Abstract: To provide for the globally increasing demand for proteinaceous food, microbial protein (MP) has the potential to become an alternative food or feed source. Phosphorus (P), on the other hand, is a critical raw material whose global reserves are declining. Growing MP on recovered phosphorus, for instance, struvite obtained from wastewater treatment, is a promising MP production route that could supply protein-rich products while handling P scarcity. The aim of this study was to explore struvite dissolution kinetics in different MP media and characterize MP production with struvite as sole P-source. Different operational parameters, including pH, temperature, contact surface area, and ion concentrations were tested, and struvite dissolution rates were observed between 0.32 and 4.7 g P/L/d and a solubility between 0.23 and 2.22 g P-based struvite/L. Growth rates and protein production of the microalgae Chlorella vulgaris and Limnospira sp. (previously known as Arthrospira sp.), and the purple non‑sulfur bacterium Rhodopseudomonas palustris on struvite were equal to or higher than growth on conventional potassium phosphate. For aerobic heterotrophic bacteria, two slow-growing communities showed decreased growth on struvite, while the growth was increased for a third fast-growing one. Furthermore, MP protein content on struvite was always comparable to the one obtained when grown on standard media. Together with the low content in metals and micropollutants, these results demonstrate that struvite can be directly applied as an effective nutrient source to produce fast-growing MP, without any previous dissolution step. Combining a high purity recovered product with an efficient way of producing protein results in a strong environmental win-win.

Abstract: In iets meer dan 30 jaar moeten we tot 50% meer eiwit produceren, terwijl onze conventionele lineaire voedselproductieketen reeds de grenzen van duurzaamheid overschrijdt. Microbieel eiwit (MP), de eiwitrijke biomassa van micro-organismen, werd onderzocht als nieuw voeder en voedselingrediënt in een circulaire eiwitproductieketen. MP-productie kan gebaseerd zijn op primaire grondstoffen om zo de inefficiënte stappen in de huidige eiwitproductie over te slaan, of de productie kan gebaseerd zijn op secundaire grondstoffen afkomstig van de verliezen in de conventionele productieketen (bijvoorbeeld afvalwater). Zowel indirecte als directe strategiën voor nutriëntenherwinning kunnen geïdentificeerd worden. Indirecte nutriëntenherwinning werd onderzocht door struviet toe te passen als fosfor- en stikstofbron voor MP-productie. Struviet, een herwinningsproduct in de afvalwaterzuivering, bleek een hoge zuiverheidsgraad te hebben waardoor het een uitstekende selectieve barrière vormt tussen afvalstroom en MP productie. Oplossingssnelheden en MP groei-experimenten toonden aan dat struviet gemakkelijk gedoseerd kan worden in functie van de microbiële nutriëntenbehoeftes, waarnaast problemen vermeden worden gerelateerd aan de turbiditeit van nevenstromen, wat de productie van fototrofe MP mogelijk maakt. Daarnaast werd ook directe nutriëntenherwinning onderzocht. Hierbij werden de voedingswaarde en veiligheid geanalyseerd van biomassa bestaande uit aerobe heterotrofe bacteriën (AHB) afkomstig van effluentzuivering van 25 bedrijven in de voedings- en drankensector. Verder werd ook de temporele variabiliteit in kaart gebracht. Er werd een veelbelovend eiwitgehalte geobserveerd waarvan de variabiliteit aanzienlijke was. Verder werd aangetoond dat het eiwitgehalte positief gecorreleerd was met stikstofbelasting en negatief met slibverblijftijd, wat een indicatie is dat de implementatie van een geoptimaliseerd productieproces, de biomassakwaliteit gevoelig kan verhogen. Bovendien was de veiligheid als veevoeder gegarandeerd op vlak van de meeste contaminanten. In het daarop volgende hoofdstuk werd de variabiliteit in voedingswaarde en veiligheid bestudeerd van commerciële fototrofe MP (de microalgen Chlorella en Spirulina), gekweekt op primaire grondstoffen. De waargenomen variabiliteit in voedingswaarde vereist verdere optimalisatie van het productieproces. Er werd ook waargenomen dat een hoog eiwitgehalte geen hoge totale voedingswaarde impliceert, omdat de verteerbaarheid en de eiwitkwaliteit nog steeds ongunstig kunnen zijn. Op basis van gemeten contaminanten geeft een veilige consumptiedosis aan dat microalgen perfect kunnen worden geconsumeerd als volwaardige eiwitbron in plaats van als supplement, hun huidige hoofdtoepassing. In een laatste experimenteel hoofdstuk werd onderzocht hoe de variabiliteit in biomassakwaliteit van microalgen kan worden gereduceerd en hoe een stabiele, hoogwaardige biomassaproductie kan worden bekomen. De invloed van oogsttijd, operationele modus en fotoperiode werd bepaald op de productiviteit van biomassa, eiwit en essentiële aminozuren en er werden optimale productieparameters geïdentificeerd. Samengevat is MP-productie op basis van indirecte en directe nutriëntenherwinning veelbelovend. Verdere technologische ontwikkelingen en het verhogen van bewustwording en sociale acceptatie, moeten een verdere introductie van MP in de voeder- en voedingsmarkt faciliteren. Hier kan MP een belangrijke oplossing vertegenwoordigen om de exponentieel groeiende wereldbevolking op een duurzame manier te voeden.

