Optical Properties of Metacrystals Based on Protein Nanocages

The optical properties of 3D metacrystals made of gold nanoparticles in protein nanocages are studied. These metacrystals have sizes of tens of micrometers and are of high structural and optical quality. Through microspectroscopy measurements and model calculations it is demonstrated that the metacrystals show plasmonic absorption in the green wavelength range and are largely transparent in the red and infrared ranges. By using empty nanocages as placeholders in the metacrystal lattice, it is possible to control how strongly the metamaterial absorbs. Measurements on a pyramidal metacrystal show that it deflects visible light. The deflection shows evidence for anomalous refraction at short wavelengths and normal refraction at long wavelengths. The refractive dispersion is ascribed to the optical dispersion relation of the plasmonic metamaterial.     

Novel Biocompatible Magnetoelectric MnFe2O4 Core@BCZT Shell Nano–Hetero-Structures with Efficient Catalytic Performance

Magnetoelectric (ME) small-scale robotic devices attract great interest from the scientific community due to their unique properties for biomedical applications. Here, novel ME nano hetero-structures based on the biocompatible magnetostrictive MnFe₂O₄ (MFO) and ferroelectric Ba_0.85Ca_0.15Zr_0.1Ti_0.9O₃ (BCZT) are developed solely via the hydrothermal method for the first time. An increase in the temperature and duration of the hydrothermal synthesis results in increasing the size, improving the purity, and inducing morphology changes of MFO nanoparticles (NPs). A successful formation of a thin epitaxial BCZT-shell with a 2–5 nm thickness is confirmed on the MFO NPs (77 ± 14 nm) preliminarily treated with oleic acid (OA) or polyvinylpyrrolidone (PVP), whereas no shell is revealed on the surface of pristine MFO NPs. High magnetization is revealed for the developed ME NPs based on PVP- and OA-functionalized MFO NPs (18.68 ± 0.13 and 20.74 ± 0.22 emu g⁻¹, respectively). Moreover, ME NPs demonstrate 95% degradation of a model pollutant Rhodamine B within 2.5 h under an external AC magnetic field (150 mT, 100 Hz). Thus, the developed biocompatible core–shell ME NPs of MFO and BCZT can be considered as a promising tool for non-invasive biomedical applications, environmental remediation, and hydrogen generation for renewable energy sources.     

Super‐Resolution Nonlinear Photothermal Microscopy

Super‐resolution fluorescence microscopy enables imaging of fluorescent structures beyond the diffraction limit. However, this technique cannot be applied to weakly fluorescent cellular components or labels. As an alternative, photothermal microscopy based on nonradiative transformation of absorbed energy into heat has demonstrated imaging of nonfluorescent structures including single molecules and ~1‐nm gold nanoparticles. However, previously photothermal imaging has been performed with a diffraction‐limited resolution only. Herein, super‐resolution, far‐field photothermal microscopy based on nonlinear signal dependence on the laser energy is introduced. Among various nonlinear phenomena, including absorption saturation, multiphoton absorption, and signal temperature dependence, signal amplification by laser‐induced nanobubbles around overheated nano‐objects is explored. A Gaussian laser beam profile is used to demonstrate the image spatial sharpening for calibrated 260‐nm metal strips, resolving of a plasmonic nanoassembly, visualization of 10‐nm gold nanoparticles in graphene, and hemoglobin nanoclusters in live erythrocytes with resolution down to 50 nm. These nonlinear phenomena can be used for 3D imaging with improved lateral and axial resolution in most photothermal methods, including photoacoustic microscopy.     

Viability of intertwined supply networks: extending the supply chain resilience angles towards survivability. A position paper motivated by COVID-19 outbreak

An intertwined supply network (ISN) is an entirety of interconnected supply chains (SC) which, in their integrity secure the provision of society and markets with goods and services. The ISNs are open systems with structural dynamics since the firms may exhibit multiple behaviours by changing the buyer-supplier roles in interconnected or even competing SCs. From the positions of resilience, the ISNs as a whole provide services to society (e.g. food service, mobility service or communication service) which are required to ensure a long-term survival. The analysis of survivability at the level of ISN requires a consideration at a large scale as resilience of individual SCs. The recent example of coronavirus COVID-19 outbreak clearly shows the necessity of this new perspective. Our study introduces a new angle in SC resilience research when a resistance to extraordinary disruptions needs to be considered at the scale of viability. We elaborate on the integrity of the ISN and viability. The contribution of our position study lies in a conceptualisation of a novel decision-making environment of ISN viability. We illustrate the viability formation through a dynamic game-theoretic modelling of a biological system that resembles the ISN. We discuss some future research areas.     

Photonic Microhand with Autonomous Action

Grabbing and holding objects at the microscale is a complex function, even for microscopic living animals. Inspired by the hominid‐type hand, a microscopic equivalent able to catch microelements is engineered. This microhand is light sensitive and can be either remotely controlled by optical illumination or can act autonomously and grab small particles on the basis of their optical properties. Since the energy is delivered optically, without the need for wires or batteries, the artificial hand can be shrunk down to the micrometer scale. Soft material is used, in particular, a custom‐made liquid‐crystal network that is patterned by a photolithographic technique. The elastic reshaping properties of this material allow finger movement, using environmental light as the only energy source. The hand can be either controlled externally (via the light field), or else the conditions in which it autonomously grabs a particle in its vicinity can be created. This microrobot has the unique feature that it can distinguish between particles of different colors and gray levels. The realization of this autonomous hand constitutes a crucial element in the development of microscopic creatures that can perform tasks without human intervention and self‐organized automation at the micrometer scale.     

