University of Waterloo

About: University of Waterloo is a education organization based out in Waterloo, Ontario, Canada. It is known for research contribution in the topics: Population & Context (language use). The organization has 36093 authors who have published 93906 publications receiving 2948139 citations. The organization is also known as: UW & uwaterloo.

Extra storage capacity in transition metal oxide lithium-ion batteries revealed by in situ magnetometry.

Abstract: In lithium-ion batteries (LIBs), many promising electrodes that are based on transition metal oxides exhibit anomalously high storage capacities beyond their theoretical values. Although this phenomenon has been widely reported, the underlying physicochemical mechanism in such materials remains elusive and is still a matter of debate. In this work, we use in situ magnetometry to demonstrate the existence of strong surface capacitance on metal nanoparticles, and to show that a large number of spin-polarized electrons can be stored in the already-reduced metallic nanoparticles (that are formed during discharge at low potentials in transition metal oxide LIBs), which is consistent with a space charge mechanism. Through quantification of the surface capacitance by the variation in magnetism, we further show that this charge capacity of the surface is the dominant source of the extra capacity in the Fe3O4/Li model system, and that it also exists in CoO, NiO, FeF2 and Fe2N systems. The space charge mechanism revealed by in situ magnetometry can therefore be generalized to a broad range of transition metal compounds for which a large electron density of states is accessible, and provides pivotal guidance for creating advanced energy storage systems.

Autonomic control of heart rate during exercise studied by heart rate variability spectral analysis.

Abstract: Spectral analysis of heart rate variability (HRV) might provide an index of relative sympathetic (SNS) and parasympathetic nervous system (PNS) activity during exercise. Eight subjects completed si...

Efficient Measurement of Quantum Gate Error by Interleaved Randomized Benchmarking

Abstract: We describe a scalable experimental protocol for estimating the average error of individual quantum computational gates. This protocol consists of interleaving random Clifford gates between the gate of interest and provides an estimate as well as theoretical bounds for the average error of the gate under test, so long as the average noise variation over all Clifford gates is small. This technique takes into account both state preparation and measurement errors and is scalable in the number of qubits. We apply this protocol to a superconducting qubit system and find a bounded average error of 0.003 [0,0.016] for the single-qubit gates ${X}_{\ensuremath{\pi}/2}$ and ${Y}_{\ensuremath{\pi}/2}$. These bounded values provide better estimates of the average error than those extracted via quantum process tomography.

A Field Exercise on Groundwater Flow Using Seepage Meters and Mini-piezometers

Abstract: Basic principles of physical hydrogeology and the nature of the hydrologic interactions between groundwater and surface water can be convincingly demonstrated in the field using two inexpensive and...

Experiences extended across time: Evaluation of moments and episodes

Abstract: Intuitions relating to outcomes extended over time are examined. Utility integration is proposed as a normative rule for the evaluation of extended episodes. In Experiment 1, subjects explicitly compared aversive experiences of varying durations. By several measures, disutility was a marginally decreasing function of episode duration, even for experiences that were thought to become increasingly aversive. This pattern is a qualitative violation of the integration rule. In Experiment 2, subjects made global evaluations of a hypothetical person's aversive experiences, on the basis of a series of subjective ratings of discomfort made at periodic intervals. The results showed an extreme sensitivity to improving or deteriorating trend and a striking neglect of duration. The final moments of an extended episode appear to exert a strong influence on the overall judgment. This leads to violations of monotonicity when adding some moments of moderate pain reduces judgments of global aversiveness.