Presence Of Flux Research Articles

Boosting energy levels in graphene magnetic quantum dots through magnetic flux and inhomogeneous gap

We study the effects of a magnetic flux and an inhomogeneous gap on the energy spectrum of graphene magnetic quantum dots (GMQDs). By considering the Dirac equation in the infinite mass framework, we can analytically obtain eigenspinor expressions. By applying boundary conditions, we obtain an energy spectrum equation in terms of system parameters such as radius, magnetic field, energy, flux, and gap. In the infinite limit, we recover Landau levels for graphene in a magnetic field. We show that the energy spectrum increases significantly in the presence of flux and a gap inside the GMQDs, which prolongs the lifetime of the trapped electron states. We show that higher flux also produces new Landau levels of negative angular momentum. Meanwhile, we find that the gap increases the separation between the electron and hole energy bands. As shown in the radial probability analysis, flux and gap emerge as influential factors in controlling electron mobility, affecting confinement, and prolonging the presence of quasi-bound states.

M-theory moduli from exceptional complex structures

We continue the analysis of the geometry of generic Minkowski mathcal{N} = 1, D = 4 flux compactifications in M-theory using exceptional generalised geometry, including the calculation of the infinitesimal moduli spaces. The backgrounds can be classified into two classes: type-0 and type-3. For type-0, we review how the moduli arise from standard de Rham cohomology classes. We also argue that, under reasonable assumptions, there are no appropriate sources to support compact flux backgrounds for this class and so the only solutions are in fact G2 geometries. For type-3 backgrounds, given a suitable {partial}^{prime }{overline{partial}}^{prime } -lemma, we show that the moduli can be calculated from a cohomology based on an involutive sub-bundle of the complexified tangent space. Using a simple spectral sequence we prove quite generally that the presence of flux can only reduce the number of moduli compared with the fluxless case. We then use the formalism to calculate the moduli of heterotic M-theory and show they match those of the dual Hull-Strominger system as expected.

Neumann-Rosochatius system for strings on I-brane

We study rigidly rotating and pulsating strings in the background of a 1+1 dimensional intersection of two orthogonal stacks of fivebranes in type IIB string theory by using the Neumann-Rosochatius (NR) model. Starting with the Polyakov action of the probe fundamental string we show that a generalised ansatz reduce the system into the one dimensional NR model in the presence of flux. The integrable construction of the model is exploited to analyze the rotating and oscillating string solution. We render the large J BMN-type expansion for the energy of rotating string states while the same for the oscillating string has been derived in long string and small angular momenta limit.

Development of advanced cold crucible melting of titanium alloys

Cold crucible is used to melt reactive metal scrap at elevated temperatures for high quality castings or to produce spherical powders for additive manufacturing. The most advanced crucibles have a small exit nozzle to pour the molten alloy through the bottom opening protected by graphite or ceramic material. The nozzle operates at high temperature and typically lasts several minutes, possibly adding contamination to the outflowing liquid metal. This paper presents new efforts to improve the technique with the aim to achieve a stable commercial process by introducing melting of scrap metal in the presence of liquid flux of different compositions to purify the liquid metal and to enhance thermal effectiveness. The crucial modification in avoiding contamination is a new type of the non-consumable nozzle made of copper segments and the second coil to supply a high frequency electromagnetic field in the vicinity of the nozzle. The nozzle entrance is protected by a thin solidified layer of the same alloy as the main melt. The AC electromagnetic field adds heating at the outflow, modifies the velocity field, gives a possibility to extract particles, and precludes entrainment of slag into the final casting or into the produced powder. The electromagnetic force permits to control the outflow rate and to increase the superheat of the metal at the outlet. The presence of flux permits shielding of the liquid metal from direct contact with the water-cooled side segments of the crucible. The paper demonstrates the effectiveness of numerical modelling to predict and investigate a variety of options in advancement of the cold crucible technique. Figs 8, Refs 13.