Abstract: An electron-irradiation-induced transformation from cubic beta2 austenite to monoclinic 7M martensite was observed in situ under high resolution electron microscopy conditions in a thin foil of Ni63Al37 beta2 phase (B2, CsCl structure), with the start temperature of the martensitic transformation below but very close to room temperature. The structure of the martensite is consistent with thermoelastic or stress-induced martensite at this composition, including the existence of multiple stacking faults. The transformation is described by a gradual increase in the shear and shuffle amplitudes already existing in the precursor domains. Possible origins of the transformation are discussed.

Abstract: Heterostructures composed of two-dimensional (2D) materials are already opening many new possibilities in such fields of technology as electronics and magnonics, but far more could be achieved if the number and diversity of 2D materials is increased. So far, only a few dozen 2D crystals have been extracted from materials that exhibit a layered phase in ambient conditions, omitting entirely the large number of layered materials that may exist in other temperatures and pressures. Here, we demonstrate how these structures can be stabilized in 2D van der Waals stacks under room temperature via growing them directly in graphene encapsulation by using graphene oxide as the template material. Specifically, we produce an ambient stable 2D structure of copper and iodine, a material that normally only occurs in layered form at elevated temperatures between 645 and 675 K. Our results establish a simple route to the production of more exotic phases of materials that would otherwise be difficult or impossible to stabilize for experiments in ambient.

Abstract: We report the complete disappearance of the structural modulation in heavily lead-doped Bi2-xPbxSr2CaCu2O8+delta crystals observed by transmission electron microscopy. Crystals with a nominal lead content of x = 0.8, corresponding to an effective lead content of x = 0.39, yield the non-modulated phase. The superconducting properties of this modulation-free phase (beta phase) have been studied and compared to those of undoped crystals displaying the modulated phase (alpha phase). Magnetisation measurements reveal that the irreversibility field H-irr(T) and relaxation rates are strongly improved within the beta phase. Measurements of the lower critical field, H-c1, show that the anisotropy factor, epsilon, is considerably reduced in the modulation-free crystals. This is the signature of stronger coupling between CuO2 layers which in turn deeply influences the effectiveness of the pinning. These measurements explain the enhanced pinning properties in moderately Pb-doped crystals in which the alpha phase and beta phase coexist. The enhanced pinning is not only due to the alpha/beta interfaces, which act as effective pinning centers: the emergence of modulation-free domains, characterized by a strongly reduced anisotropy, also significantly contribute to this effect. (C) 2003 Elsevier B.V. All rights reserved.

Abstract: In this work, photoelectric yield and electrical properties of several types of epitaxial erbium silicide on silicon Schottky diodes are studied, Different preparation conditions are used simultaneously on n- and p-Si(111) substrates for the 200 Angstrom thick silicide films. A last type of sample consists in 1.3 monolayer of epitaxial silicide with root 3 X root 3 superstructure on the Si substrate and covered by silver on the top. Photocurrent measurements are done as a function of photon energy at several temperatures. All these samples show barrier heights near 1 eV on p-type Si, even for the interface comprising only 1.3 monolayer of silicide whereas barrier heights on n-rype Si span the range from 0.28 to 0.67 eV for this last kind of sample, the sum of the barriers always exceeding the silicon band gap, These photoelectric results are confirmed by electrical characterisations, All these results show that the Fermi level is pinned 0.1 eV below the conduction band edge on p-type Si but shifts to various positions lower within the band gap on n-type Si. This fact leads to the hypothesis of a density of -7 interface states close to the charge change in the Si depletion zone from p- to n-type, namely 10(12) eV(-1) cm(-2). Although some inhomogeneities and defects at the interface are detected by electron microscopy for samples annealed at 750 degrees C, Fermi level position seems rather insensitive to the structural details of the interface while the silicide thickness plays a role on n-type Si.

