A HREM study of the interfaces between TiO2 precipitates and the Al2O3 matrix in star sapphire

1992 ◽  
Vol 50 (1) ◽  
pp. 228-229
Author(s):  
S.Q. Xiao ◽  
A. H. Heuer ◽  
P. Pirouz
Keyword(s):  
Cross Section ◽  
Lattice Mismatch ◽  
Misfit Dislocations ◽  
Regular Array ◽  
Lattice Constants ◽  
Small Precipitate ◽  
S Matrix ◽  
The Matrix ◽  
The Mean ◽  
The Cross

The asterism, or star effect, present in star sapphire (Ti-doped A12O3) single crystals is known to arise from the needle-like rutile(r) (TiO2) precipitates in the sapphire(s) matrix. The specific orientation relationship between the precipitates and the matrix is {100}r//{0003}s and <011>r//<1010>s . In this work we report a HREM study of the rutile/sapphire interface.The cross-section perpendicular to the needle axis of a very small precipitate, which is coherent, or has just one misfit dislocation at its interface, is a rhombus; the precipitate/matrix interface (habit plane) is {111}r{1123}s. As the coherency break down and misfit dislocations are introduced into the interface, the shape of the cross-section becomes nearly square; the two orthogonal interfaces are {100}r//0003}s and {011}r//{1120}s. Larger precipitates show rectangular interfaces elongated along the {100}r//{0003}s interface (Fig.l). A regular array of misfit dislocations with Burger vector b = 1/3<0001>S are present at the {011}r//{1120}s interface, the mean distance between every two adjacent 1/3<0001>S misfit dislocations being 8.7 nm which compensates exactly the 5.9% lattice mismatch estimated from the lattice constants of these two structures. Similarly, a regular array of misfit dislocations with Burgers vector b = 1/3<1010>S at the {100}r//{0003}s interface compensates the 4.5% lattice mismatch at that interface.

The determination of the cross sections for the reactions 27 Al( n , α ) and 56 Fe( n , p ) for 14 MeV neutrons by an absolute method

1966 ◽  
Vol 292 (1429) ◽  
pp. 180-192 ◽  
Keyword(s):  
Cross Section ◽  
Cross Sections ◽  
Standard Error ◽  
Particle Method ◽  
Systematic Errors ◽  
Aluminium Foil ◽  
The Mean ◽  
The Cross ◽  
Experimental Values

Measurements of the cross sections for the reactions 27 Al( n , α ) 24 Na and 56 Fe( n, p ) 56 Mn for neutrons of energy 13.5 ± 0.1 MeV have been made by a radioactivation method. The neutron flux was determined by a variant of the 'associated particle’ method, in which the α -particles produced concurrently with the neutrons from the D + T reaction were estimated in terms of the volume of helium which accumulated when they were brought to rest in an aluminium foil. Cross section values obtained at 13.5 MeV were: for 27 Al( n , α ): 118.1 ± 6.0 mb : for 56 Fe( n, p ): 106.7 ± 4.7 mb. The errors quoted include both the standard error on the mean of the experimental values and an estimate of possible residual systematic errors. The excitation functions for both reactions in the energy region 13.5 to 14.8 MeV have also been investigated, in order to provide secondary cross section values over this range of energies. At 14.8 MeV the values found were: 27 Al( n , α )103.6 ± 5.5 mb; 56 Fe( n, p )96.7 ± 4.5 mb.

scholarly journals STUDIES ON CILIA

1965 ◽  
Vol 26 (3) ◽  
pp. 805-834 ◽  
Author(s):  
Peter Satir
Keyword(s):  
Cross Section ◽  
Length Change ◽  
The Body ◽  
Cell Of Origin ◽  
Ciliary Movement ◽  
The Matrix ◽  
Morphological Specialization ◽  
Dense Band ◽  
The Cross ◽  
Different Order

Termination of peripheral filaments of the axoneme of gill cilia of fresh-water mussels (Elliptio or Anodonta) occurs in characteristic fashion: (a) subfiber b of certain doublets ends leaving a single simplified tubular unit; (b) the wall of the unit becomes thick and may even obliterate the interior; and (c) the filament drops out of the 9 + 2 pattern. The order in which doublets begin simplifying is also characteristic. This may be determined by numbering the filaments, those with the bridge being 5–6, with the direction of numbering determined by the apparent enantiomorphic configuration (I to IV) of the cross-section. Shorter filaments can be identified in simplifying tips with mixed double and single peripheral units. In this material, laterofrontal cirri show a morphological specialization in the region where individual cilia simplify. The cilia studied run frontally from the body of the cirrus and point in the direction of effective stroke. The longest filaments (Nos. 3, 4, 5, 6, 7) appear as the doublets at the bottom of the cross-section, nearest the surface of the cell of origin. Above them, and above the central pair, a dark band (a section of a dense rod) runs through the matrix. The remaining filaments are the single units. Effective-pointing frontal and lateral ciliary tips end in a fashion similar to laterofrontal tips, although no dense band is present. For all effective-pointing tips studied, the order in which the peripheral filaments end appears to be Nos. (9, 1), 8, 2, 7, 6, 3, 4, 5. However, recovery-pointing lateral tips show a different order: Nos. 7, 6, 8, 5, 9, 4, 1 (3, 2), although the longer filaments are still at the bottom of the cross-section. In simple models of ciliary movement involving contraction of the peripheral filaments, filaments at the top of the cross-section should be longer, if any are. Such models are not supported by the evidence here. These results can be interpreted as supporting sliding-filament models of movement where no length change of peripheral filaments occurs.