N-spike string in AdS3\xd7 S1 with mixed flux

Sigma model in AdS3× S3 background supported by both NS-NS and R-R fluxes is one of the most distinguished integrable models. We study a class of classical string solutions for N-spike strings moving in AdS3× S1 with angular momentum J in S1 ⊂ S5 in the presence of mixed flux. We observe that the addition of angular momentum J or winding number m results in the spikes getting rounded off and not end in cusp. The presence of flux shows no alteration to the rounding-off nature of the spikes. We also consider the large N-limit of N-spike string in AdS3× S1 in the presence of flux and show that the so-called Energy-Spin dispersion relation is analogous to the solution we get for the periodic-spike in AdS3− pp-wave ×S1 background with flux.

Brane current algebras and generalised geometry from QP manifolds. Or, \u201cwhen they go high, we go low\u201d

We construct a Poisson algebra of brane currents from a QP-manifold, and show their Poisson brackets take a universal geometric form. This generalises a result of Alekseev and Strobl on string currents and generalised geometry to include branes with worldvolume gauge fields, such as the D3 and M5. Our result yields a universal expression for the ’t Hooft anomaly that afflicts isometries in the presence of fluxes. We determine the current algebra in terms of (exceptional) generalised geometry, and show that the tensor hierarchy gives rise to a brane current hierarchy. Exceptional complex structures produce pairs of anomaly-free current subalgebras on the M5-brane worldvolume.

(Invited) Particulate Photocatalysts with Perovskite-Type Structures and Their Application in Water Splitting

Sunlight-driven water splitting is studied actively for production of renewable solar hydrogen as a storable and transportable energy carrier. Both the efficiency and scalability of water- splitting systems are essential factors for practical application of renewable solar hydrogen because of the low areal density of solar energy [1]. It is desirable to develop particulate photocatalysts and their reaction systems that efficiently split water, because such systems can be spread over wide areas by inexpensive processes potentially. The author’s group has studied various oxide and oxynitride semiconductors as photocatalysts for water splitting. In my talk, recent progress in photocatalytic materials and reactors will be presented with focus on perovskite-type materials.SrTiO3 loaded with proper cocatalysts has been known to be active in overall water splitting under ultraviolet light irradiation since 1980s. Recently, the apparent quantum yield (AQY) of this photocatalyst in overall water splitting has been improved drastically [2]. The author's group has found that doping Al3+ into the titanium site of SrTiO3 boosts the water splitting activity by two orders of magnitude [3]. By refining the preparation conditions of the Al-doped SrTiO3 (SrTiO3:Al) photocatalyst and the loading conditions of cocatalysts working as hydrogen and oxygen evolution sites, the AQY of overall water splitting has reached more than 90% at 365 nm [2], equivalent to an internal quantum efficiency of almost unity. This quantum efficiency is the highest yet reported and indicate that a particulate photocatalyst can drive the greatly endergonic overall water splitting reaction at a quantum efficiency comparable to values obtained from photon-to-chemical or photon-to-current conversion in photosynthesis or photovoltaic systems, respectively.Photocatalyst sheets based on SrTiO3:Al contained in a panel-type reactor split water into hydrogen and oxygen and release gas bubbles at a rate corresponding to a solar-to-hydrogen energy conversion efficiency of 10% under intense ultrviolet illumination even when the water depth is merely 1 mm [4]. Moreover, the photocatalyst can maintain 80% of its initial activity during 1300 h of constant simulated sunlight irradiation at ambient pressure with appropriate surface modifications [5]. A prototype 1-m2-sized panel reactor containing SrTiO3:Al photocatalyst sheets splits water under natural sunlight irradiation without a significant loss of the intrinsic activity of the photocatalyst sheets. A solar hydrogen production system with a greater size (100 m2) was recently built, and its performance and system characteristics are under investigation.SrTiO3:Al harvests only the ultraviolet light of the sunlight. It is essential to develop photocatalysts active under visible light irradiation. BaTaO2N is a visible light that can evolve hydrogen and oxygen from aqueous solutions containing sacrificial electron donors and acceptors, respectively. Recently, the AQYs of BaTaO2N in these sacrificial reactions have been improved significantly. Highly-crystalline BaTaO2N can be synthesized by directly nitriding a mixture of BaCO3 in the presence of RbCl flux [6]. The resultant BaTaO2N shows decent hydrogen evolution activity when a platinum cocatalyst is loaded by impregnation. By optimizing the cocatalyst loading conditions, the electron transfer from the BaTaO2N photocatalyst to the platinum cocatalyst, and thus the hydrogen evolution activity, was enhanced. The AQY of the resultant Pt-loaded BaTaO2N reached 6.8% at 420 nm in the sacrificial hydrogen evolution reaction. This is exceptionally high among nitride-type photocatalysts with visible light absorption of up to 650 nm.In conventional synthesis, BaTaO2N is nitrided from a mixture of BaCO3, Ta2O5, Ba- and Ta-containing complex oxides, often in the presence of flux. However, these starting materials have different crystal structures from the product BaTaO2N, and so the crystal structures have to be change during the nitridation. This is thought to induce defects in the product material. Therefore, a perovskite-type oxide with a Ba/Ta molar ratio of unity was designed, namely a complex oxide nominally denoted as Na1/4Ba3/4Zn1/4Ta3/4O3 [7]. This oxide can be nitrided into BaTaO2N because Na and Zn components are volatile at high temperature. The resultant BaTaO2N exhibited an AQY of 11.9% at 420 nm in the sacrificial oxygen evolution reaction after loading of a cobalt oxide cocatalyst. Hisatomi et al. Catal. 2019, 2, 387.Takata et al., Nature 2020, 581, 411.Ham et al., Mater. Chem. A 2016, 4, 3027.Goto et al., Joule 2018, 2, 509.Lyu et al. Sci. 2019, 10, 3196.Luo et al., Growth Des. 2020, 20, 255.Jadhav et al. J. Mater. Chem. A. 2020, 8, 1127.