Abstract: Using a numerical tight-binding approach based on the Chebyshev–Bogoliubov–de Gennes method we describe Josephson junctions made of multilayer graphene contacted by top superconducting gates. Both Bernal (ABA) and rhombohedral (ABC) stacking are considered and we find that the type of stacking has a strong effect on the proximity effect and the supercurrent flow. For both cases the pair amplitude shows a polarization between dimer and nondimer atoms, being more pronounced for rhombohedral stacking. Even though the proximity effect in nondimer sites is enhanced when compared to single-layer graphene, we find that the supercurrent is suppressed. The spatial distribution of the supercurrent shows that for Bernal stacking the current flows only in the topmost layers while for rhombohedral stacking the current flows throughout the whole structure.

Abstract: Using highly efficient GPU-based simulations of the tight-binding Bogoliubov-de Gennes equations we solve self-consistently for the pair correlation in rhombohedral (ABC) and Bernal (ABA) multilayer graphene by considering a finite intrinsic s-wave pairing potential. We find that the two different stacking configurations have opposite bulk/surface behavior for the order parameter. Surface superconductivity is robust for ABC stacked multilayer graphene even at very low pairing potentials for which the bulk order parameter vanishes, in agreement with a recent analytical approach. In contrast, for Bernal stacked multilayer graphene, we find that the order parameter is always suppressed at the surface and that there exists a critical value for the pairing potential below which no superconducting order is achieved. We considered different doping scenarios and find that homogeneous doping strongly suppresses surface superconductivity while nonhomogeneous field-induced doping has a much weaker effect on the superconducting order parameter. For multilayer structures with hybrid stacking (ABC and ABA) we find that when the thickness of each region is small (few layers), high-temperature surface superconductivity survives throughout the bulk due to the proximity effect between ABC/ABA interfaces where the order parameter is enhanced. DOI: 10.1103/PhysRevB.87.134509

Abstract: The ordered configurations of a monolayer of interacting magnetic dipoles confined in a circular parabolic potential are investigated as a function of the dipole moment of the particles. Despite the circular confinement, we find very asymmetric ordered structures like chains and Y-shaped configurations when a magnetic field is applied parallel to the plane of the particles. The normal-mode spectrum of the particles and its dependence on the magnetic field and the strength of the dipole moment of the particles are studied. The vibrational and rotational modes of the spectrum, which are associated with the stability of the system, are investigated in detail. The number of particles is varied and we found different ordering of the particles for different values of the dipole moment and the magnetic field. A ring structure with a large number of particles is observed for high values of the dipole moment of the particles.

Abstract: This study addresses the comparison of scanning transmission electron microscopy (STEM) measurements of momentum transfers using the first moment approach and the established method that uses segmented annular detectors. Using an ultrafast pixelated detector to acquire four-dimensional, momentum-resolved STEM signals, both the first moment calculation and the calculation of the differential phase contrast (DPC) signals are done for the same experimental data. In particular, we investigate the ability to correct the segment-based signal to yield a suitable approximation of the first moment for cases beyond the weak phase object approximation. It is found that the measurement of momentum transfers using segmented detectors can approach the first moment measurement as close as 0.13 h/nm in terms of a root mean square (rms) difference in 10 nm thick SrTiO3 for a detector with 16 segments. This amounts to 35% of the rms of the momentum transfers. In addition, we present a statistical analysis of the precision of first moment STEM as a function of dose. For typical experimental settings with recent hardware such as a Medipix3 Merlin camera attached to a probe-corrected STEM, we find that the precision of the measurement of momentum transfers stagnates above certain doses. This means that other instabilities such as specimen drift or scan noise have to be taken into account seriously for measurements that target, e.g., the detection of bonding effects in the charge density.

Abstract: We report the mapping of polarization-induced internal electric fields in AlN/GaN nanowire heterostructures at unit cell resolution as a key for the correlation of optical and structural phenomena in semiconductor optoelectronics. Momentum-resolved aberration-corrected scanning transmission electron microscopy is employed as a new imaging mode that simultaneously provides four-dimensional data in real and reciprocal space. We demonstrate how internal mesoscale and atomic electric fields can be separated in an experiment, which is verified by comprehensive dynamical simulations of multiple electron scattering. A mean difference of 5.3 +- 1.5 MV/cm is found for the polarization-induced electric fields in AlN and GaN, being in accordance with dedicated simulations and photoluminescence measurements in previous publications.