Boundary Tracing Research Articles

Electron Microscope Studies of the Deviation of a Stress-Annealed Pyrolytic Graphite Matrix from a Single Crystal

By means of a preferential etch technique in conjunction with transmission electron microscopy, a stress-annealed pyrolytic graphite has been shown to be a compact of crystallites with La values typically lying in the range 1–40 μ. The boundaries defining these crystallites varied from the low-angle tilt boundaries θ∼1′, found in Ticonderoga crystals, to high-angle boundaries denoting misorientations of up to 30°. In contrast to the low over-all boron concentration of the material, 1–2 ppm wt/wt, the concentration of this element residing in the intercrystallite boundaries was calculated at ∼103 ppm wt/wt. This provides confirmation of the premise that the lattice disorder existing across a boundary trace supports a vacancy concentration far in excess of that pertaining to more perfect regions of the graphite. It is postulated that at temperatures >2100°C this enhanced vacancy concentration will allow a dynamic interchange mechanism for crystallite growth, having an activation energy given by E* = ½(Efv + Efi) + Emai. Nonbasal screws have a deleterious effect on the rate of graphitization for two principal reasons. First, the nonbasal screws residing in intercrystallite boundaries effectively stabilize the excessive vacancy concentration at the latter sites. Second, if the distance of closest approach of these dislocations becomes less than some critical value, they may be responsible for creating new boundaries. As it appears unlikely that many formal boundaries, which can be described in terms of lattice defects, will exist between neighboring crystallites in pyrolytic graphite, the initial stages of graphitization must occur by an alternative mechanism. The recent work of Murty would seem to imply that the latter is in fact an interstitial mechanism, having an activation energy of 9.8±0.7 eV as compared to the value of 8.3±0.3 eV predicted for the dynamic interchange mechanism.

Origin of preferred orientation in columnar ice

A general rule has been developed to account for the preferred orientation of naturally-occuring and laboratory-grown columnar ice. A reference plane is established which is normal to the segment of a grain boundary trace at the ice-water interface. For a particular grain and grain boundary, the critical region of the reference plane is the quadrant bounded by z and y, y being directed towards the grain boundary. The preferred orientation can best be predicted by summing the crystallographic components c z ' and a z ' of these crystal axes whose projection onto the reference plane lies in the critical quadrant. Grain B will be wedged out by grain A where the sum of the crystallographic components in the z direction is greater for grain B than for grain A. The analysis indicates that the preferred orientation depends on the equilibrium profile of the grain boundary at the ice-water interface.

純アルミニウム双結晶の高温引張りクリープによる結晶粒界すべりの研究

During the creep test in vacuum at high temperatures under constant tensile load, with their boundaries aligned at 45 deg. to the tensile axis of 99.99% aluminium bicrystal specimens, grain boundary sliding and shear deformation near the boundary were measured. The grain boundary sliding was accompanied by crystal shear deformation near the boundary, and the observed grain boundary displacement had no relation with the boundary misorientation angle ω, but with the angle α or β between the crystal slip plane trace and the boundary trace at the observed plane of the bicrystal specimen.The sliding along the boundary with a large misorientation angle ω acted preferencially on the boundary itself (pure sliding), and the sliding along the small misorientation angle boundary was shear deformation of component crystals adjacent to the boundary (zone sliding). The over-all deformation (elongation) of the specimen was measured without observable crystal slip within component crystals. And migration of the common boundary proceeded in the direction to release the strain energy of plastic deformation that occurred locally from the boundary irregulalities to the component crystals. At 350°C or 400°C, sub-boundaries owing to the rearrangement of dislocations and subgrains were observed near the common boundary.The initial grain boundary displacement was proportional to creep time, and the obtained activation energy for the boundary sliding of the specimen with a boundary misorientation angle ω of 43 deg. was 27600 cal/mol, which coincided well with the value of activation energy for plastic deformation by crystal slip in the aluminium single crystal.

Grain Boundary Sliding in Bicrystals of Tin

AbstractBicrystals of tin were tested in shear over a range of stresses and temperatures near the melting‐point. Boundary sliding occurred initially at a constant rate, followed by a period of steadily decreasing rate until movement almost ceased; the initial rate data fell into two clearly defined groups. In a few specimens, sudden increases in sliding rate were observed. Values were calculated for the activation energy and the stress dependence of the initial rate of sliding. During a test, the boundary trace on one of the bicrystal surfaces became very irregular. A straight trace could be regained by electropolishing the surface and an increased rate of sliding was obtained if the specimen was retested.

Mise en evidence des anciens joints de grains γ dans les alliages uranium-molybdene a faible teneur

Two methods used to obtain preferential evidence of the late grain boundaries in U-0.5-1.5% Mo alloys are presented. The first method involves very short electrolytic repolishing of the samples previously polished and attacked. The second polishing diminishes the anodic attack of the matrix (to lamellar structure) and causes the grain boundaries to stand out clearly. The second methods involves electrolytic attack after passivation of the polished surfaces. Thus the matrix (lamellar structure) is strongly colored while the borders corresponding to the traces of late grain boundaries appear in white. (P.C.H.)