Physical analysis of the fleece of sheep for biological purposes. II. Estimation of the number and mean diameter of wool fibres from a cast of their cross-section

1951 ◽  
Vol 2 (2) ◽  
pp. 195 ◽  
Author(s):  
LT Wilson
Keyword(s):  
Cross Section ◽  
Unit Area ◽  
Physical Analysis ◽  
Mean Diameter ◽  
The Mean ◽  
The Cross ◽  
Limits Of Error

A technique has been developed for making a cast of the cross-section of a bundle of wool fibres under defined packing conditions. By counting the fibre impressions per unit area in representative portions of the cast, both the total number of fibres and the mean diameter can be rapidly calculated within fairly close limits of error.

The initial dispersion of contaminant in Poiseuille flow and the smoothing of the snout

1976 ◽  
Vol 77 (3) ◽  
pp. 593-602 ◽  
Author(s):  
P. C. Chatwin
Keyword(s):  
Cross Section ◽  
Poiseuille Flow ◽  
Molecular Diffusion ◽  
Lateral Diffusion ◽  
Longitudinal Diffusion ◽  
Molecular Diffusivity ◽  
Discharge Velocity ◽  
Smoothing Process ◽  
The Mean ◽  
The Cross

In Poiseuille flow in a circular tube passive contaminant initially spread uniformly over the cross-section would be pulled out in a paraboloidal snout in the absence of any diffusive mechanism, and there would be a discontinuity in $\overline{C}$, the mean concentration over the cross-section, associated with the contaminant at the front of the snout. In reality molecular diffusion smooths out this snout in two ways: direct longitudinal diffusion and the interaction between lateral diffusion and advection. The effect of these two mechanisms is discussed, and determined for small values of κt/a2, where t is the time since injection, κ is the molecular diffusivity and a is the tube radius. For such values, important in many applications, the tube walls play no part in the smoothing process. It is shown that for $\kappa t/a^2 < 0.25(\overline{u}a/\kappa)^{-\frac{2}{3}}$, where $\overline{u}$ is the discharge velocity, the effect of longitudinal diffusion dominates over that of the interaction, which is, in turn, dominant for $\kappa t/a^2 > 2.5(\overline{u}a/\kappa)^{-\frac{2}{3}}$, when $\overline{C}$ is close to the form described by Lighthill (1966).

Construction of Strained SrTiO3/BaTiO3 Superlattices and Their Dielectric Properties

1994 ◽  
Vol 361 ◽  
Author(s):  
Hitoshi Tabata ◽  
Hidekazu Tanaka ◽  
Tomoji Kawai
Keyword(s):  
Dielectric Constant ◽  
Lattice Mismatch ◽  
High Energy ◽  
Dielectric Constants ◽  
In Situ Monitoring ◽  
Misfit Dislocations ◽  
Lattice Constants ◽  
Applied Frequency ◽  
Artificial Dielectric ◽  
Unit Cells

ABSTRACTArtificial dielectric superlattices of SrTiO3/BaTiO3(STO/BTO) and CaTiO3/BaTiO3 (CTO/BTO) have been formed by a pulsed laser ablation technique with an in situ monitoring of RHEED (reflection high energy electron diffraction) oscillation. The crystal structures can be controlled with atomic order accuracy and a large stress of 400–500 MPa is introduced at the interface between the BTO and STO layers. Xhe superlattices show higher dielectric constant than that of (Sr0.5Ba0.5)TiO3 films against the change of temperature or applied frequency. A large dielectric constant of 900 was observed for the superlattices with a stacking periodicity of 2 unit cells / 2 unit cells. Xhe superlattices show drastically different electrical behavior from that of the solid solution (Sr,Ba)XiO3 films, both with changing temperature and applied frequency. Broad maxima of the dielectric constants occur around 40–50 °C and the values remain large even for the temperature above 200 °C. On the contrary, in the case of CTO/BTO superlattices, lattice constants and dielectric constant do not change so much compared with STO/BTO cases. Lattice mismatch in the STO/BTO and the CTO/BTO superlattices are 2.5% and 5.5%, respectively. In the case of CTO/BTO, misfit dislocations such as stacking faults may occur at the interface between CTO and BTO layers owing to large lattice mismatch. Therefore, lattice strain is introduced effectively below the lattice mismatch of about 3%.