Transcriptome integrated metabolic modeling of carbon assimilation underlying storage root development in cassava

The existing genome-scale metabolic model of carbon metabolism in cassava storage roots, rMeCBM, has proven particularly resourceful in exploring the metabolic basis for the phenotypic differences between high and low-yield cassava cultivars. However, experimental validation of predicted metabolic fluxes by carbon labeling is quite challenging. Here, we incorporated gene expression data of developing storage roots into the basic flux-balance model to minimize infeasible metabolic fluxes, denoted as rMeCBMx, thereby improving the plausibility of the simulation and predictive power. Three different conceptual algorithms, GIMME, E-Flux, and HPCOF were evaluated. The rMeCBMx-HPCOF model outperformed others in predicting carbon fluxes in the metabolism of storage roots and, in particular, was highly consistent with transcriptome of high-yield cultivars. The flux prediction was improved through the oxidative pentose phosphate pathway in cytosol, as has been reported in various studies on root metabolism, but hardly captured by simple FBA models. Moreover, the presence of fluxes through cytosolic glycolysis and alanine biosynthesis pathways were predicted with high consistency with gene expression levels. This study sheds light on the importance of prediction power in the modeling of complex plant metabolism. Integration of multi-omics data would further help mitigate the ill-posed problem of constraint-based modeling, allowing more realistic simulation.

<p><strong>Synopsis of <em>Euphorbia</em> section <em>Anisophyllum</em> (Euphorbiaceae) in Italy, with an insight on variation of distribution over time in Tuscany</strong></p>

