Showing papers by "Wright-Patterson Air Force Base published in 1968"

Gadolinium Molybdate, a New Type of Ferroelectric Crystal

Abstract: Ferroelectric properties in gadolinium molybdate are shown to originate from a new mechanism completely different from that in conventional ferroelectric materials. In this crystal the spontaneous polarization results from an elastic instability which gives rise to a spontaneous strain in the original piezoelectric paraelectric phase. The dielectric permittivity of the clamped crystal ($\ensuremath{\epsilon}_{33}^{x}$) is low and independent of temperature, while the elastic constant ($c_{66}^{E}$) shows a strong temperature dependence with a marked anomaly at the Curie point.

Ribbon Reinforcement of Composites

Abstract: : A clear demonstration of the potential of ribbon-shaped reinforcements in composite materials applications is presented. From a micromechanics analysis, supported by experimental results. Ribbon reinforcement offers superior stiffness properties in the plane of the lamina. The macromechanics analysis introduces the concept of a hybrid composite in which the engineer may combine the outstanding strength properties of fibers with the superior stiffness properties offered by ribbon reinforcements. It is pointed out that the low strength observed for glass-ribbon composites is a consequence of fabrication procedures and does not correspond to the theoretical limiting strength of ribbon reinforcements. The use of ribbon-shaped reinforcements also leads to composites which will have very small isotropic thermal expansion coefficients in the plane of the plate. Thus, ribbon reinforcements provide an attractive means of achieving intermediate to high performance composite possessing dimensional stability. (Author)

Tension Buckling of Anisotropic Cylinders

Abstract: The nature of the extensional response of anisotropic cylinders, such as helical-wound composite tubes, tinder various end conditions is investigated analytically and experimentally. Of particular interest is the existence of a uniform state of stress under practical testing conditions. Also considered is the influence of end constraint on the stability of thin tubes.

The conference on standardization of anthropometric techniques and terminology (a report)

Abstract: The conference, attended by anthropologists, engineers, dental and medical researchers, physical educationists and statisticians, took place on 28–30 March 1967 in the Aerospace Medical Research Laboratories, Wright-Patterson Air Force Base, Ohio. The ultimate purpose was to improve the comparability of anthropometric data from all workers, by establishing standards for the many new dimensions required in engineering anthropology, and by developing a terminology that reconciles the new standards with previous usages. In this effort, the group selected a list of dimensions (though with dissent on type and number) recommended as a minimum for all human biological surveys; and they chose from previous usage a terminological structure whose form, content and mode of presentation they recommended as standard practice by all anthropometrists. Both official and dissenting lists are presented, and the terminological structure is described, with examples. Despite solid progress toward a standardized technology encompassing both classical and modern practices, the conference left numerous points of technique or terminology unsettled, some of which are briefly described. Hence future meetings appear necessary, perhaps annually, until such remaining problems can be resolved.

Thermally stable polymers from 1,4,5,8‐naphthalenetetracarboxylic acid and aromatic tetraamines

Abstract: Polycondensations of 1,4,5,8-naphthalenetetracarboxylic acid (NTCA) with both 3,3′-diaminobenzidine (DAB) and 1,2,4,5-tetraaminobenzene tetrahydrochloride (TAB) in polyphosphoric acid (PPA) were found to produce soluble polymers which exhibit excellent thermal stabilities. Polymer structures were deduced from infrared, thermal, and elemental analyses of model compounds and polymers. Polymer derived from TAB had a ladder-type structure. Polymers with solution viscosities near 1 or above (determined in H2SO4) were obtained from polymerizations near 200°C., and analysis showed these to possess a very high degree of completely cyclized benzimidazobenzophenanthroline structure. Less vigorous reaction conditions gave polymers with lower solution viscosities which appeared to be less highly cyclized. Low-viscosity polymer was also prepared from DAB and NTCA by solid-phase polycondensation. Some advancements in the solution viscosities of polymers synthesized from DAB in PPA were caused by second staging in the solid phase.

