A superior piezoelectric coefficient (d = 570 ± 10 pC N ), the highest value reported to date in potassium-sodium niobate-based ceramics, is obtained in (1-x-y)K Na Nb Sb O BaZrO - Bi K HfO ceramics. This high d value can be ascribed to the co-existence of "nano-scale strain domains" (1-2 nm) and a high density of ferroelectric domain boundaries. Therefore, ternary KNN-based ceramics demonstrate the potential for applications.

Conventional x-ray computed tomography (CT) produces a single volumetric image that represents the spatially variant linear x-ray attenuation coefficient of an object. However, in many situations, differences in the x-ray attenuation properties of soft tissues are very small and difficult to measure in conventional x-ray imaging. In this work, we investigate an analyzer-based imaging method, called computed tomography multiple-image radiography (CT-MIR), which is a tomographic implementation of the recently proposed multiple-image radiography method. The CT-MIR method reconstructs concurrently three physical properties of the object. In addition to x-ray attenuation, CT-MIR produces volumetric images that represent the refraction and ultrasmall-angle scattering properties of the object. These three images can provide a rich description of the object's physical properties that are revealed by the probing x-ray beam. An imaging model for CT-MIR that is based on the x-ray transform of the object properties is established. The CT-MIR method is demonstrated by use of experimental data acquired at a synchroton radiation imaging beamline, and is compared to the pre-existing diffraction-enhanced imaging CT method. We also investigate the merit of an iterative reconstruction method for use with future clinical implementations of CT-MIR, which we anticipate would be photon limited.

Abstract. The database-as-a-service (DAS) model is a newly emerging computing paradigm, where the DBMS functions are outsourced. It is desirable to store data on database servers in encrypted form to reduce security and privacy risks since the server may not be fully trusted. But this usually implies that one has to sacrifice functionality and efficiency for security. Several approaches have been proposed in recent literature for efficiently supporting queries on encrypted databases. These approaches differ from each other in how the index of attribute values is created. Random one-to-one mapping and order-preserving are two examples. In this paper we will adapt a prefix-preserving encryption scheme to create the index. Certainly, all these approaches look for a convenient trade-off between efficiency and security. In this paper we will discuss the security issues and efficiency of these approaches for supporting range queries on encrypted numeric data.

Because of their high toxicity, lead-based materials in electronic devices must be replaced by lead-free piezoelectric materials. However, some issues remain that hinder the industrial applications of these alternative ceramics. Here, we report the construction of a 0-3-type ceramic composite (KNNS-BNKZ: xZnO), where the Sb-doped ZnO submicronic particles were randomly distributed throughout the potassium-sodium niobate-based ceramic matrix. In this (K,Na)NbO (KNN)-based ceramic composite, superior temperature stability, excellent piezoelectric properties, and a high Curie temperature were simultaneously achieved. The unipolar strain varied from +20 to -16% when the temperature was increased from 23 to 200 °C in KNNS-BNKZ: xZnO with x = 0.75. By increasing the ZnO content from x = 0 to x = 5.0, the Curie temperature was increased from 227 to 294 °C. More importantly, the piezoelectric coefficient remained high ( d = 480-510 pC/N) for a wide range of compositions, x = 0.25-1.0. Transmission electron microscopy (TEM) experiments showed that the compensatory electric fields generated by the Sb-doped ZnO submicronic particles were responsible for the improved temperature stability. The high piezoelectricity was due to the existence of nanodomains, which were clearly observed in the TEM experiments. The results presented in this work clarify some of the physical mechanisms in this KNN-based ceramic composite, thus advancing the development of lead-free ceramics.

No abstract

No abstract

Ferroelectric materials under shock compression can generate current and power by a drastic change of the remnant polarizations and surface bound charge. This behavior has been employed in applications involving nuclear fusion trigger, energy storage devices, and high pulse power sources. Despite the large power output in lead-containing ferroelectrics, lead-free materials are highly desirable owing to the environmental concerns. Herein, the phase transition behaviors and current outputs of 0.92Bi 0.5 Na 0.5 TiO 3-0.08BiAlO 3 (BNT-8BA) materials are studied under high pressure. The BNT-8BA ferroelectric ceramics can be completely depolarized from polar to the nonpolar state under shock compression, resulting in a current output in the external circuit. The phase-transition-induced depolarization pressures of BNT-8BA are lower than those of the pure Bi 0.5 Na 0.5 TiO 3 under both dynamic and static high-pressure loads. These results can allow the understanding of the high-pressure behavior of BNT-8BA for application as ferroelectric pulsed power supply.

No abstract