We present an updated taxonomic study of Euphorbia sect. Anisophyllum (Euphorbiaceae) for Italy. A comprehensive body of knowledge has been developed thanks to the examination of about 1,250 herbarium specimens from 13 Italian herbaria, field surveys, and an extensive literature analysis. As a result, our revision included 10 species considered as currently occurring in Italy, of which 2 native (Euphorbia chamaesyce and E. peplis) and 8 alien (E. glyptosperma, E. humifusa, E. hypericifolia, E. maculata, E. nutans, E. ophthalmica, E. prostrata, and E. serpens). The revision included also additional 5 species previously erroneously recorded in Italy (E. berteroana, E. engelmannii, E. hyssopifolia, E. indica, and E. thymifolia) and other two species (E. hirta and E. humistrata) not occurring in Italy but closely related to recorded species and already established and considered as alien species in other countries. Current distribution and status at the regional level is updated for 7 species (E. berteroana, E. engelmannii, E. humifusa, E. hypericifolia, E. indica, E. nutans, and E. prostrata) and typification of 18 names (Chamaesyce glomerifera, E. boliviana, E. bracteolaris, E. brasiliensis, E. chamaesyce var. maculata, E. engelmannii, E. humifusa, E. hypericifolia var. communis, E. indica, E. klotzschiana, E. nutans, E. peplis, E. perforata, E. pinnulosa, E. preslii, E. procumbens, E. reichenbachiana, and E. trichogona) is also provided. For all taxa we report information about nomenclature, morphology, ecology, chorology, distribution, taxonomy, as well as an identification key for species identification and original photos. In addition, we provided a detailed statement of species of the section for Tuscany and we performed an analysis of distribution variation of different species over time in this region. Our results evaluate the current state of E. sect. Anisophyllum in Italy and highlight the presence of fluxes in densities of different species populations. In particular, a reduction of native and formerly colonizing species and an increase of more recently colonizing species is recorded.

6D (1,1) gauged supergravities from orientifold compactifications

We study dimensional reductions of M-theory/type II strings down to 6D in the presence of fluxes and spacetime filling branes and orientifold planes of different types. We classify all inequivalent orientifold projections giving rise to mathcal{N} = (1, 1) supergravities in 6D and work out the embedding tensor/fluxes dictionary for each of those. Finally we analyze the set of vacua for the different classes of reductions and find an abundance of “no-scale” type Minkowski vacua, as well as a few novel examples of (A)dS extrema.

The type IIA flux potential, 4-forms and Freed-Witten anomalies

We compute the full classical 4d scalar potential of type IIA Calabi-Yau orientifolds in the presence of fluxes and D6-branes. We show that it can be written as a bilinear form V = ZABρAρB, where the ρA are in one-to-one correspondence with the 4-form fluxes of the 4d effective theory. The ρA only depend on the internal fluxes, the axions and the topological data of the compactification, and are fully determined by the Freed-Witten anomalies of branes that appear as 4d string defects. The quadratic form ZAB only depends on the saxionic partners of these axions. In general, the ρA can be seen as the basic invariants under the discrete shift symmetries of the 4d effective theory, and therefore the building blocks of any flux-dependent quantity. All these polynomials may be obtained by derivation from one of them, associated to a universal 4-form. The standard mathcal{N}=1 supergravity flux superpotential is uniquely determined from this master polynomial, and vice versa.

Impact of thermal treatment of calcium silicate-rich slag on the removal of cadmium from aqueous solution

The problem of wastewater treatment and inorganics removal and the waste management including slags is of great importance nowadays. Three types of treated calcium silicate-rich slags were tested. The impact of thermal treatment of slag in air (SA), under NH3 atmosphere (SN), and in the presence of flux (SF) at different temperatures (500–1000 °C) on removal of cadmium from aqueous solution was investigated. The treatment had the impact on slag characteristics. In the slag samples thermally treated in air, SiO2, clinopyrexene, larnite, CaSiO3, Ca3SiO5, Ca8Si5O18, and olivine crystalline phases were formed. A very similar trend was observed for the slag samples heat treated under NH3 atmosphere except the formation of wollastonite at 1000 °C. Depending on the flux employed in the thermal treatment of slag, various crystalline phases were formed. Each alkaline earth metal chloride (CaCl2, SrCl2, and BaCl2) flux affected differently. Potassium, iron, magnesium, aluminum, silicon, calcium, and lead are the main elemental components of the slag. The slag sample thermally treated with CaCl2 flux showed the highest potential for Cd(II) adsorption followed by the SN sample series. The results strictly indicate the complex mechanism of Cd(II) adsorption onto the slag materials considering both chemical adsorption (a pseudo-second order) and intraparticle diffusion. Cd(II) adsorption proceeded according to the Langmuir, Temkin or Freundlich models. The best results can be obtained using a low-cost slag adsorbent thermally treated under NH3 atmosphere.

