Stability of the Minimum Energy Path

The minimum energy path (MEP) is the most probable transition path that connects two equilibrium states of a potential energy landscape. It has been widely used to study transition mechanisms as well as transition rates in the fields of chemistry, physics, and materials science. % In this paper, we derive a novel result establishing the stability of MEPs under perturbations of the energy landscape. The result also represents a crucial step towards studying the convergence of numerical discretisations of MEPs

A SIMPLE Approach to Provably Reconstruct Ising Model with Global Optimality

Reconstruction of interaction network between random events is a critical problem arising from statistical physics and politics to sociology, biology, and psychology, and beyond. The Ising model lays the foundation for this reconstruction process, but finding the underlying Ising model from the least amount of observed samples in a computationally efficient manner has been historically challenging for half a century. By using the idea of sparsity learning, we present a approach named SIMPLE that has a dominant sample complexity from theoretical limit. Furthermore, a tuning-free algorithm is developed to give a statistically consistent solution of SIMPLE in polynomial time with high probability. On extensive benchmarked cases, the SIMPLE approach provably reconstructs underlying Ising models with global optimality. The application on the U.S. senators voting in the last six congresses reveals that both the Republicans and Democrats noticeably assemble in each congresses; interestingly, the assembling of Democrats is particularly pronounced in the latest congress

Assessing the Multiple Impacts of Extreme Hurricanes in Southern New England, USA

The southern New England coast of the United States is particularly vulnerable to land-falling hurricanes because of its east-west orientation. The impact of two major hurricanes on the city of Providence (Rhode Island, USA) during the middle decades of the 20th century spurred the construction of the Fox Point Hurricane Barrier (FPHB) to protect the city from storm surge flooding. Although the Rhode Island/Narragansett Bay area has not experienced a major hurricane for several decades, increased coastal development along with potentially increased hurricane activity associated with climate change motivates an assessment of the impacts of a major hurricane on the region. The ocean/estuary response to an extreme hurricane is simulated using a high-resolution implementation of the ADvanced CIRCulation (ADCIRC) model coupled to the Precipitation-Runoff Modeling System (PRMS). The storm surge response in ADCIRC is first verified with a simulation of a historical hurricane that made landfall in southern New England. The storm surge and the hydrological models are then forced with winds and rainfall from a hypothetical hurricane dubbed “Rhody”, which has many of the characteristics of historical storms that have impacted the region. Rhody makes landfall just west of Narragansett Bay, and after passing north of the Bay, executes a loop to the east and the south before making a second landfall. Results are presented for three versions of Rhody, varying in the maximum wind speed at landfall. The storm surge resulting from the strongest Rhody version (weak Saffir–Simpson category five) during the first landfall exceeds 7 m in height in Providence at the north end of the Bay. This exceeds the height of the FPHB, resulting in flooding in Providence. A simulation including river inflow computed from the runoff model indicates that if the Barrier remains closed and its pumps fail (for example, because of a power outage or equipment failure), severe flooding occurs north of the FPHB due to impoundment of the river inflow. These results show that northern Narragansett Bay could be particularly vulnerable to both storm surge and rainfall-driven flooding, especially if the FPHB suffers a power outage. They also demonstrate that, for wind-driven storm surge alone under present sea level conditions, the FPHB will protect Providence for hurricanes less intense than category five

Solutions for control point coordinates and librations for the Saturnian satellite Dione: A simulation based on synthetic data

We explore the application of the Inertial Frame Bundle Block Adjustment (IFBBA) to determine the shape and rotation state of small bodies, e.g., asteroids and natural satellites, using images acquired by spacecraft. Within this particular block adjustment implementation control point (CP) coordinates are tied to the body frame, while the camera parameters and the body’s rotation state use a parameterization, referenced to the inertial frame (Burmeister et al., 2018). The flexibility is especially desirable for objects exhibiting notable (but poorly known) rotational variability, which often requires elaborate formulation depending on the regulating mechanisms. Here we present a full simulation case, based on synthetic data for the Saturnian satellite, Dione. First, we studied the orbital characteristics of the satellite and computed the forcing terms for the longitudinal libration using a frequency analysis approach. We focus on the libration terms connected to the orbital period of 2.739 days and a long-period term of 11 years related to the resonance with Enceladus. We select around 1000 images of Dione collected by the Imaging Science Subsystem onboard the Cassini spaceprobe. Using a recent shape model by Gaskell et al. (2018), we establish a network of CPs with a more or less complete surface coverage. Image coordinates of the CPs are simulated for the observing geometries and orientations of Dione at the given epochs of the images and are taken as observables in the adjustment. We test and extend the functionality of the IFBBA, previously applied to the Martian satellite Phobos and the asteroid 4 Vesta (Burmeister et al., 2018), to the present case. We analyze the estimation errors of the camera parameters, CP coordinates, and in particular, the retrieval of the libration amplitude for Dione. The outcome is expected to be instructive to the real data analysis in the future and shed light on the generalizability of the IFBBA software for other Solar System objects

Enhanced piezoelectric performance of Cr/Ta non-equivalent co-doped Bi4Ti3O12-based high-temperature piezoceramics

In this study, (Cr1/3/Ta2/3) non-equivalent co-doped Bi4Ti3O12 (BIT) ceramics were prepared to solve the problem that high piezoelectric performance, high Curie temperature, and high-temperature resistivity could not be achieved simultaneously in BIT-based ceramics. A series of Bi4Ti3−x(Cr1/3Ta2/3)xO12 (x = 0–0.04) ceramics were synthesized by the solid-state reaction method. The phase structure, microstructure, piezoelectric performance, and conductive mechanism of the samples were systematically investigated. The B-site non-equivalent co-doping strategy combining high-valence Ta5+ and low-valence Cr3+ significantly enhances electrical properties due to a decrease in oxygen vacancy concentration. Bi4Ti2.97(Cr1/3Ta2/3)0.03O12 ceramics exhibit a high piezoelectric coefficient (d33 = 26 pC·N−1) and a high Curie temperature (TC = 687 ℃). Moreover, the significantly increased resistivity (ρ = 2.8×106 Ω·cm at 500 ℃) and good piezoelectric stability up to 600 ℃ are also obtained for this composition. All the results demonstrate that Cr/Ta co-doped BIT-based ceramics have great potential to be applied in high-temperature piezoelectric applications