Planar Defects, Voids and their Relationship in 3C-SiC Layers

2005 ◽  
Vol 483-485 ◽  
pp. 189-192
Author(s):  
David Méndez ◽  
A. Aouni ◽  
Daniel Araújo ◽  
Gabriel Ferro ◽  
Yves Monteil ◽  
...  
Keyword(s):  
Cross Section ◽  
Lattice Mismatch ◽  
Misfit Dislocations ◽  
Lateral Growth ◽  
Si Substrate ◽  
Transmission Electron Microscopy Micrographs ◽  
Planar Defects ◽  
Transmission Electron ◽  
The Relationship

One of the problems with Si(001)/3C-SiC templates is that they involve highly defective interfaces due to the presence of misfit dislocations, voids and planar defects that degrade the SiC layer quality. A way to accommodate the high lattice mismatch between these materials and reduce the voids density is to carbonize the Si substrate before the epitaxial growth. In this contribution an alternative way to reduce planar defects density is presented by analyzing the relationship between planar defects and voids. Planar view and cross section transmission electron microscopy micrographs show a diminution of planar defects in the regions surrounding the voids. Due to the lower elastic energy over the voids and/or to a lateral growth in these regions, the generation of planar defects is partially deactivated, improving locally the crystalline quality of the SiC layer. The introduction of such cavities can be thus seen as a new parameter of Si/SiC templates design.

16O–16O ELASTIC SCATTERING AT 350 MeV AND POLE STRUCTURE OF THE S-MATRIX

1998 ◽  
Vol 13 (03) ◽  
pp. 211-217 ◽  
Author(s):  
V. V. PILIPENKO
Keyword(s):  
Elastic Scattering ◽  
Cross Section ◽  
Matrix Model ◽  
Regge Pole ◽  
S Matrix ◽  
Pole Structure ◽  
The Cross

The cross-section of the 16 O –16 O elastic scattering at 350 MeV including rainbow-like structures has been described on the basis of an original S-matrix model taking account of the effect of a Regge pole in the first quadrant of the complex l-plane.

On the dispersion of a solute in a fluid flowing through a tube

1956 ◽  
Vol 235 (1200) ◽  
pp. 67-77 ◽  
Keyword(s):  
Diffusion Coefficient ◽  
Cross Section ◽  
Molecular Diffusion ◽  
Simultaneous Action ◽  
Mean Velocity ◽  
Molecular Diffusion Coefficient ◽  
Rate Of Growth ◽  
The Mean ◽  
The Cross ◽  
Dimension Characteristic

Sir Geoffrey Taylor has recently discussed the dispersion of a solute under the simultaneous action of molecular diffusion and variation of the velocity of the solvent. A new basis for his analysis is presented here which removes the restrictions imposed on some of the para­meters at the expense of describing the distribution of solute in terms of its moments in the direction of flow. It is shown that the rate of growth of the variance is proportional to the sum of the molecular diffusion coefficient, D , and the Taylor diffusion coefficient Ka 2 U 2 / D , where U is the mean velocity and a is a dimension characteristic of the cross-section of the tube. An expression for k is given in the most general case, and it is shown that a finite distribution of solute tends to become normally distributed.

scholarly journals The angular distribution of protons projected by fast neutrons

1937 ◽  
Vol 163 (913) ◽  
pp. 265-281 ◽  
Keyword(s):  
Angular Distribution ◽  
Binding Energy ◽  
Cross Section ◽  
Direct Evidence ◽  
Fast Neutrons ◽  
Proton Scattering ◽  
Potential Well ◽  
The Mean ◽  
The Cross ◽  
Square Hole

The nature of the interaction between neutron and proton has assumed great importance in modern nuclear theory, since it is now generally assumed that these two particles form the fundamental constituents of all nuclei. Little direct evidence exists, however, as to the nature of this interaction. The stable existence of the deuteron shows that the force between neutron and proton is attractive, and for purposes of calculation a “square hole” potential well has generally been assumed. With this model some success has been obtained* in correlating the magnitudes of a number of experimentally measurable quantities such as ( a ) the binding energy of the deuteron, ( b ) the total cross-section for neutron-proton scattering (Tuve and Hafstad 1936; Amaldi and Fermi 1936 a ), ( c ) the cross-section for photo­ electric disintegration of the deuteron (Chadwick and Goldhaber 1935), and ( d ) the cross-section for capture of neutrons by protons (Amaldi and Fermi 1936 b ). The interaction is not completely derivable from the above data, since the values of these quantities depend mainly upon r 2 V , where r is the mean radius and V is the depth of the potential hole.

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