Free-standing Body Research Articles

Oxygen diffusion in freestanding body centered cubic tantalum structural thin films in air and in high vacuum

Sensors and actuators constructed from freestanding tantalum thin films show promise for micromachining applications and for the study of thin film mechanical behavior. To assess this promise, it is necessary to gain further understanding of the performance of Ta as a structural material. We first evaluate the coefficient of thermal expansion, αTa, using micromachined bent beams, which amplify displacement compared to linear expansion. The value for αTa is 6.8 × 10−6 m/m °C, in good agreement with the bulk value. This validation enables the study of interstitial oxygen diffusion in Ta, for which literature values of activation energy vary widely, from 0.60 to 1.98 eV. Displacement in air due to oxygen diffusion becomes measurable after 30 min exposure at 180 °C. We extract an activation energy for interstitial oxygen in Ta of 0.53 eV/atom. Analysis indicates that lattice rather than grain boundary diffusion is the associated mechanism. To inhibit the oxidation, we construct a thermal stage that controls specimen temperature in 10−5 Pa vacuum. Then, after a 24 h hold, oxidation is suppressed up to 400 °C. This result is discussed in terms of O dissolution from its native oxide, coupled with further absorption from background gases.

Riding the Iron Horse into the Future of Regulation: The Contribution of Charles Francis Adams Jr.

Charles F. Adams Jr. instigated the creation of the Massachusetts Railway Commission in 1869. This freestanding body sought to oversee the overall the operation of railroads in that state. This paper suggests that many of our current ideas about the process and content of commercial regulation were developed in the historical context.

Calculation of the elastic strain energy of inclusions by the Green's function and finite element methods

Elastic strain energy of a free-standing body with many inclusions was calculated. In order to consider the effect of surrounding neighborhood inclusions, nonlocal terms of the Green's function were kept. The calculated strain energy by a derived analytic method was compared with that of the finite element method. The prediction of the new analytic method provided a correct tendency of the variation of the strain energy for various sample problems. Deviation of the analytic result from that of the finite element calculation became smaller when the value of the strain energy decreased. As the analytic method does not require solving the field equations, it can be useful for a situation demanding prompt computation of the strain energy.

Microstructure and Properties of Plasma Sprayed Lead Zirconate Titanate (PZT) Ceramics

Lead zirconate titanate (PZT) was plasma sprayed onto various substrates of different character. Additionally, a free-standing body made by plasma spraying was investigated. X-ray diffraction analyses of a decomposition of the as-sprayed coating products detected components of the PT-PZ system as well as binary oxides—PbO and ZrO2. Due to the comparatively complex phase character, the Curie temperature monitored by DTA, had a smeared appearance without pronounced maxima. The corresponding electrical properties are comparable with those typically observed for CaTiO3, but are worse than the normal values of bulk PZT due to defective stoichiometry.

Initiation of motion of a free‐standing body to base excitation

AbstractThis study is concerned with the conditions for the initiation of various modes of response of a free‐standing rigid body, initially at rest, placed on a frictional horizontal base which undergoes earthquake‐like accelerations in both the horizontal and vertical directions. These conditions are derived using equations of motion appropriate for each mode of motion. The analysis shows that an equivalent horizontal base acceleration may be constructed by dividing the time history of horizontal base acceleration by the sum of gravitational acceleration and the time history of vertical base acceleration. The criteria governing each mode of response of a body of given aspect ratio are then presented graphically with the magnitude of the equivalent base acceleration as abscissa and the coefficient of friction between the body and the base as ordinate. The study shows that a body is more stable while the vertical base acceleration is upwards than when it is absent as expected. When the vertical base acceleration is downwards, although the body is very likely to be lifted off the base, it is nevertheless possible to rock, and slide and rock simultaneously provided the value of coefficient of friction is sufficiently high and the downward vertical base acceleration is not too different from gravitational acceleration. Copyright © 2007 John Wiley & Sons, Ltd.

Estimating Sliding Displacement of an Unanchored Body Subjected to Earthquake Excitation

A freestanding rigid body under the action of base excitation can move in many different ways. In this study, the sliding response of a body is considered. The body is placed on a horizontal base that undergoes a one-dimensional horizontal motion. In 1965, Newmark (1965) gave a simple formula to determine the sliding distance of a freestanding body subjected to a single rectangular acceleration pulse of short duration at the base. The objective of this study is to see if this formula can be applied to estimate the sliding displacement of a body under the action of real earthquakes. Newmark's formula calls for the maximum velocity of the base which information is usually not directly available. To make use of the response spectrum commonly available to the engineers, Newmark's formula is first re-derived and expressed in terms of the maximum displacement of the base, which can be determined from the absolute displacement response spectrum in low frequency range. An ensemble of 75 real earthquakes is then employed, the equation of sliding motion is solved numerically and the average of the maximum sliding displacement of the body relative to the base is computed. The computed displacement is then compared with that obtained by Newmark's formula. This is done for a body placed on the ground as well as on the floors of a building. It is shown that Newmark's formula can be used if an adjustment factor, as suggested in this study, is applied. Key words: earthquake, sliding, unanchored body

Pore and Structure Formation in Collagen-Hydroxyapatite Precursors: Experiment-Model

In this paper we discuss different routes for the formation of collagen/HAP-composites with graded porosity. We show experimental evidence of the pore growth during phase separation of an aqueous collagen solution and investigate the influence of different mechanical boundary conditions (freestanding body, film on rigid substrate). The formation of a graded pore structure via phase separation is presented as well as the successful synthesis of a collagen/HAP.-composite via a cementation reaction from a colloidal HAP-precursor. In the modelling part we focus on the drying process as a route for graded densification and structure formation. We present a brief description of the model used to investigate stress formation and plastic deformation in a two-phase material containing a liquid and a solid phase. We outline the important processing and material parameters for structural design and show how the model can be used to find the optimum processing conditions for a desired graded structure.

Holocene Gypsum Types and Formative Processes in Tidal Flat Settings, Carnarvon Basin, Western Australia: ABSTRACT

Study of gypsum presently forming in terrigenous and carbonate tidal flats along the semiarid coastline of Western Australia indicates that gypsum crystal habits, textures, structures, and fabrics developed on or within host sediments can be correlated with the physical, chemical, and hydrologic conditions of formation. By treating the study of gypsum from a sedimentologic approach, a classification of gypsum types is developed which allows comparative analysis and appears to be applicable to the interpretation of ancient evaporitic sequences. Gypsum precipitated on a substrate from a free-standing body of water crystallizes in a habit dominated by the prism (110) and displays variations in texture, fabric, and structure that are related to the maintenance or progressive change in environmental conditions within the brine body. The action of physical and organic agencies is important in the genesis of the fabrics and structures displayed and in their destruction to form clastic gypseous sediments. Gypsum precipitated within a host sediment crystallizes in a habit dominated by the hemi pyramid (111) and displays textures, fabrics, and structures that are related to host sediment properties, brine chemistry, ground-water hydrology, and the mechanisms for maintenance of such environmental conditions. Gypsum emplacement acts to disrupt and modify sedimentary features within the host and to form new textures, fabrics, and structures which are related to, and overpoint, their precursors. End_of_Article - Last_Page 556------------