Atomic-scale observations of electrical and mechanical manipulation of topological polar flux closure

The ability to controllably manipulate complex topological polar configurations such as polar flux-closures via external stimuli may allow the construction of new electromechanical and nanoelectronic devices. Here, using atomically resolved in situ scanning transmission electron microscopy, we find that the polar flux-closures in PbTiO3/SrTiO3superlattice films are mobile and can be reversibly switched to ordinary single ferroelectriccoradomains under an applied electric field or stress. Specifically, the electric field initially drives movement of a flux-closure via domain wall motion and then breaks it to form intermediatea/cstriped domains, whereas mechanical stress first squeezes the core of a flux-closure toward the interface and then forma/cdomains with disappearance of the core. After removal of the external stimulus, the flux-closure structure spontaneously recovers. These observations can be precisely reproduced by phase field simulations, which also reveal the evolutions of the competing energies during phase transitions. Such reversible switching between flux-closures and ordinary ferroelectric states provides a foundation for potential electromechanical and nanoelectronic applications.

Power-law Distribution Aware Trust Prediction

Trust prediction, aiming to predict the trust relations between users in a social network, is a key to helping users discover the reliable information. Many trust prediction methods are proposed based on the low-rank assumption of a trust network. However, one typical property of the trust network is that the trust relations follow the power-law distribution, i.e., few users are trusted by many other users, while most tail users have few trustors. Due to these tail users, the fundamental low-rank assumption made by existing methods is seriously violated and becomes unrealistic. In this paper, we propose a simple yet effective method to address the problem of the violated low-rank assumption. Instead of discovering the low-rank component of the trust network alone, we learn a sparse component of the trust network to describe the tail users simultaneously. With both of the learned low-rank and sparse components, the trust relations in the whole network can be better captured. Moreover, the transitive closure structure of the trust relations is also integrated into our model. We then derive an effective iterative algorithm to infer the parameters of our model, along with the proof of correctness. Extensive experimental results on real-world trust networks demonstrate the superior performance of our proposed method over the state-of-the-arts.

Generated designs: Structure and composition

Generated designs are formed through rules that change, and structures that interpret, descriptions. The structure of design descriptions is examined with particular reference to generative shape descriptions acting as the infrastructure for attributes. Structure is represented by relations among the parts of descriptions. In particular, a closure structure allows relations to be described by the parts themselves. Design processes use descriptions in combination. It is shown how to combine separate descriptions in parallel and sequentially. Rules change descriptions. It is shown how to aggregate local changes consistently across a design and to use rules with structure on their component shapes to highlight selected emergent features. Further, multiple attribute descriptions, including shape and associated properties, are constructed. Their structures are represented algebraically.

The Structure of Designs

The role of design descriptions is reviewed particularly in providing connections between product and process. The relations among the parts of descriptions represent the structure of designs. We consider the particular case when the parts form a closure structure and derive conclusions about the topology of descriptions. Following the scheme adopted for shapes and shape grammars we show that closure structures are a direct consequence of the primary role of relations in descriptions. Design processes use descriptions both individually and in combination. The different descriptions of a design display a partial order. It is shown how to combine descriptions into new descriptions. Further, multiple attribute descriptions including, for example, shape and associated properties, are constructed. Their structures are represented algebraically.

DESIGN OF ENCLOSED HARBORS TO REDUCE SEDIMENTATION

Sedimentation may be an important problem when quantities of suspended material are carried into an enclosed harbor on a flooding tide. In order to forecast future maintenance costs, two methods for predicting the sedimentation rate prior to harbor construction are proposed: 1) a sedimentation tank to be placed at the proposed harbor site, and 2) a mathematical model which uses sediment and hydraulic data collected at the harbor site. Certain considerations in the design phase of a project may effect a reduction in harbor sedimentation. If feasible, the harbor may be sited in a region where suspended sediment concentrations are low and sediment sizes (settling velocities) are small. Proximity to river sediment sources may be a factor. Conversely, a harbor site in a clear-water river adjacent to a sediment-laden estuary may be desirable if bedload transport during freshets would not be a problem. Settlement of suspended material may occur in the channel which connects an enclosed harbor basin with navigable waters. This material may subsequently be resuspended and carried into the basin thereby increasing the sedimentation rate. To reduce that rate the channel should be designed as short as possible. A sill in the channel may also be used to reduce initial excavation costs and the sedimentation rate. Flotation for vessels in the basin will be provided at all times, but movement into and out of the harbor will be reduced to times of higher water. In high latitude areas where harbor use is limited to periods when ice cover is absent, the sedimentation rate may be reduced using a channel closure structure during non-use periods. Winter sedimentation rates can be predicted using the mathematical model for summer conditions, and when ice thickness is known.