Active Metamaterials with Negative Static Electric Susceptibility

Although well-established textbook arguments suggest that static electric susceptibility χ⁽⁰⁾ must be positive in “all bodies,” it has been pointed out that materials that are not in thermodynamic equilibrium are not necessarily subject to this restriction. Media with inverted populations of atomic and molecular energy levels have been predicted theoretically to exhibit a χ⁽⁰⁾ < 0 state, however the systems envisioned require reduced temperature, reduced pressure, and an external pump laser to maintain the population inversion. Further, the existence of χ⁽⁰⁾ < 0 has never been confirmed experimentally. Here, a completely different approach is taken to the question of χ⁽⁰⁾ < 0 and a design concept to achieve “true” χ⁽⁰⁾ < 0 is proposed based on active metamaterials with internal power sources. Two active metamaterial structures are fabricated that, despite still having their power sources implemented externally for reasons of practical convenience, provide evidence in support of the general concept. Effective values are readily achieved at room temperature and pressure and are tunable throughout the range of stability −1 < χ⁽⁰⁾ < 0, resulting in experimentally-determined magnitudes that are over one thousand times greater than those predicted previously. Since χ⁽⁰⁾ < 0 is the missing electric analog of diamagnetism, this work opens the door to new technological capabilities such as stable electrostatic levitation.     

Particulate inorganic carbon production within E. huxleyi blooms in subpolar and polar seas: a satellite time series study (1998–2013)

Making use of the OC CCI (Ocean Colour Climate Change Initiative) satellite data, and based on the developed both Emiliania huxleyi bloom contouring methodologies and binary masks, areas of coccolithophore growth were distinguished without supervision from locations of mass developments of other algae. On these grounds, and employing special processing algorithms, multi-year time series of variations in occurrence, surficial extent, and content of particulate inorganic carbon (PIC) within E. huxleyi blooming areas in the North, Norwegian, Greenland, Barents, and Bering Seas were obtained for the time period 1998–2013. Analysis of algorithmic processing of the OC CCI data permitted to reveal the spatio-temporal sequence of E. huxleyi blooming events in the above seas of the North Atlantic and Arctic Oceans. During the intra-annual cycle, E. huxleyi blooms advance from temperate to higher latitudes along the pathways of the Gulf Stream propagation to the north. Annually, the blooms arise in the vicinity of the Great Britain southern extremity, and further on move northward along the western coast of this Island Country, round it to eventually appear first in the North and Norwegian Seas (in early June), then in the Greenland Sea (in late June), and finally in the Barents Sea (in late July–early September). The regularities in dates of bloom outbreak and their duration are revealed. The bloom areas in the North Atlantic–Arctic water are the lowest in the Greenland Sea (10,000–30,000 km²) and by an order of magnitude higher in the Barents Sea. The same pattern holds for the total PIC content within E. huxleyi blooms: 400 t–14 kt in the Greenland Sea and about 0.35 Mt in the Barents Sea. In the Bering Sea, the temporal and spatial dynamics of E. huxleyi development proved to be highly irregular: before and after the 1997–2001 period of high intensity of this phenomenon, the blooms are sporadic, their extent and PIC production are either very low or insignificant. Regarding the range of E. huxleyi bloom areas in the Bering Sea during 1997–2001, it is rather similar to that of the Barents Sea. However, the PIC content in the Bering Sea, as compared to that in the Barents Sea, is higher by a factor of about two with maximum values reaching 0.4 Mt and, on one occasion (in 2001), even about 0.7 Mt.     

Controllable Generation of a Submillimeter Single Bubble in Molten Metal Using a Low-Pressure Macrosized Cavity

Metallurgical and Materials Transactions B - We develop a method for generation of a single gas bubble in a pool of molten metal. The method can be useful for applications and research studies...     

Active Control of Thermal Convection in a Rectangular Loop by Changing its Spatial Orientation

The problem of the automatic control of the fluid flow in a rectangular convective loop heated from below is studied theoretically and experimentally. The control is performed by using a feedback subsystem which changes the convection regimes by introducing small discrete changes in the spatial orientation of the loop with respect to gravity. We focus on effects that arise when the feedback controller operates with an unavoidable time delay, which is cause by the thermal inertia of the medium. The mathematical model of the phenomenon is developed. The dynamic regimes of the convection in the thermosyphon loop under control are studied. It is shown that the proposed control method can successfully stabilize not only a no-motion state of the fluid, but also time-dependent modes of convection including the irregular fluid flow at high values of the Rayleigh number. It is shown that the excessive gain of the proportional feedback can result in oscillations in the loop orientation exciting the unsteady convection modes. The comparison of the experimental data obtained for dielectric oil and dodecane with theory is given, and their good agreement is demonstrated.