Origin of the large phonon band-gap in SrTiO3 and the vibrational signatures of ferroelectricity in ATiO3 perovskite: First principles lattice dynamics and inelastic neutron scattering of PbTiO3, BaTiO3 and SrTiO3

We report first principles density functional perturbation theory calculations and inelastic neutron scattering measurements of the phonon density of states, dispersion relations and electromechanical response of PbTiO3, BaTiO3 and SrTiO3. The phonon density-of-states of the quantum paraelectric SrTiO3 is found to be fundamentally distinct from that of ferroelectric PbTiO3 and BaTiO3 with a large 70-90 meV phonon band-gap. The phonon dispersion and electromechanical response of PbTiO3 reveal giant anisotropies. The interplay of covalent bonding and ferroelectricity, strongly modulates the electromechanical response and give rise to spectacular signatures in the phonon spectra. The computed charge densities have been used to study the bonding in these perovskites. Distinct bonding characteristics in the ferroelectric and paraelectric phases give rise to spectacular vibrational signatures. While a large phonon band-gap in ATiO3 perovskites seems a characteristic of quantum paraelectrics, anisotropy of the phonon spectra correlates well with ferroelectric strength. These correlations between the phonon spectra and ferroelectricity, can guide future efforts at custom designing still more effective piezoelectrics for applications. These results suggest that vibrational spectroscopy can help design novel materials.Comment: 11 pages, 4 color figures and 2 Table

Advances in Lead-Free Piezoelectric Materials for Sensors and Actuators

Piezoelectrics have widespread use in today’s sensor and actuator technologies. However, most commercially available piezoelectric materials, e.g., Pb [ZrxTi1−x] O3 (PZT), are comprised of more than 60 weight percent lead (Pb). Due to its harmful effects, there is a strong impetus to identify new lead-free replacement materials with comparable properties to those of PZT. This review highlights recent developments in several lead-free piezoelectric materials including BaTiO3, Na0.5Bi0.5TiO3, K0.5Bi0.5TiO3, Na0.5K0.5NbO3, and their solid solutions. The factors that contribute to strong piezoelectric behavior are described and a summary of the properties for the various systems is provided

AEGIS platforms: using KVA analysis to assess Open Architecture in sustaining engineering

Acquisition research (Graduate School of Business & Public Policy)The purpose of this thesis is to estimate the potential performance improvement in sustaining engineering (SE) when an Open Architecture (OA) approach to system development is used. Its basis is that in Integrated Warfare Systems (IWS) acquisition, 80% of total lifecycle costs occur during the Operation and Support phase. This statistic demonstrates the necessity of measuring how the OA approach will affect software upgrades and maintenance processes for the AEGIS IWS lifecycle. Using the OA approach, advances in distance support and monitoring and maintenance-free operating periods are possible; these advances are significant in supporting the need to reduce costs and manpower while improving performance. To estimate the potential (Return on Investment) ROI that an OA approach might enable SE in the form of software maintenance and upgrades, this thesis will apply the Knowledge Value Added (KVA) methodology to establish the baseline, As Is, configuration of the current solutions in AEGIS. The KVA analysis will yield the ROI's and the current models for the approach to software maintenance and upgrades. Based on the assumptions of OA design for original system development, new approaches to distance and maintenance and monitoring will be explored in To Be solutions, and the ROIs will be estimated. The To Be solutions are rooted in the assumptions of MFOP and ARCI, and the results indicate that these solutions yield a potential improvement of 720% and a cost savings of $3 65,104.63 over the current methodology for just one ship. For all ships using AEGIS, ROI improves by 71,967$2 6,543,824.56. The conclusion is that OA enables extension of these best practice approaches to AEGIS maintenance and upgrade solutions.Approved for public release; distribution is unlimited

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AEGIS platforms using KVA analysis to assess Open Architecture in sustaining engineering

The purpose of this thesis is to estimate the potential performance improvement in sustaining engineering (SE) when an Open Architecture (OA) approach to system development is used. Its basis is that in Integrated Warfare Systems (IWS) acquisition, 80% of total lifecycle costs occur during the Operation and Support phase. This statistic demonstrates the necessity of measuring how the OA approach will affect software upgrades and maintenance processes for the AEGIS IWS lifecycle. Using the OA approach, advances in distance support and monitoring and maintenance-free operating periods are possible; these advances are significant in supporting the need to reduce costs and manpower while improving performance. To estimate the potential (Return on Investment) ROI that an OA approach might enable SE in the form of software maintenance and upgrades, this thesis will apply the Knowledge Value Added (KVA) methodology to establish the baseline, "As Is," configuration of the current solutions in AEGIS. The KVA analysis will yield the ROI's and the current models for the approach to software maintenance and upgrades. Based on the assumptions of OA design for original system development, new approaches to distance and maintenance and monitoring will be explored in "To Be" solutions, and the ROIs will be estimated. The "To Be" solutions are rooted in the assumptions of MFOP and ARCI, and the results indicate that these solutions yield a potential improvement of 720% and a cost savings of $3 65,104.63 over the current methodology for just one ship. For all ships using AEGIS, ROI improves by 71,967$2 6,543,824.56. The conclusion is that OA enables extension of these best practice approaches to AEGIS maintenance and upgrade solutions.http://archive.org/details/aegisplatformsus109452987Approved for public release; distribution is unlimited

Design Models for the Development of Helium-Carbon Sorption Crycoolers

We have developed models for predicting the performance of helium-based Joule-Thomson continuous-flow cryocoolers using charcoal-pumped sorption compressors. The models take as inputs the number of compressors, desired heat-lift, cold tip temperature, and available precooling temperature and provide design parameters as outputs. Future laboratory development will be used to verify and improve the models. We will present a preliminary design for a two-stage vibration-free cryocooler that is being proposed as part of a mid-infrared camera on NASA's Next Generation Space Telescope. Model predictions show that a 10 mW helium-carbon cryocooler with a base temperature of 5.5 K will reject less than 650 mW at 18 K. The total input power to the helium-carbon stage is 650 mW. These models, which run in MathCad and Microsoft Excel, can be coupled to similar models for hydrogen sorption coolers to give designs for 2-stage vibration-free cryocoolers that provide cooling from approx. 50 K to 4 K