Minumum-Mass Thin Fins which Transfer Heat Only by Radiation to Surroundings at Absolute Zero

Previous article Next article Minumum-Mass Thin Fins which Transfer Heat Only by Radiation to Surroundings at Absolute ZeroJ. Ernest Wilkins, Jr.J. Ernest Wilkins, Jr.https://doi.org/10.1137/0108047PDFBibTexSections ToolsAdd to favoritesExport CitationTrack CitationsEmail SectionsAbout[1] E. Schmidt, Die Warmeübertragung durch Rippen, Z. Verein. Deutsch. Ing., 70 (1926), 885–889 Google Scholar[2] R. J. Duffin, A variational problem relating to cooling fins, J. Math. Mech., 8 (1959), 47–56 MR0103711 0087.09901 ISIGoogle Scholar[3] J. G. Bartas and , W. H. Sellers, Radiation fin effectiveness, Trans. A.S.M.E., Ser. C, Journal of Heat Transfer, 82 (1960), 73–75 CrossrefGoogle Scholar[4] J. P. Callinan and , W. P. Brggren, Some radiator design criteria for space vehicles, Trans. A.S.M.E., Ser. C, Journal of Heat Transfer, 81 (1959), 237–244 CrossrefGoogle Scholar Previous article Next article FiguresRelatedReferencesCited byDetails Near-Exact Radiating Fins via Boundary TracingConway Li, Neville Fowkes, Brendan Florio, and Miccal Matthews26 July 2022 | SIAM Journal on Applied Mathematics, Vol. 82, No. 4AbstractPDF (772 KB)Boundary Tracing for Laplace's Equation with Conformal MappingConway Li, Neville Fowkes, and Miccal Matthews2 August 2022 | SIAM Journal on Applied Mathematics, Vol. 82, No. 4AbstractPDF (593 KB)On the Nonlinear Method of Wilkins for Cooling Fin OptimizationS. Bhargava and R. J. Duffin17 February 2012 | SIAM Journal on Applied Mathematics, Vol. 24, No. 4AbstractPDF (554 KB)A Variational Problem with Applications to Cooling FinsChen-Ya Liu13 July 2006 | Journal of the Society for Industrial and Applied Mathematics, Vol. 10, No. 1AbstractPDF (727 KB)Minimum-Mass Thin Fins and Constant Temperature GradientsJ. Ernest Wilkins, Jr.13 July 2006 | Journal of the Society for Industrial and Applied Mathematics, Vol. 10, No. 1AbstractPDF (845 KB)Minimum Mass Thin Fins with Specified Minimum ThicknessJ. Ernest Wilkins, Jr.10 July 2006 | Journal of the Society for Industrial and Applied Mathematics, Vol. 9, No. 2AbstractPDF (879 KB) Volume 8, Issue 4| 1960Journal of the Society for Industrial and Applied Mathematics History Submitted:22 October 1959Published online:10 July 2006 InformationCopyright © 1960 Society for Industrial and Applied MathematicsPDF Download Article & Publication DataArticle DOI:10.1137/0108047Article page range:pp. 630-639ISSN (print):0368-4245ISSN (online):2168-3484Publisher:Society for Industrial and Applied Mathematics

A Few Comments on Deformation of Jori (Rural Boundary) in Japan

Rural boundaries are the traces of the ancient adjustment of ricefields and are shown by narrow water channels and ridges between them which run crosswise and divide them into square lots called “tsubo” (about 100m by 100m). They were built up between 7th and 8th centuries and still remain as they were. The writer has investigated them in Saitama Prefecture in Kanto District, and has found several cases of their deformation, as they have been left alone without any readjustment since their construction, the district have been a kind of frontier of Japan. The following are some of these cases.Some square lots are deformed into paralleograms because they have been fields flooded for the cultivation of rice in the fans and waters of springs and streamlet have washed their edges, extending squares little by little down the slope in a very long period of time. (fig. 4, fig. 5, fig. 6)Some are changed into fields unfit for the cultivation of rice, as the river that flows near them has often overflowed and piled up much earth and sand on its banks and this has deprived the fields of irrigation facilities. (fig. 3, fig. 10.) In some places this is done on a much larger scale owing to the change of the course of rivers and some of these fields are subdivided into many smaller and irregular plots, while others show no trace of rural boundaries as is the case with those fields that are originally unsuitable for the cultivation of rice.The deformation of Jori must, therefore, be considered in relation to the passage of time. And this research throws light not only on the perpetuity of rural boundaries but on their changeableness as well.

The Royal Geographical Society's Work on the One-Million Map

MR. A. R. HINKS, secretary of the Royal Geographical Society, described at a recent meeting of the society the work which has been carried out, and is still in progress, on a map on the scale 1/1,000,000. It is well known that, before the outbreak of war, conferences of representatives of the principal Powers had met ill London and Paris, and had come to an agreement as to the production of a map on this scale, t6 cover ultimately all lands, on a uniform projection and with uniform methods of representation, etc. A few sheets had been produced in various countries. They were scattered, in some instances imperfect and not available in any quantity, and in any event useless to meet even partially the necessity which was felt, almost at the outset of the war, of a map to cover uniformly Western and Central Europe and Asia Minor and adjacent areas affected by military operations. Even for Europe no such map existed, and it was necessary, in taking a broad view of the operations, or for any such purpose as that which will ultimately become of prime importance, the tracing of boundaries, to pass at certain points from maps of a particular scale and method to others totally different in every respect. People are prone to comment that the scale 1/1,000,000 (nearly, 16 miles = 1 inch) is too small even for such general purposes, but it is not so. It allows the representation of important places, railways, roads and boundaries, rivers, and elevation by means of contour lines, either alcne or in conjunction with layer colours.