8,553 research outputs found
Physical metallurgy of nickel aluminides
A description of the important physical metallurgy aspects of Ni3Al and NiAl encompassing structure, crystallographic defects, slip systems and phase stability has been presented in this article. The microstructures generated in the two alloys by conventional as well as novel processing techniques have been discussed. The effect of alloying additions on the microstructure has been enumerated. Besides description of the aforementioned physical metallurgy aspects, an important purpose of this review is to focus on the reasons of brittleness in the two alloys and means of alleviating this problem primarily by alloying. The effect of alloying on the slip behaviour has also been described
Effects of different doses of x-rays on meiotic chromosomes of malePhysopelta schlanbuschi (Largidae: Heteroptera)
Male largid bugs,Physopelta schlanbuschi, having 2n=17 chromosomes (12 autosomes +2m+X1X2Y), were irradiated with x-ray doees of 300 r, 400 r and 500 r which yielded various types of chromosome aberrations in different stages of meiosis of which the common forms were breaks, fragment of unknown origin, constriction, gap etc. Among the 3 sex chromosomes, the two conspicuously large markers, X1 and Y, sometimes formed chiasmalike configuration in prophase I and metaphase I, while a number of anaphase I plates had a chromatid bridge, very likely formed by the X1 and the Y. The qualitative and quantitative assessments of chromosome aberrations in spermatogonial metaphase, prophase I, metaphase I, anaphase I and metaphase II were made at 13 intervals for the doses of 300 r and 400 r and 14 intervals for 500 r between 5 min and 1 week or more. The data showed over-all dose-dependent aberration effects and the sex chromosomes appeared relatively more vulnerable than the autosomes to different doses of x-rays. The testes of untreated males taken as controls had practically no aberration
Effects of partial crystallinity and quenched-in defects on corrosion of a rapidly solidified Ti-Cu alloy
Rapid solidification by planar flow casting has been found to have introduced deficiencies, viz. partial crystallinity, air pockets and compositional difference in the ribbons of rapidly solidified Ti42.9Cu57.1 alloy. In order to investigate the effects of these deficiencies on the corrosion of rapidly solidified Ti42.9Cu57.1 alloy ribbons, electrochemical behaviour of alloy ribbons has been investigated in the acidic chloride environments at room temperature by taking into consideration each side of the alloy ribbon separately. The alloy displayed passivity followed by pitting corrosion. In the as- solidified condition, air pockets appear to be the most detrimental defect from the viewpoint of corrosion resistance of the alloy ribbons
Precipitation hardening in 350 grade maraging steel
Evolution of microstructure in a 350 grade commercial maraging steel has been examined. In the earlier stages of aging, the strengthening phases are formed by the heterogeneous precipitation, and these phases have been identified as intermetallic compounds of the Ni3 (Ti, Mo) and Fe2Mo types. The kinetics of precipitation are studied in terms of the activation energy by carrying out isothermal hardness measurements of aged material. The mechanical properties in the peak-aged and overaged conditions were evaluated and the flow behavior examined. The overaging behavior of the steel has been studied and the formation of austenite of different morphologies identified. The crystallography of the austenite has been examined in detail. From the microstructural examination of peak-aged and deformed samples, it could be inferred that the dislocation-precipitate interaction is by precipitate shearing. Increased work hardening of the material in the overaged condition was suggestive of looping of precipitates by dislocations
A note on matrix model with IR cutoff and AdS/CFT
We propose an effective model of strongly coupled gauge theory at finite
temperature on in the presence of an infrared cutoff. It is constructed
by considering the theory on with an infrared cutoff and then taking the
size of the to infinity while keeping the cutoff fixed. This model
reproduces various qualitative features expected from its gravity dual.Comment: 27 pages, 9 figures, an appendix added, other minor changes, journal
versio
Compacton like breathers in nonlinear anharmonic Lattice with nonlocal dispersive interaction
Approximation of corner polyhedra with families of intersection cuts
We study the problem of approximating the corner polyhedron using
intersection cuts derived from families of lattice-free sets in .
In particular, we look at the problem of characterizing families that
approximate the corner polyhedron up to a constant factor, which depends only
on and not the data or dimension of the corner polyhedron. The literature
already contains several results in this direction. In this paper, we use the
maximum number of facets of lattice-free sets in a family as a measure of its
complexity and precisely characterize the level of complexity of a family
required for constant factor approximations. As one of the main results, we
show that, for each natural number , a corner polyhedron with basic
integer variables and an arbitrary number of continuous non-basic variables is
approximated up to a constant factor by intersection cuts from lattice-free
sets with at most facets if and that no such approximation is
possible if . When the approximation factor is allowed to
depend on the denominator of the fractional vertex of the linear relaxation of
the corner polyhedron, we show that the threshold is versus .
The tools introduced for proving such results are of independent interest for
studying intersection cuts
- …