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A SPECTRAL-IN-TIME NEWTON-KRYLOV METHOD FOR NONLINEAR PDE-CONSTRAINED OPTIMIZATION
No full textWe devise a method for nonlinear time-dependent PDE-constrained optimization problems that uses a spectral-in-time representation of the residual, combined with a Newton-Krylov method to drive the residual to zero. We also propose a preconditioner to accelerate this scheme. Numerical results indicate that this method can achieve fast and accurate solution of nonlinear problems for a range of mesh sizes and problem parameters, the numbers of outer Newton and inner Krylov iterations required to reach the attainable accuracy of a spatial discretization are robust with respect to the number of collocation points in time, and also do not change substantially when other problem parameters are varied
Ethical responsibilities of tenured academics supervising non-tenured researchers in times of neoliberalism and precarity
No full textNeoliberal reform of the university sector has resulted in increasing numbers of academics employed on casual or fixed-term contracts. While there is an emergent body of literature on issues of precarity in the academy, relatively little attention has been paid to the roles and responsibilities of those tenured academics who employ and manage non-tenured researchers. The work involved in hiring and managing a contract researcher is rarely acknowledged or supported, and managers receive little to no training. In this paper, we draw on Dorothy Smith’s feminist sociological approach to analyse interviews with 22 non-tenured researchers to examine how managerial relationships shape the employment experiences of those working precariously. We argue that tenured academics have ethical responsibilities to provide a working environment that is fair, supports the ongoing development and wellbeing of non-tenured staff and challenges dominant discourses of precarious academics as ‘other’
Shell Filling and Trigonal Warping in Graphene Quantum Dots
No full textTransport measurements through a few-electron circular quantum dot in bilayer graphene display bunching of the conductance resonances in groups of four, eight and twelve. This is in accordance with the spin and valley degeneracies in bilayer graphene and an additional threefold 'minivalleydegeneracy' caused by trigonal warping. For small electron numbers, implying a small dot size and a small displacement field, a two-dimensional s- and then a p-shell are successively filled with four and eight electrons, respectively. For electron numbers larger than 12, as the dot size andthe displacement field increase, the single-particle ground state evolves into a three-fold degenerate minivalley ground state. A transition between these regimes is observed in our measurements and can be described by band-structure calculations. Measurements in magnetic field confirm Hund'ssecond rule for spin filling of the quantum dot levels, emphasizing the importance of exchange interaction effects
Atomium: The astounding complexity of the near circumstellar environment of the M-type AGB star R Hydrae:I. Morpho-kinematical interpretation of CO and SiO emission
No full textEvolved low to intermediate mass stars are known to shed their gaseous envelope into a large dusty molecule-rich circumstellar nebula which typically develop a high degree of structural complexity. Most of the large-scale, spatially correlated structures in the nebula are thought to originate from the interaction of the stellar wind with a companion. As part of the Atomium large programme, we observed the M-type asymptotic giant branch star R Hydrae with the Atacama Large Millimeter/submillimeter Array (ALMA). The morphology of the inner wind of R Hya —which has a known companion at ∼3500 au — was determined from maps of CO and SiO obtained at high angular resolution. A map of the CO emission reveals a multi-layered structure consisting of a large elliptical feature at an angular scale of ∼10”, that is oriented along the North–South axis. The wind morphology within the elliptical feature is dominated by two hollow bubbles. The bubbles are on opposite sides of the AGB star and lie along an axis with a position angle of ∼115º. Both bubbles are offset from the central star, and its appearance in the SiO channel maps indicates that the two bubbles might be shock waves travelling through the AGB wind. An estimate of the dynamical age of the bubbles yields an age of the order of a hundred years, which is in agreement with the previously proposed elapsed time since the star last underwent a thermal pulse. When the CO and SiO emission is examined on sub-arcsecond angular scales, there is evidence for an inclined, differentially rotating equatorial density enhancement, strongly suggesting the presence of a second nearby companion. The major axis of the position angle of this disk is ∼70º, in the plane of the sky. We tentatively estimate that a lower limit on the mass of the nearby companion is ∼0.65 M, on the basis of the highest measured speeds in the disk and the location of its inner rim at ∼6 au from the AGB star
E2 enzymes in genome stability: pulling the strings behind the scenes
No full textUbiquitin and ubiquitin-like proteins (UBLs) function as critical post-translational modifiers in the maintenance of genome stability. Ubiquitin/UBL-conjugating enzymes (E2s) are responsible, as part of a wider enzymatic cascade, for transferring single moieties or poly-chains of ubiquitin/UBLs to one or multiple residues on substrate proteins. Recent advances in structural and mechanistic understanding of how ubiquitin/UBL substrate attachment is orchestrated indicate that E2s can exert control over chain topology, substrate-site specificity and downstream physiological effects to help maintain genome stability. Drug discovery efforts have typically focussed on modulating other members of the ubiquitin/UBL cascades, or the ubiquitin-proteasome system. Here, we review the current standing of E2s in genome stability and revisit their potential as pharmacological targets for developing novel anti-cancer therapies