Response of the body to mechanical forces‐an overview*

Abstract: Environmental mechanical forces can act on man in many different First, there is the variation in force application: forces can be airor liquidtransmitted, as are blast waves, where more or less uniform pressure acts over large parts of the body or major segments of it. Or the forces can be applied locally to the body surfaces, as in most impact and blow conditions or when a projectile hits the surface. Finally, there are the inertial forces resulting from motions of the body as a whole acting on all tissue and also on all deep-seated organs of the body. In blast exposure, potentially all three types of force application are involved. Crash or impact injury involves forces of both the second and third type, while the acceleration forces encountered in aerospace flight are predominantly of the third type. The second classification of forces would be according to their time function: the force functions can be nonperiodic blast waves, or structure-transmitted impacts lasting from a few milliseconds to several seconds or longer; or, the forces can be more or less periodic or random continuous such as the pressure waves of sound or the vibration and buffeting in tractors, tanks, or aerospace vehicles. The third classification is according to the physical amplitude of the force and, as a consequence, according to the biological response of interest. For example, blast biology is primarily concerned with the effects of shock waves of large amplitude, with the resulting physical injury, and with survival capability. A physically very similar shock wave of orders of magnitude smaller amplitude is responsible for the sonic boom generated by supersonic aircraft. In the latter instance, the biological questions of interest are quite different, embracing the auditory phenomenon of loudness and the possible annoyance by too frequent occurrence.3 With respect to the effects of the forces of sound waves and structure-borne vibrations ranging from the weakest environmental stimuli to the most intense, one is interested in all possible biological responses, from the threshold of perception through the wide range of possible interference with task performance or normal living (effect of noise on speech communication, effects of noise or vibrations on psychomotor performance, annoyance, etc. ) , up to the range of reversible or irreversible injury to the organism.4*5 It is obvious that in spite of the enormous differences among the environments of interest-in the mode of force transmission, in the time function, and in the specific biological reaction of concern-there are many findings, facts, and principles that apply to several or all of these problem areas. It is primarily the physical reaction of the human body to the force environment, the tissue deformation resulting from the mechanical stresses, that makes this statement true. For in practically all cases it is not the pressure per se but the resulting relative displace-

Spatial resolution of the volume emission coefficient in strongly self-absorbing sources of cylindrical symmetry.

Abstract: It is shown that the equations relating the radial profiles of the volume emission and absorption coefficients to the transmission and emitted intensity profiles in self-absorbing cylindrically symmetric sources, can be written in such a way that the problem of spatially resolving the volume emission coefficient gives rise to a Volterra integral equation of the second kind in a standard form. The theory of equations of this type is invoked to show the formal convergence of an iterative solution to the problem, subject only to a finite transmission and bounded slope to the absorption coefficient. A prescription for applying this iterative procedure is given that involves a series of numerical integrations and Abel inversions, and the convergence of some numerical solutions is demonstrated.

Internal-Conversion-Electron Study of the Decay of Ru 103

Abstract: The $\ensuremath{\beta}$ decay of ${\mathrm{Ru}}^{103}$ (39.6 d) has been investigated with an iron-core, $\ensuremath{\pi}\sqrt{2}$ double-focussing $\ensuremath{\beta}$-ray spectrometer. The internal-conversion-electron spectrum revealed the presence of $\ensuremath{\gamma}$ rays of 609.89(24), 556.85(22), 496.88(16), 443.85(15), 294.88(16), 53.11(3), and 39.55(4) keV. No new lines with an intensity greater than 1.6% of the $497K$ line were found. The $67K$ line was found to have an intensity less than 0.17%, and the $322K$ and $362K$ lines an intensity less than 0.3%, of the $497K$ line. Limitations on the multipolarities and mixing ratios of some of the transitions have been determined through $\frac{K}{L}$- and $L$-subshell ratios, and through internal-conversion-coefficient measurements. The multipolarities obtained for the seven observed transitions were compared with $\ensuremath{\gamma}\ensuremath{-}\ensuremath{\gamma}$ angular-correlation results. This resulted in the spin-parity assignments of ${\frac{7}{2}}^{+}$, ${\frac{7}{2}}^{+}$, and ${\frac{7}{2}}^{\ensuremath{-}}$ for the 39.55(4)-, 92.66(5)-, and 649.48(24)-keV states, respectively. The 536.47(16)-keV level is shown to have a spin parity of either ${\frac{3}{2}}^{+}$ or ${\frac{7}{2}}^{\ensuremath{-}}$.

Harmonic and Null Descriptions of Gravitational Radiation

Abstract: : The problem of an axially symmetric space-time containing gravitational waves in the usual Bondi null coordinate system is considered. This Bondi frame is then related to asymptotically harmonic coordinates by means of a characteristic initial value problem. The resultant functional relationship between the null and asymptotically harmonic frames is used to transform Bondi's radiative metric into its equivalent asymptotically harmonic form. This is then compared to the radiative solution which Fock has calculated directly using harmonic coordinates. In agreement with Fock, one finds that the harmonic form of the radiation metric contains logarithmic terms. The treatment clearly shows that these logarithmic metric components do not result from the well known logarithmic terms in the harmonic coordinate description of the light cones for Schwarzschild-like geometries. The principal result of this paper is that they arise from higher order radiative corrections.

