the two-dimensional electron density distributions over the -gas-blast decaying arcs exposed to the strong turbulent flow with high spatial frequency variations in the gas density. In order to remove the high spatial frequency components, spatial filters were implemented into the Shack–Hartmann sensors. The novel sensing system was successfully applied to the decaying arc plasmas under current-zero phases generated in a 50 mm-long interelectrode gap confined by a gas flow nozzle. Our experimental results showed that the decaying arcs had large shot-to-shot variations in the electron densities and arc diameters, and these parameters were not always smallest in the upstream nozzle region with the highest blasting gas speed. Such irreproducible arc behaviour was quite different from the previously reported air and arc plasmas and it was predominantly caused by the spatiotemporally irreproducible strong turbulent flow.

Two of the key questions in plasma medicine are how deep the reactive oxygen and nitrogen species (RONS) generated by a plasma can penetrate into tissue and how the liquid (extracellular and intracellular fluid) composition affects the concentration of RONS. In this paper, different thicknesses of pig muscle tissue are used as a tissue mode to investigate the effect of tissue thickness on the penetration of RONS through tissue. Six different types of liquid (inorganic group: double-distilled water (DDW), 1% phosphate-buffered saline, 0.9% NaCl; organic group: 5% glucose, 2% serum and 10% serum solution) are used in the receiving chamber under the tissue in order to try to understand the effect of liquid composition on the penetration of RONS (H₂O₂, and ) generated by the plasma. It is found that when a tissue thickness of 500 µm is used the H₂O₂ concentrations in organic liquids are about 20–30 times higher than in DDW. The and concentrations in serum liquid are much higher than in all other liquids, which might be due to the plasma reacting with amino acids and proteins. Besides, the concentration in organic solution is higher than the concentration for the same experimental conditions. Furthermore, when the serum percentage is increased from 2% to 10%, the concentration increases dramatically but the concentration decreases significantly. This is especially true for a tissue thickness of 500 µm. One novel discovery is the RONS do not only penetrate the tissue by diffusion—there are also reactions between the plasma and the liquid which affect the final RONS concentration.

In this study, a swirler combining the vane swirler and the plasma swirler is designed to control the flame lift-off height. The plasma swirler is located near the rim of the injector and the vane swirler is placed upstream of the plasma swirler. The vane swirler is employed to form a divergent flow to sustain the detached flame and the plasma swirler is adopted to control the flame lift-off height. The ionic wind clinging to the inner wall of the injector tube does not penetrate into the center, leaving the main stream flow in the central region largely undisturbed. Characteristics of the flow field are analyzed from the results of laser Doppler anemometry (LDA) measurement and mechanism of the flame lift-off control by the combined vane-plasma swirler is revealed. The flame lift-off locations calculated from the LDA measurement are consistent with those from direct observation. The dielectric barrier discharge (DBD) voltage influences the height of the flame lift-off with a linear relationship observed, which means the flame lift-off height can be controlled precisely by the DBD voltage without any mechanical movement or changing the mass flow rate. The combined vane-plasma swirler has the potential to improve the fuel flexibility, increase flame stability and attenuate the injector overheating.

Highlights

1. A combined vane-plasma swirler is designed to control the flame lift-off height.

2. Flame lift-off height can be adjusted by changing the voltage of the dielectric barrier discharge.

3. A linear relationship between flame lift-off height and the dielectric barrier discharge voltage is observed.

4. Flame lift-off control by the combined vane-plasma swirler is mainly associated with the aerodynamic effect.

5. The swirler can improve fuel flexibility, increase flame stability and attenuate injector overheating.

On the basis of first principles methods, we systematically investigate the electronic structures and magnetic properties of zigzag C₃N nanoribbons (ZCNNRs) with ribbon widths (N) from 4 to 12. The unsaturated ZCNNRs are predicted to be magnetic metals or magnetic nearly half-metals depending on the ribbon width. The magnetic moments of ZCNNRs mainly result from the edged C atoms. The magnetic interactions of the narrower ribbon widths between the opposite edges are sensitive to the tensile strains, and the magnetic stability of the wider nanorribons can be effectively improved by applying the tensile strains. The mechanism of magnetism in ZCNNRs can be well understood through the Stoner criterion. In addition, the effect of H passivation is also explored. The edge magnetism disappears after H passivation. For even N, the H-passivated ZCNNRs are semiconductors and the band gap decreases with the enlargement of ribbon width. Moreover, the H-passivated ZCNNRs undergo an indirect-to-direct band gap transition at N  =  12. For odd N, the ribbons exhibit metallicity due to the half-filled bands across the Fermi level at π/2a.

