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Preparation and Structural Investigation of Bi16(Sr,Ca)14O38 (1997)

Wong-Ng, Winnie ; Roth, Robert S. ; Rawn, Claudia J.

Westerville, Ohio : American Ceramics Society

Journal of the American Ceramic Society 80 (1997), S. 0

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ISSN: 1551-2916

Source: Blackwell Publishing Journal Backfiles 1879-2005

Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics

Notes: Single-crystal X-ray diffraction was used to investigate the structure of the ternary oxide of approximate formula Bi14(Sr,Ca)12O33. The crystal examined was found to have a composition Bi2Sr0.68Ca1.07O4.75 or Bi16Sr5.44Ca8.56O38 as a result of refinement. It crystallizes in the monoclinic space group (C2/m), with cell parameters a= 21.764 (4) A, b= 4.3850 (13)° A, c= 12.905 (3) A, β= 102.72 (2)°, and V 1201.2 (5) A3. Strontium and calcium ions were found to substitute for each other. The structure consists of a network of alkaline-earth oxide polyhedra with broad channels parallel to the b axis, in which the bismuth ions reside. Two out of four crystallographically distinct Bi ions form infinite Bi—O zigzag ribbons of edge-linked Bi—O units, while each of the other two form oxygen corner-shared Bi—O chains along b. The lone pair electrons of the Bi ions point toward each other in the channels.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1111/j.1151-2916.1997.tb02833.x

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Estimating the dynamic coefficient of friction from experimental data: the motion of a rocket inside a smoothbore launcher (1969)

Roth, Robert S.

Springer

Experimental mechanics 9 (1969), S. 565-570

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ISSN: 1741-2765

Source: Springer Online Journal Archives 1860-2000

Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics

Notes: Abstract The motion of a spinning rocket inside a smoothbore launcher has drawn some attention in recent years. The inaccuracy of spin-stabilized rockets can be attributed, in part, to the initial motion of the rocket inside the smoothbore launcher. Recently, tests have indicated that a closer examination of the problem is required. The tests were performed to determine the time history of the spin and forward motion of the rocket by Fastax cameras. The evaluation of the data with respect to engineering-design parameters is difficult since the experimental results must be compared with an analytical model of the system. In this paper, the results of one test are reported and a nonlinear analytical model is used which includes both the rotary and forward motion of the rocket. The two motions are coupled through a dynamic friction coefficient. The intent of this paper is to show how an analytical model can be made to fit the experimental data, that is, the initial conditions and the coefficient of friction are found which define the solution giving the best least-square fit to the data.