Polycarboxyhydrazides with ferrocenylene groups in the main chain

Abstract: Polycarboxyhydrazides essentially of the type are synthesized by low-temperature solution condensation of 1,1′-di(chlorocarbonyl) ferrocene with hydrazine or 1, 1′-ferrocenedicarboxyhydrazide and hexamethylphosphoramide as solvent. In an analogous manner the polycondensation of 1, 1′-di(chlorocarbonyl)ferrocene with oxalyldihydrazide leads to polyhydrazides essentially possessing the structure . Both polymer types exhibit inherent viscosities (0.08–0.19 dl./g.) considerably lower than reported for analogous aliphatic or benzene-aromatic polyhydrazides. This behavior points to premature chain termination via heterobridging imide groups as a result of the welldocumented tendency of appropriately substituted ferrocene compounds to undergo intramolecular cyclization. In addition, elemental analytical and spectroscopic evidence, coupled with the failure of both polymer types to undergo cyclodehydration to the corresponding 1,3,4-oxadiazole polymers upon heat treatment, suggests some structural irregularities in the aliphatic connecting segments arising from ferrocenoylation of secondary amino groups with resultant branching. With the polyhydrazide prepared from 1, 1′-di(chlorocarbonyl)ferrocene and 1, 1′-ferrocenedicarboxyhydrazide it is shown spectroscopically that treatment with alkali results in conversation of the nonconjugated hydrazide structure of the connecting segments into the polyconjugated tautomeric enol form comprising azine groups.

Phase relations and substructure in single-crystal MoSi2

Abstract: Single-crystal specimens of MoSi 2 were found to have a second phase present, identified as Mo 5 Si 3 by X-ray diffraction and electron microprobe analyses. Isothermal annealing runs on bulk samples in vacuum at temperatures ranging from 1200 ° to 1600 °C for 24 h showed an increase in Mo 5 Si 3 content with increasing annealing temperature. High-temperature X-ray diffraction on thin layers in vacuum showed an increase of Mo 5 Si 3 content with a concomitant decrease of MoSi 2 up to 1550 °C, using Mo heaters. From 1550 ° to 1720 °C, a decrease in Mo 5 Si 3 content was noted. Mass spectrometry up to 1700 °C in a vacuum of 10 −6 mm Hg did not reveal Mo-Si molecular species. Samples etched with 4 H 2 O : 1 HF : 2 HNO 3 showed the presence of individual and polygonized, chain-like, elliptical etch pits on the (001) plane. Rectangular, triangular, spiral, and hexahedral etch pits were found primarily on the (100) plane, the lattice indicating the pseudo-hexagonal character of MoSi 2 by analogy with WSi 2 . Primary slip produced by hardness indentations at room temperature was found to be of the {100} type, and secondary slip of the {110} type was also determined for MoSi 2 . The Knoop microhardness values at 100 g loads ranged from 870 to 1300 kg/mm 2 for MoSi 2 . Mo 5 Si 3 was found to have a microhardness value ranging from 1190 to 1330 kg/mm 2 .

Investigation of flow separation over a rearward-facing step in a hypersonic stream.

Abstract: Abstract : An experimental investigation was conducted for hypersonic flow over a rearward-facing step. The inviscid dominated region around this configuration was investigated by the method of rotational characteristics. The recirculation region was described by a primary expansion angle for the dividing streamline. The calculated results were compared with the experimental measurements as the critical verification. This comparison exhibited a favorable substantiation for the present analysis. Static pressure distributions on the model surface and impact pressure surveys were presented along with visual observations. A study of the three-dimensional effects on the finite span 'two-dimensional' model is also presented. (Author)

Hypersonic lifting body optimization.

Abstract: Lifting hypersonic configurations were optimized to produce maximum lift-drag ratios. Simplified aerodynamic equations (with Newtonian pressure and laminar skin friction proportional to the inverse root of length) were written for a generalized shape with ten degrees of geometric freedom; a numerical searching routine was employed to ascertain the optimum vehicle. Constraints of volumetric efficiency, nose-heating limit, and skin friction were imposed singly and in combination. In general, the derived configurations tended towards delta planforms when the leading-edge bluntness drag exceeded the skin-friction drag, and for the alternate situation, the planforms were trapezoidal. Geometric details of the optimal configurations are tabulated for each set of constraints. Experimental correlation of the mathematical model for the aerodynamic characteristics was obtained by conducting a wind-tunnel test at a Mach number of 14 to obtain the lift-drag ratio. The results provided confidence in the adequacy of the formulation.

Approximate Solution of the Laminar Boundary-Layer Equations with Mass Transfer

Abstract: The Galerkin-Kantorovich-Dorodnitsyn (GKD) multimoment method is employed for the calculation of compressible steady laminar boundary-layer flows around two-dimensional and axially symmetric bodies with insulated walls and mass transfer. The two basic elements of the GKD method are a system of N integral conditions derived from the boundary-layer equations and an approximating function with N undetermined coefficients. Two forms of the approximating function are employed: one throughout most regions of flow and the other in the immediate vicinity of zero wall shear stress. Approximate solutions for a variety of similar and nonsimilar flows are presented. The trial calculations include cases with flow separation, blowoff, and discontinuities in the boundary conditions. The approximate solutions are generally uniformly convergent as the number of coefficients is increased and are less than about 1 % in error for the third- and higher-order solutions except in the neighborhood of blowoff on a flat plate.