Rocchio's relevance feedback model is a classic query expansion method and it has been shown to be effective in boosting information retrieval performance. The selection of expansion terms in this method, however, does not take into account the relationship between the candidate terms and the query terms (e.g., term proximity). Intuitively, the proximity between candidate expansion terms and query terms can be exploited in the process of query expansion, since terms closer to query terms are more likely to be related to the query topic.In this paper, we study how to incorporate proximity information into the Rocchio's model, and propose a proximitybased Rocchio's model, called PRoc, with three variants. In our PRoc models, a new concept (proximity-based term frequency, ptf ) is introduced to model the proximity information in the pseudo relevant documents, which is then used in three kinds of proximity measures. Experimental results on TREC collections show that our proposed PRoc models are effective and generally superior to the state-of-the-art relevance feedback models with optimal parameters. A direct comparison with positional relevance model (PRM) on the GOV2 collection also indicates our proposed model is at least competitive to the most recent progress.

The spin Hall magnetoresistance (SMR) effect is studied in a magnetoelectric Cr2O3/heavy-metal W heterostructure. The Cr2O3 film is confirmed as the α-phase, and its Néel temperature is determined. A clear SMR behavior is observed at the interface of Cr2O3/W. A nearly 0.1% SMR ratio is achieved under a magnetic field of 9 T, which is larger than the reported value in the SrMnO3/Pt structure. A systematic study on the variations of SMR as functions of the magnetic field and its angle is performed. Our results indicate that the antiferromagnetic magnetoelectric Cr2O3/W structure has a promising prospect application in future spintronic devices.

We investigate the observation of negative spin Hall magnetoresistance (SMR) in antiferromagnetic Cr2O3/Ta bilayers at low temperature. The sign of the SMR signals is changed from positive to negative monotonously from 300 K to 50 K. The change of the signs for SMR is related with the competitions between the surface ferromagnetism and bulky antiferromagnetic of Cr2O3. The surface magnetizations of α-Cr2O3 (0001) is considered to be dominated at higher temperature, while the bulky antiferromagnetics gets to be robust with decreasing of temperature. The slopes of the abnormal Hall curves coincide with the signs of SMR, confirming variational interface magnetism of Cr2O3 at different temperature. From the observed SMR ratio under 3 T, the spin mixing conductance at Cr2O3/Ta interface is estimated to be 1.12 × 10 14 Ω -1 · m -2 , which is comparable to that of YIG/Pt structures and our early results of Cr2O3/W. (Appl. Phys.Lett. 110, 262401 (2017)) a) Electronic

Sodium bismuth titanate (Na0.5Bi0.5)TiO3 (NBT) of perovskite structure is among the best known lead-free piezoelectric∕ferroelectric that promises a number of applications in sensors and actuators. However, NBT in thin film form has not been properly investigated, although NBT in bulk ceramic form has been widely studied. In this letter, we report the growth of polycrystalline NBT thin films by radio-frequency magnetron sputtering and their ferroelectric behavior. The NBT thin films exhibit a well-defined hysteresis loop, with a remanent polarization of 11.9μC∕cm2 and coercive field of 37.9kV∕cm when measured at room temperature. There is a steady decrease of dielectric constant in the range of 650–470 over the frequency range of 10–105Hz. A change in the controlling mechanism of electrical behavior from the grain interior to the grain boundary is observed for the NBT thin film with increasing temperature. Hopping of oxygen vacancies trapped at the grain boundaries is responsible for the high dielectric loss at low frequencies and high dc conductivity observed.

Pt /( Ba 0.7 Sr 0.3 ) TiO 3  (BST)/YBa2Cu3O7−x capacitors were prepared and investigated for the dead-layer (DL) thickness (td) and the DL dielectric constant (εd). Based on the series capacitor model, the td/εd ratio of 0.066 nm and the bulk BST ferroelectric-layer dielectric constant of 1370 were obtained through the measurements of the capacitance–voltage characteristics. The td×εd value of 120 nm was obtained through the measurements of the current–voltage characteristics. Combining these data, the DL thickness and the DL dielectric constant are respectively estimated to be 2.8 nm and 42.6.