A fundamental assumption in statistical physics is that generic closed quantum many-body systems thermalize under their own dynamics. Recently, the emergence of many-body localized systems has ...questioned this concept and challenged our understanding of the connection between statistical physics and quantum mechanics. Here we report on the observation of a many-body localization transition between thermal and localized phases for bosons in a two-dimensional disordered optical lattice. With our single-site–resolved measurements, we track the relaxation dynamics of an initially prepared out-of-equilibrium density pattern and find strong evidence for a diverging length scale when approaching the localization transition. Our experiments represent a demonstration and in-depth characterization of many-body localization in a regime not accessible with state-of-the-art simulations on classical computers.
Relative permeability measurements from drainage coreflooding experiments are effective properties that vary with injection rate when capillary heterogeneity effects are present. It is therefore ...important to estimate the fine‐scale characteristic relative permeability (
krchar), which is independent of flow rate and can be used for accurate reservoir simulation and numerical modeling of coreflooding. Previous methods for
krchar estimation are based on two‐phase flow simulations with fine‐scale heterogeneous permeability and capillary pressure. These are computationally complex and prone to error. This work presents a reduced method, based on a simplified model, requiring only solutions of steady state single‐phase flow equations. The simplified model is used to study a number of synthetic 2‐D permeability realizations and 3‐D core models constructed based on experimental data from previous literature. The
krchar estimation method is tested on these examples and shown to be generally accurate. Cases where estimation error is significant are characterized by low injection rates, large nonwetting phase fractional flow, strong capillary heterogeneity, and small capillary number (ratio between core average pressure drop and capillary pressure drop). The estimation error is believed to be related to errors in the full‐model (two‐phase flow) simulations; that is, we find that for low injection rates, our simulator presents significantly different results compared to a commercial simulator. This could explain the source of mismatch between full and simplified methods and calls for further investigation of inaccuracy in numerical simulations at low flow rates, which could have implications for coreflood modeling and low rate reservoir simulation.
Key Points
A new method is presented for estimating characteristic relative permeability using reduced equations
The method is validated on 2‐D synthetic data and realistic 3‐D coreflooding data
Any mismatch between the new method and synthetic data is believed to be related to errors in flow simulator
The role of simulation-based education continues to expand exponentially. To excel in this environment as a surgical simulation leader requires unique knowledge, skills, and abilities that are ...different from those used in traditional clinically-based education.
Leaders in surgical simulation were invited to participate as discussants in a pre-conference course offered by the Association for Surgical Education. Highlights from their discussions were recorded.
Recommendations were provided on topics such as building a simulation team, preparing for accreditation requirements, what to ask for during early stages of development, identifying tools and resources needed to meet educational goals, expanding surgical simulation programming, and building educational curricula.
These recommendations provide new leaders in simulation with a unique combination of up-to-date best practices in simulation-based education, as well as valuable advice gained from lessons learned from the personal experiences of national leaders in the field of surgical simulation and education.
The implementation of simulation-based training (SBT) to teach flexible bronchoscopy (FB) skills to novice trainees has increased during the last decade. However, it is unknown whether SBT is ...effective to teach FB to novices and which instructional features contribute to training effectiveness.
How effective is FB SBT and which instructional features contribute to training effectiveness?
We searched Embase, PubMed, Scopus, and Web of Science for articles on FB SBT for novice trainees, considering all available literature until November 10, 2022. We assessed methodological quality of included studies using a modified version of the Medical Education Research Study Quality Instrument, evaluated risk of bias with relevant tools depending on study design, assessed instructional features, and intended to correlate instructional features to outcome measures.
We identified 14 studies from an initial pool of 544 studies. Eleven studies reported positive effects of FB SBT on most of their outcome measures. However, risk of bias was moderate or high in eight studies, and only six studies were of high quality (modified Medical Education Research Study Quality Instrument score ≥ 12.5). Moreover, instructional features and outcome measures varied highly across studies, and only four studies evaluated intervention effects on behavioral outcome measures in the patient setting. All of the simulation training programs in studies with the highest methodological quality and most relevant outcome measures included curriculum integration and a range in task difficulty.
Although most studies reported positive effects of simulation training programs on their outcome measures, definitive conclusions regarding training effectiveness on actual bronchoscopy performance in patients could not be made because of heterogeneity of training features and the sparse evidence of training effectiveness on validated behavioral outcome measures in a patient setting.
PROSPERO; No.: CRD42021262853; URL: https://www.crd.york.ac.uk/prospero/
A new machine learning methodology is proposed for speeding up thermochemistry computations in simulations of turbulent combustion. The approach is suited to a range of methods including Direct ...Numerical Simulation (DNS), Probability Density Function (PDF) methods, unsteady flamelet, Conditional Moment Closure (CMC), Multiple Mapping Closure (MMC), Linear Eddy Model (LEM), Thickened Flame Model, the Partially Stirred Reactor (PaSR) method (as in OpenFOAM) and the computation of laminar flames. In these methods, the chemical source term must be evaluated at every time step, and is often the most expensive element of a simulation. The proposed methodology has two main objectives: to offer enhanced capacity for generalisation and to improve the accuracy of the ANN prediction. To accomplish the first objective, we propose a hybrid flamelet/random data (HFRD) method for generating the training set. The random element endows the resulting ANNs with increased capacity for generalisation. Regarding the second objective, a multiple multilayer perceptron (MMP) approach is developed where different multilayer perceptrons (MLPs) are trained to predict states that result in smaller or larger composition changes, as these states feature different dynamics. It is shown that the multiple MLP method can greatly reduce the prediction error, especially for states yielding small composition changes. The approach is used to simulate flamelets of varying strain rates, one-dimensional premixed flames with differential diffusion and varying equivalence ratio, and finally the Large Eddy Simulation (LES) of CH4/air piloted flames Sandia D, E and F, which feature different levels of local extinction. The simulation results show very good agreement with those obtained from direct integration, while the range of problems simulated indicates that the approach has great capacity for generalisation. Finally, a speed-up ratio of 12 is attained for the reaction step.
ABSTRACT The late stages of terrestrial planet formation are dominated by giant impacts that collectively influence the growth, composition, and habitability of any planets that form. Hitherto, ...numerical models designed to explore these late stage collisions have been limited by assuming that all collisions lead to perfect accretion, and many of these studies lack the large number of realizations needed to account for the chaotic nature of N-body systems. We improve on these limitations by performing 280 simulations of planet formation around a Sun-like star, half of which used an N-body algorithm that has recently been modified to include fragmentation and hit-and-run (bouncing) collisions. We find that when fragmentation is included, the final planets formed are comparable in terms of mass and number; however, their collision histories differ significantly and the accretion time approximately doubles. We explored impacts onto Earth-like planets, which we parameterized in terms of their specific impact energies. Only 15 of our 164 Earth-analogs experienced an impact that was energetic enough to strip an entire atmosphere. To strip about half of an atmosphere requires energies comparable to recent models of the Moon-forming giant impact. Almost all Earth-analogs received at least one impact that met this criteria during the 2 Gyr simulations and the median was three giant impacts. The median time of the final giant impact was 43 Myr after the start of the simulations, leading us to conclude that the time-frame of the Moon-forming impact is typical among planetary systems around Sun-like stars.
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