First-Principles Modeling of Pt/LaAlO3/SrTiO3 Capacitors Under an External Bias Potential

We study the electrical properties of Pt/LaAlO3/SrTiO3 capacitors under the action of an external bias potential, using first-principles simulations performed at constrained electric displacement field. A complete set of band diagrams, together with the relevant electrical characteristics (capacitance and built-in fields), are determined as a function of LaAlO3 thickness and the applied potential.We find that the internal field in LaAlO3 monotonically decreases with increasing thickness; hence, the occurrence of spontaneous Zener tunneling is ruled out in this system.We discuss the implications of our results in the light of recent experimental observations on biased LaAlO3/SrTiO3 junctions involving metallic top electrodes.Comment: 5 pages, 4 figure

A Review of \u3cem\u3eTeaching as a Moral Practice: Defining, Developing, and Assessing Professional Dispositions in Teacher Education\u3c/em\u3e

A review of the book Teaching as a Moral Practice: Defining, Developing, and Assessing Professional Dispositions in Teacher Education, by Peter C. Murrell Jr., Mary Diez, Sharon Feiman-Nemser, and Deborah L. Schussler (Harvard University Press, 2010)

The Wisdom of Practice Meets the Pursuit of Scientific Inquiry. A Response to Scientifically Based Research and Teacher Agency: Combating \u27Conspiracies of Certainty\u27

Stemhagen and Nomi argued that the influence of many contemporary forms of education research, especially scientifically based research, inevitably position teachers as problems rather than as active agents whose judgement is indivisible from the activity of teaching and learning. We share the authors’ intuitions and concerns about the divide between research and teaching but also wonder if there remains another way into some of the concerns they raise. We start with a different question but one we think is fundamental to Stemhagen and Nomi’s critique: How do the findings of empirical research make their way into the work of teaching? By answering this question, we hope to reframe the authors’ concerns and reconsider their recommendation that teachers become participatory action researchers. It is distressing that practitioners and researchers have not yet found ways (despite the insights of John Dewey and other theorist and practitioners over more than a century) to substantively account for each others’ growing understanding because both the wisdom of practice and the pursuit of scientific insight are central to the effective and generative practice of educating children and adults

A linear theory for control of non-linear stochastic systems

We address the role of noise and the issue of efficient computation in stochastic optimal control problems. We consider a class of non-linear control problems that can be formulated as a path integral and where the noise plays the role of temperature. The path integral displays symmetry breaking and there exist a critical noise value that separates regimes where optimal control yields qualitatively different solutions. The path integral can be computed efficiently by Monte Carlo integration or by Laplace approximation, and can therefore be used to solve high dimensional stochastic control problems.Comment: 5 pages, 3 figures. Accepted to PR

Integrating Design Thinking in Chemical Engineering Coursework for Enhanced Student Learning

In the engineering discipline, it is of utmost importance to give value to applied learning because as engineers, we are expected to innovate, and innovations happen when theoretical ideas are implemented successfully. Design thinking is one such approach that can enhance the value of theoretical concepts and motivate the students to visualize their ideas in more meaningful ways. The five stages of design thinking include: (i) Empathize, (ii) Define, (iii) Ideate, (iv) Prototype, and (v) Test. The traditional engineering curriculum focuses on the last four stages and thus leads to a skewed perspective among students with regards to problem definition, formulation, and solution. In this proposed curricular modification, we have developed computational modules as part of the Process Optimization and Experimental Methods in Chemical Engineering courses offered to seniors in the chemical engineering department as electives, which encompass all five stages of design thinking

Optimal Control Theory for Continuous Variable Quantum Gates

We apply the methodology of optimal control theory to the problem of implementing quantum gates in continuous variable systems with quadratic Hamiltonians. We demonstrate that it is possible to define a fidelity measure for continuous variable (CV) gate optimization that is devoid of traps, such that the search for optimal control fields using local algorithms will not be hindered. The optimal control of several quantum computing gates, as well as that of algorithms composed of these primitives, is investigated using several typical physical models and compared for discrete and continuous quantum systems. Numerical simulations indicate that the optimization of generic CV quantum gates is inherently more expensive than that of generic discrete variable quantum gates, and that the exact-time controllability of CV systems plays an important role in determining the maximum achievable gate fidelity. The resulting optimal control fields typically display more complicated Fourier spectra that suggest a richer variety of possible control mechanisms. Moreover, the ability to control interactions between qunits is important for delimiting the total control fluence. The comparative ability of current experimental protocols to implement such time-dependent controls may help determine which physical incarnations of CV quantum information processing will be the easiest to implement with optimal fidelity.Comment: 39 pages, 11 figure

