Oxygen Vacancy Relaxation and Domain Wall Hysteresis Motion in Cobalt-Doped Barium Titanate Ceramics

Mechanical and dielectric loss measurements were carried out in the BaTiO₃ ceramics doped with Co at frequencies between 0.01 Hz and 1 MHz as a function of temperature from −150° to 150°C. The relaxation peak observed in the ferroelectric phase with an activation energy of 0.27 eV is assumed to be related to the motion of oxygen vacancies. This peak could be because of the reorientation of an electrical dipole made of oxygen vacancies and Co³⁺ ions in the lattice. Furthermore, another loss peak located just below the Curie temperature T _c could be interpreted as hysteretic motion of the domain walls in a regime where the domain wall density is changing.     

Direct ink writing of macroporous lead-free piezoelectric Ba0.85Ca0.15Zr0.1Ti0.9O3

Direct ink writing (DIW) has become a widespread additive manufacturing technique for material engineering, but its application in lead-free Ba_0.85Ca_0.15Zr_0.1Ti_0.9O₃ piezoelectric ceramics from aqueous systems has not been reported so far to our knowledge. The main obstacle is the high extent of hydrolysis reactions undergone by the starting powders when dispersed in water, hindering the attainment of stable water-based colloidal suspensions. This paper reports on the preparation of stable aqueous inks from a deagglomerated and surface-treated powder synthesized by solid-state reaction and on DIW of macroporous lead-free piezoelectrics. Based on zeta potential and rheological measurements, the optimal amounts of processing additives (dispersant, binder, and coagulating agent) were selected to transform the initial fluid suspension to a viscoelastic paste with sufficient stiffness and stability for the printing process. Dielectric and piezoelectric properties of samples sintered under different temperatures were also investigated.     

Performance of administrators, professionals, and paraprofessionals during community-based brain injury rehabilitation training

OBJECTIVE: Two related studies that evaluated the impact of a continuing education program about community-based rehabilitation on the performance of administrators, professionals, and paraprofessionals are presented. One study contained a second part that examined whether differences between pre-course test performance and post-course test performance might be accounted for by practice effects. DESIGN: Factorial mixed model designs. SETTING: University classroom. PARTICIPANTS: Three hundred and eight professionals, administrators, and paraprofessionals from a variety of community-based rehabilitation programs. INTERVENTION: The 4-day graduate-level course focused on three content areas: brain and behavior relationships, behavioral and cognitive intervention strategies, and a rehabilitation philosophy that emphasizes individual client rights. MAIN OUTCOME MEASURE: An examination completed before and immediately after taking the course. RESULTS: Professionals and administrators perform better than paraprofessionals when tested at the beginning and end of the training. However, the absolute differences among these groups were not substantial. In addition, the rate of learning course content was the same for administrators, paraprofessionals, and professionals. CONCLUSIONS: The results support the usefulness of training for all levels of staff and suggest that all levels of staff benefit in an equal fashion.     

Microglial Cell Activation Increases Saturated and Decreases Monounsaturated Fatty Acid Content,but Both Lipid Species are Proinflammatory

Neuroinflammation is a component of age-related neurodegenerative diseases and cognitive decline. Saturated (SFA) and monounsaturated (MUFA) fatty acids are bioactive molecules that may play different extrinsic and intrinsic roles in neuroinflammation, serving as exogenous ligands for cellular receptors, or endogenous components of cell structural, energetic and signaling pathways. We determined the fatty acyl profile of BV2 microglial cells before and after acute activation with lipopolysaccharide (LPS). We also investigated the effect of SFA and MUFA pretreatment on the production of an invasive, neurotoxic phenotype in BV2 cells. Acute activation of BV2 microglia resulted in an increase in the relative content of SFA (12:0, 16:0, 18:0, 20:0, 22:0, and 24:0 increased significantly), and a relative decrease in the content of MUFA (16:1n7, 18:1n7, 18:1n9, 20:1n9, 24:1n9 decreased significantly). In agreement, the major stearoyl-CoA desaturase (SCD) isoform in BV2 cells, SCD2, was significantly down-regulated by LPS. We next treated cells with SFA (16:0 or 18:0) or MUFA (16:1n7 or 18:1n9), and found that levels of secreted IL6 were increased, as was secreted MMP9-mediated proteolytic activity. To test the functional significance, we treated SH-SY5Y neuronal cells with conditioned medium from BV2 cells pretreated with fatty acids, and found a small but significant induction of cell death. Our findings suggest differential intrinsic roles for SFA and MUFA in activated microglial cells, but similar extrinsic roles for these fatty acid species in inducing activation. Expansion of SFA is important during microglial cell activation, but either supplemental SFA or MUFA may contribute to chronic low-grade neuroinflammation.     