Energy efficient production of 5-hydroxymethylfurfural (5-HMF) over surface functionalized carbon superstructures under microwave irradiation
No full textMicrowave (MW)-assisted process intensification of catalytic conversion of saccharides is a promising route for energy efficient production of value-added chemicals and fuels. This work presents the development of the MW-responsive catalysts (i.e., the acid functionalized spherical carbon superstructure, SCS) for converting fructose to 5-HMF effectively and efficiently under MW irradiation. Under a mild MW condition (at 70 C, atmospheric pressure), the SCS catalyst (with surface sulfonic and carboxylic acid groups) achieved fructose conversion of ~97.8% and selectivity to 5-HMF of ~90.6% after 5 min reaction time with good recyclability, being significantly higher than that obtained by the system under the conventional heating. Importantly, the MW-assisted system showed very high energy efficiency coefficient of 1.01 mmol kJ−1 L−1 compared to that (0.09 mmol kJ−1 L−1) of the conventional thermal catalysis. The mechanism of process intensification of the system developed may be attributed to the combination of the dipole polarization of the MW-responsive sulfonic groups and the selective heating of the MW-absorbing SCS support under the MW condition
High performance thin film IGZO Schottky diodes with sputtered PdOx anode
No full textThin film Schottky barrier diodes (SBDs) based on amorphous oxide semiconductors play an important role in flexible and wearable electronics. In this work, thin film SBDs based on indium-gallium-zinc-oxide (InGaZnO or IGZO) were fabricated with sputtered PdOx/Pd top Schottky contact and low temperature (100 ℃ ) annealing in air atmosphere. The PdOx produces an oxygen-rich stoichiometry in the Schottky interface, resulting in high quality contact with rather low interface trap state density of 2.6×1017 cm-3 and extremely low barrier inhomogeneity of 0.01 eV. As a result, high performance IGZO SBDs were achieved with high on/off ratio of 3×107, near-unity ideality factor of 1.04, barrier height of 0.85 eV, high on-current density of 2.5 A·cm-2 at 1 V, and high reverse breakdown voltage of ~12 V
Microrheology of colloidal suspensions via Dynamic Monte Carlo simulations
No full textUnderstanding the rheology of colloidal suspensions is crucial in the formulation of a wide selection of industry-relevant products, such as paints, foods and inks. To characterise the viscoelastic behaviour of these soft materials, one can analyse the microscopic dynamics of colloidal tracers diffusing through the host fluid and generating local deformations and stresses. This technique, referred to as microrheology, links the bulk rheology of fluids to the microscopic dynamics at the particle scale. If tracers are subjected to external forces, rather than freely diffusing, it is called active microrheology. Motivated by the impact of microrheology in providing information on local structure in complex systems such as colloidal glasses, active matter or biological systems, we have extended the dynamic Monte Carlo (DMC) technique to investigate active microrheology in colloidal suspensions. The original DMC theoretical framework, able to accurately describe the Brownian dynamics of colloids at equilibrium, is here reconsidered and expanded to describe the effects of an external force pulling a tracer embedded in isotropic colloidal suspensions at different densities. To this end, we studied the dynamics of a spherical tracer dragged by a constant external force through a bath of spherical and rod-like particles of comparable size. We could extract valuable details on its effective friction coefficient, being constant at small and large values of the external force, but otherwise displaying a nonlinear behaviour that indicates the occurrence of a force-thinning regime. Our DMC simulation results are in excellent quantitative agreement with past Langevin dynamics simulations and theoretical works for the bath of spherical colloids. The bath of rod-like particles is studied in the isotropic phase, and displays an example where DMC is more convenient than Brownian or Langevin dynamics, in this case in dealing with particle rotation
Realistic Utility Functions Prove Difficult for State-of-the-Art Interactive Multiobjective Optimization Algorithms
No full textImprovements to the design of interactive Evolutionary Multiobjective Algorithms (iEMOAs) are unlikely without quantitative assessment of their behaviour in realistic settings. Experiments with human decision-makers (DMs) are of limited scope due to the difficulty of isolating individual biases and replicating the experiment with enough subjects, and enough times, to obtain confidence in the results. Simulation studies may help to overcome these issues, but they require the use of realistic simulations of decision-makers. Machine decision-makers (MDMs) provide a way to carry out such simulation studies, however, studies so far have relied on simple utility functions. In this paper, we analyse and compare two state-of-the-art iEMOAs by means of a MDM that uses a sigmoid-shaped utility function. This sigmoid utility function is based on psychologically realistic models from behavioural economics, and replicates several realistic human behaviours. Our findings are that, on a variety of well-known benchmarks with two and three objectives, the two iEMOAs do not consistently recover the most-preferred points. We hope that these findings provide an impetus for more directed design and analysis of future iEMOAs