Effect of Graphene Layers on Phenomena Occurringat Interface of Sn-Zn-Cu Solder and Cu Substrate

Cu and graphene-coated Cu substrates spread with Sn-Zn eutectic-based alloy containing 0.5 wt.%, 1 wt.%, or 1.5 wt.% Cu have been studied at 250°C. Soldering experiments were performed for wetting time of 3 min, 8 min, 15 min, 30 min, and 60 min in (1) presence of flux without argon protective atmosphere and (2) fluxless in argon atmosphere. Solidified solder–pad couples were cross-sectioned and examined using scanning electron microscopy with energy-dispersive spectroscopy to study their interfacial microstructure. To assess the effect of graphene coating on solder, Cu pads were covered by graphene using chemical vapor deposition. The results revealed that the liquid solder did not wet the graphene-coated copper in the absence of flux. Wetting took place only with use of flux, because it destroyed the graphene layer and enabled contact of the liquid solder with the copper. Experiments were designed to demonstrate the effect of Cu addition and graphene coating on the kinetics of the formation and growth of Cu5Zn8 and CuZn4 phases identified by x-ray diffraction analysis, Raman spectroscopy, and energy-dispersive spectroscopy. A decrease of about 60% in the thickness of the intermetallic layer was observed when applying the graphene interlayer in presence of flux. Addition of copper to the Sn-Zn alloy improved the wettability as the copper content was increased.

T4 fibrations over Calabi–Yau two-folds and non-Kähler manifolds in string theory

We construct a geometric model of eight-dimensional manifolds and realize them in the context of type II string theory. These eight-manifolds are constructed by non-trivial T4 fibrations over Calabi–Yau two-folds. These give rise to eight-dimensional non-Kähler Hermitian manifolds with SU(4) structure. The eight-manifold is also a circle fibration over a seven-dimensional G2 manifold with skew torsion. The eight-manifolds of this type appear as internal manifolds with SU(4) structure in type IIB string theory with F3 and F7 fluxes. These manifolds have generalized calibrated cycles in the presence of fluxes.

Laser welding studies on Ti-6Al-4V in air in conjunction with cathodic protection

Laser beam melting of titanium alloy Ti-6Al-4V was performed with an Yb-fibre laser to produce weld pools under a range of conditions. These included the use of a flux covering of molten CaF2 or a molten mixture of CaF2 and NaF, in an atmosphere of ambient air, either with or without the application of cathodic protection to the Ti-6Al-4V. As anticipated, in the absence of flux, considerable oxidation of the metal occurred. In contrast, in the presence of flux, the degree of oxidation was greatly reduced. In addition, the application of a modest cathodic potential to the flux-covered metal reduced the pick-up of oxygen even further. The results suggest that the use of an appropriate flux combined with cathodic protection when fusion welding titanium and its alloys may offer advantages in circumstances where inert gas shielding is not always feasible, for example, in certain site welding applications.

Massive quiver matrix models for massive charged particles in AdS

We present a new class of ${\cal N}=4$ supersymmetric quiver matrix models and argue that it describes the stringy low-energy dynamics of internally wrapped D-branes in four-dimensional anti-de Sitter (AdS) flux compactifications. The Lagrangians of these models differ from previously studied quiver matrix models by the presence of mass terms, associated with the AdS gravitational potential, as well as additional terms dictated by supersymmetry. These give rise to dynamical phenomena typically associated with the presence of fluxes, such as fuzzy membranes, internal cyclotron motion and the appearance of confining strings. We also show how these models can be obtained by dimensional reduction of four-dimensional supersymmetric quiver gauge theories on a three-sphere.