Carrier-mediated magnetoelectricity in complex oxide heterostructures

While tremendous success has been achieved to date in creating both single phase and composite magnetoelectric materials, the quintessential electric-field control of magnetism remains elusive. In this work, we demonstrate a linear magnetoelectric effect which arises from a novel carrier-mediated mechanism, and is a universal feature of the interface between a dielectric and a spin-polarized metal. Using first-principles density functional calculations, we illustrate this effect at the SrRuO$_3$/SrTiO$_3$ interface and describe its origin. To formally quantify the magnetic response of such an interface to an applied electric field, we introduce and define the concept of spin capacitance. In addition to its magnetoelectric and spin capacitive behavior, the interface displays a spatial coexistence of magnetism and dielectric polarization suggesting a route to a new type of interfacial multiferroic

Evaluating the diurnal cycle in cloud top temperature from SEVIRI

The variability of convective cloud spans a wide range of temporal and spatial scales and is of fundamental importance for global weather and climate systems. Datasets from geostationary satellite instruments such as the Spinning Enhanced Visible and Infrared Imager (SEVIRI) provide high-time-resolution observations across a large area. In this study we use data from SEVIRI to quantify the diurnal cycle of cloud top temperature within the instrument's field of view and discuss these results in relation to retrieval biases. We evaluate SEVIRI cloud top temperatures from the new CLAAS-2 (CLoud property dAtAset using SEVIRI, Edition 2) dataset against Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP) data. Results show a mean bias of +0.44 K with a standard deviation of 11.7 K, which is in agreement with previous validation studies. Analysis of the spatio-temporal distribution of these errors shows that absolute retrieval biases vary from less than 5 K over the southeast Atlantic Ocean up to 30 K over central Africa at night. Night- and daytime retrieval biases can also differ by up to 30 K in some areas, potentially contributing to biases in the estimated amplitude of the diurnal cycle. This illustrates the importance of considering spatial and diurnal variations in retrieval errors when using the CLAAS-2 dataset. Keeping these biases in mind, we quantify the seasonal, diurnal, and spatial variation of cloud top temperature across SEVIRI's field of view using the CLAAS-2 dataset. By comparing the mean diurnal cycle of cloud top temperature with the retrieval bias, we find that diurnal variations in the retrieval bias can be small but are often of the same order of magnitude as the amplitude of the observed diurnal cycle, indicating that in some regions the diurnal cycle apparent in the observations may be significantly impacted by diurnal variability in the accuracy of the retrieval. We show that the CLAAS-2 dataset can measure the diurnal cycle of cloud tops accurately in regions of stratiform cloud such as the southeast Atlantic Ocean and Europe, where cloud top temperature retrieval biases are small and exhibit limited spatial and temporal variability. Quantifying the diurnal cycle over the tropics and regions of desert is more difficult, as retrieval biases are larger and display significant diurnal variability. CLAAS-2 cloud top temperature data are found to be of limited skill in measuring the diurnal cycle accurately over desert regions. In tropical regions such as central Africa, the diurnal cycle can be described by the CLAAS-2 data to some extent, although retrieval biases appear to reduce the amplitude of the real diurnal cycle of cloud top temperatures. This is the first study to relate the diurnal variations in SEVIRI retrieval bias to observed diurnal cycles in cloud top temperature. Our results may be of interest to those in the observation and modelling communities when using cloud top properties data from SEVIRI, particularly for studies considering the diurnal cycle of convection

Flexoelectricity and the polarity of complex ferroelastic twin patterns

We study, by means of an atomistic toy model, the interplay of ferroelastic twin patterns and electrical polarization. Our molecular dynamics simulations reproduce polarity in straight twin walls as observed experimentally. We show, by making contact with continuum theory, that the effect is governed by linear flexoelectricity. Complex twin patterns, with very high densities of kinks and/or junctions, produce winding structures in the dipolar field, which are reminiscent of polarization vortices. By means of a "cold shearing" technique, we produce patches with high vortex densities; these unexpectedly show a net macroscopic polarization even if neither the original sample nor the applied mechanical perturbation breaks inversion symmetry by itself. These results may explain some puzzling experimental observations of "parasitic" polarity in the paraelectric phase of BaTiO3 and LaAlO3.EKHS is grateful to EPSRC for financial support (EP/K009702/1). SL and PG appreciate the support by Helmholtz Programme Science and Technology of Nanosystems (STN) (Vorhabensnumber 43.22.01). MS acknowledges support by MINECO-Spain through Grants No. FIS2013-48668-C2-2-P and No. SEV-2015-0496, and by Generalitat de Catalunya (2014 SGR301). X.D. appreciates the support of NSFC (51171140, 51231008, 51320105014, 51321003), the 973 Programs of China (2012CB619402), and 111 project (B06025)