Based on first-principles calculations, the evolution of hybrid interface states (HISs) from a single spinterface to a magnetic molecular junction and their contribution to the spin-dependent electron transport are investigated. It is demonstrated that the spin polarization of HISs may be conserved or eliminated by relying on the spin configuration of the electrodes. By comparing the results of 1,4-benzene-dithiolate (1,4-BDT) and 1,3-benzene-dithiolate (1,3-BDT) magnetic junctions, the transport calculations explore two entirely different transmission abilities of HISs. An efficient transmission close to 1 is achieved for the 1,4-BDT junction while a strongly suppressed one (~0.1) is achieved for the 1,3-BDT junction. An apparent enhancement of magnetoresistance by HISs is realized in the 1,4-BDT junction. The intrinsic mechanism is revealed by analyzing the transmission pathway and interfacial structures. This work indicates the promising prospect of HISs in improving the performance of molecular spintronic devices in the case of suitable interfacial designs.

2D nanoporous silicon films (np-SiFs) are of great interest as a kind of platform system for thermoelectric materials. In this study, the thermal conductivity (TC) of periodic np-SiFs was investigated systematically in relation to their geometric parameters, including pore radius, pore period length, and film thickness in terms of the atomic-bond-relaxation correlation mechanism and continuous medium mechanics by using the phonon kinetic method with the Born–von Karman dispersion relation. It was found that the 2D np-SiFs with columnar nanopores have high surface-to-volume ratios and elastic interactions among nanopores, which will change the Debye temperature, modify the phonon dispersion relation, reduce phonon group velocity, and further lead to the reduction of TC. Our findings provide a fundamental insight into nanoscale thermal transport in nanoporous structures, and are also useful for the advance rational design of novel thermoelectric devices.

2D GeTe has been predicted to be a promising ferroelectric and channel material due to its excellent electronic, optical, and excitonic properties. Here, using density functional theory in combination with the non-equilibrium Green's function method, we demonstrate the potential application of GeTe in NO sensor. It is found that the top sites of Ge atoms are the preferential adsorption sites for all considered gas molecules. The calculated adsorption energy of NO molecule is the largest, which is explained by both the quantitative Bader charge results and the charge density difference and electron localization function. The high selectivity and sensitivity of the 2D GeTe to NO molecule are demonstrated through comparing the band structures and density of states of GeTe before and after molecules adsorption. The distinct I–V responses show a significant current increase after the adsorption of NO, confirming the high sensitivity and selectivity for NO detection. A faster recovery speed of GeTe comparing to other sensors is also demonstrated. Our results highlight the potential application of GeTe as an efficient gas sensor for identifying NO molecules.

A quantum mechanics (QM) calculation and molecular dynamics (MD) simulation are performed to investigate the interaction of 5-fluorouracil (5-Fu) anticancer drug with covalent organic frameworks (COFs). QM results indicate that the drug adsorption process on COF surface is exothermic, and the optimized complexes are stable. Furthermore, it is found that the hydrogen bond and π–π interactions are the most important factors in the stabilization of the COF/5-Fu complexes. The calculated electron densities and Laplacian at the intermolecular bond critical points using atoms-in-molecule method indicate the intermolecular interactions between COF and drug molecules have 'electrostatic' character. The natural bond orbital analysis indicates that the charge has been transferred from COF to 5-Fu in all complexes. MD results confirm that diffusion of 5-Fu molecule into the COF pores is slow and is in the range of the other porous materials, which is a crucial factor for the controlled drug release.

Surface photovoltage transients on solar junctions have often been associated with carrier lifetime in the literature. However, the carrier decay in a junction is not governed by a first order carrier decay, but resulting from a differential capacitance interacting with a differential conductivity. This phenomenon is well known as the Kane–Swanson formalism in an engineering context where the carrier density transient is measured by photoconductance with a microwave or infrared beam. In this work, we solve the same differential equations numerically to model the carrier decay in the large signal domain extending over five orders of carrier density. Since the surface voltage is linked to the carrier density by a logarithmic relation, we express the carrier decay as surface photovoltage transients. We show how from photovoltage transients, the same information as from photoconductance can be drawn. To demonstrate the method as a generic tool, it is applied to four types of solar cells, two monocrystalline silicon cells, a Perovskite solar cell, a transition metal oxide/silicon hybrid junction, and a CIGS solar cell. Acquiring photovoltage transients by Kelvin force microscopy allows working on partial junctions without top contact, speeding up research of future photovoltaic materials. Furthermore, parameters may be mapped with a better lateral resolution compared to microwave photoconductance.