Optimization of Cu–Ag Core–Shell Solderless Interconnect Paste Technology

The use of Cu–Ag core–shell nanoparticles has been proposed as a Pb-free interconnect technology in which upon annealing, the Ag shell dewets the copper surface and forms Ag necks between Cu core particles at particle–particle contacts. Neck formation creates an electrically, thermally, and mechanically stable porous sintered network. To convert this concept into a viable manufacturing technology, optimization of particle characteristics and paste formulation is necessary with respect to sinterability, mechanical strength, and processability for typical die attach and possibly surface mount assembly reflow operations and applications. This paper describes the optimization process carried out using three core–shell powder configurations and over 50 flux formulations. The two best performing pastes consisted of 1- $\mu \text{m}$ diameter core–shell particles with a 9-nm Ag shell and fluxes containing methyl ethyl ketone, isopropanol, methyl pyrrolidone, butyl cellosolve, Terpineol, Teckros D85, Troythix XYZ, and malonic acid. These pastes exhibited the targeted shear thinning behavior necessary for screen printing and assembly processing. From a comparison of the microstructural evolution for paste and dry compacts, the presence of flux did not appear to inhibit neck formation. As the final step, printability optimization using commercial assembly equipment was performed based on squeegee speed and pressure and showed coverage and paste rheology to be comparable with those of commercial Pb-free solder pastes.

Generalized complex geometry of pure backgrounds in 10 and 11 dimensions

Pure backgrounds are a natural generalization of supersymmetric Calabi–Yau compactifications in the presence of flux. They are described in the language of generalized structures and generalized complex geometry, and they exhibit some interesting general patterns: the internal manifold is generalized Calabi–Yau, whereas the Ramond–Ramond flux is exact in a precise sense, as discussed in this paper. We have shown that although these two characteristics do persist in the case of generic 10-dimensional Euclidean type II pure backgrounds, they do not capture the full content of supersymmetry. We also discuss the uplift of real Euclidean type IIA pure backgrounds to supersymmetric backgrounds of Lorentzian 11-dimensional supergravity.

Part II. Model for the Protective Coating Formation During Hot Dip Galvanizing/ Część II. Model Formowania Powłoki Ochronnej Podczas Cynkowania Ogniowego

Abstract A mathematical description for the (Zn) - coating formation with the presence of flux in the zinc bath is presented. This description includes the progressive vanishing of the products of the flux disintegration. A function which expresses the flux vanishing is formulated. The solidification of some phase sub-layers in the (Zn) - coating is considered with the use of a hypothetical pseudo-ternary phase diagram Fe-Zn-flux. Some relationships are formulated to define the varying Zn - solute redistribution as observed across the sub-layers. The relationships are based on the mass balance analyzed for the coating / bath / flux system. An amount of the growing phase in a given sub-layers is also defined mathematically.

F-term axion monodromy inflation

The continuous shift symmetry of axions is at the heart of several realizations of inflationary models. In particular, axion monodromy inflation aims at achieving super-Planckian field ranges for the inflaton in the context of string theory. Despite the elegant underlying principle, explicit models constructed hitherto are exceedingly complicated. We propose a new and better axion monodromy inflationary scenario, where the inflaton potential arises from an F-term. We present several scenarios, where the axion arises from the Kaluza-Klein compactification of higher dimensional gauge fields (or p-form potentials) in the presence of fluxes and/or torsion homology. The monodromy corresponds to a change in the background fluxes, and its F-term nature manifests in the existence of domain walls interpolating among flux configurations. Our scenario leads to diverse inflaton potentials, including linear large field behaviour, chaotic inflation, as well as potentials with even higher powers. They provide an elegant set of constructions with properties in the ballpark of the recent BICEP2 observational data on primordial gravitational waves.