A phase diagram of Ba1‐xCaxTiO3 (x = 0‐0.30) piezoceramics by Raman spectroscopy

Piezoelectric ceramics are widely used in sensors, actuators, and ultrasonic transducers due to their ability to achieve efficient conversion between electric and mechanical energy. There is a current drive toward lead‐free material systems capable of achieving comparable piezoelectric performance to environmentally hazardous, but commonly used, lead‐based materials such as lead zirconate titanate. This work constructs an accurate phase diagram for barium calcium titanate (Ba_1‐xCa_xTiO₃ or BCTO). The substitution of Ca²⁺ on the Ba‐site of BCTO is of much interest due to electric property improvements compared to BaTiO₃. In this work, Ba_1‐xCa_xTiO₃ (x = 0‐0.30) samples have been made by solid‐state methods and, following initial characterization by X‐ray diffraction (XRD), evaluation of changes in the Raman spectra has allowed accurate determination of the phase transition temperatures and the construction of a phase diagram.     

Comparison of PMMA and SU-8 resist moulds for embossing of PZT to produce high-aspect-ratio microstructures using LIGA process

 In this paper results are presented from a range of experiments to explore the feasibility of inserting a ceramic material PZT (lead zirconium titanate) into different kinds of high-aspect-ratio resist moulds. Polymethylmethacrylate (PMMA) and SU-8 on silicon substrates and free-standing SU-8 membranes with micro-cavities or through-holes (defined by X-ray lithography) have been used as moulding medium. Processing conditions for the resist materials including pre-bake, exposure, post-bake, development and stripping have been compared. The advantages of different types of resist mould for the LIGA process has been evaluated. Additionally a comparison of photosensitivity of PMMA and SU-8 has been carried out. Using a range of load pressures (5 to 60 MPa), appropriate conditions for PZT embossing into resist moulds have been determined (ensuring minimum void formation in the final PZT structures). In the final form, SU-8 moulds have been removed by laser ablation. This is the first reporting of high-aspect-ratio ceramic microstructures fabricated using a combination of SU-8 moulds and PZT embossing. Received: 10 August 2001/Accepted: 24 September 2001     

High-capacity superconducting current leads of Y1Ba2Cu3O7−x

We have fabricated and measured a high-capacity superconducting current lead composed of a Y₁Ba₂Cu₃O_7?x cylinder, 20 cm long and 0.9 cm² cross section. A steady-state, d.c., critical current of 225 A at a temperature of 77 K was measured in this sample, using a voltage criterion of 2×10^?7 V/cm (p = 8×10^?10 ohm-cm). This current was limited by the currentinduced, self magnetic field. To our knowledge this is the largest d.c. critical current so far reported in a Y₁Ba₂Cu₃O_7?x sample and demonstrates the possibility of using hightemperature superconducting HTS materials for current leads to low-temperature superconducting LTS magnets or in power distribution systems.     

A study into the feasibility of an intelligent knowledge based system (IKBS) in computational fluid mechanics (CFM)

Recently, the emergence of powerful microcomputers has brought comprehensive CFM within the reach of small companies. Consequently, numerical techniques for design and development are becoming cost-effective compared to the increasingly-expensive experimental approach. However, computational fluid modelling of realistic situations is highly complex and requires specialist expertise. The level of complexity is reflected in a leading CFM package, PHOENICS, which is used for the simulation of fluid flow, heat/mass transfer and chemical reaction processes. To successfully apply PHOENICS to a specific problem, specialist knowledge of data input, reasoning adopted by the software, the physics involved and the interpretation of results is essential. This work assesses the feasibility of developing an IKBS to assist and train users with the problem specification process within PHOENICS. An evaluation of a suitable IKBS tool and hardware requirements is included in the assessment.