22,761 research outputs found
Heat Treatment of Forgings
Ferrous materials are widely used for the manufacture of components for the engineering applications. This is because of the fact that these materials can have wide range of mechanical properties. According to requirements one can select a particular grade of iron and steel and by
suitable processes shapes can be given and then by heat treatment the required physical properties can be impa-rted. Application and use of steel is much more wide than that of iron is well known, because of its improved
characteristic as regards hot and cold deformation
Electrical transport properties of nanostructured ferromagnetic perovskite oxides La_0.67Ca_0.33MnO_3 and La_0.5Sr_0.5CoO_3 at low temperatures (5 K > T >0.3 K) and high magnetic field
We report a comprehensive study of the electrical and magneto-transport
properties of nanocrystals of La_0.67Ca_0.33MnO_3 (LCMO) (with size down to 15
nm) and La_0.5Sr_0.5CoO_3 (LSCO) (with size down to 35 nm) in the temperature
range 0.3 K to 5 K and magnetic fields upto 14 T. The transport,
magnetotransport and non-linear conduction (I-V curves) were analysed using the
concept of Spin Polarized Tunnelling in the presence of Coulomb blockade. The
activation energy of transport, \Delta, was used to estimate the tunnelling
distances and the inverse decay length of the tunnelling wave function (\chi)
and the height of the tunnelling barrier (\Phi_B). The magnetotransport data
were used to find out the magnetic field dependences of these tunnelling
parameters. The data taken over a large magnetic field range allowed us to
separate out the MR contributions at low temperatures arising from tunnelling
into two distinct contributions. In LCMO, at low magnetic field, the transport
and the MR are dominated by the spin polarization, while at higher magnetic
field the MR arises from the lowering of the tunnel barrier by the magnetic
field leading to an MR that does not saturate even at 14 T. In contrast, in
LSCO, which does not have substantial spin polarization, the first contribution
at low field is absent, while the second contribution related to the barrier
height persists. The idea of inter-grain tunnelling has been validated by
direct measurements of the non-linear I-V data in this temperature range and
the I-V data was found to be strongly dependent on magnetic field. We made the
important observation that a gap like feature (with magnitude ~ E_C, the
Coulomb charging energy) shows up in the conductance g(V) at low bias for the
systems with smallest nanocrystal size at lowest temperatures (T < 0.7 K). The
gap closes as the magnetic field and the temperature are increased.Comment: 13 figure
Structure of A=138 isobars above the 132Sn core and the N-N interaction in the neutron-rich environment
Large basis untruncated shell model calculations have been done for the A=138
neutron -rich nuclei in the pi(gdsh) X nu(hfpi) valence space above the 132Sn
core. Two (1+2) -body nuclear Hamiltonians, viz., realistic CWG and empirical
SMPN in this model space have been used. Calculated ground state binding
energies, level spectra and other spectroscopic properties have been compared
with the available experimental data. Importance of untruncated shell model
calculations in this model space has been pointed out. Shell model results for
the very neutron rich Sn isotope (138Sn, N/Z=1.76) of astrophysical interest
for which no spectroscopic information except beta -decay half life is
available, have been presented. Shell structure and evolution of collectivity
in the even-even A=138 isobars have been studied as a function of valence
neutron and /or proton numbers. Calculations done for the first time, reproduce
remarkably well the collective vibrational states in 138Te and 138Xe.
Comparison of some of the important two-body matrix elements of the empirical
SMPN, CW5082 and the realistic CWG interactions has been done. These matrix
elements are important for ground state binding energies and low-lying spectra
of nuclei in this region. Consideration of the predictability of the two
interactions seems to suggest that, in order to incorporate the special
features of the N-N interaction in such exotic n-rich environment above the
132Sn core, the use of local spectroscopic information from the region might be
essential.Comment: 22 pages, 14 figure
Investigation into the limits of perturbation theory at low Q^2 using HERA deep inelastic scattering data
A phenomenological study of the final combined HERA data on inclusive deep
inelastic scattering (DIS) has been performed. The data are presented and
investigated for a kinematic range extending from values of the four-momentum
transfer, , above 10 GeV down to the lowest values observable at
HERA of = 0.045 GeV and Bjorken , = 6
10. The data are well described by fits based on perturbative quantum
chromodynamics (QCD) using collinear factorisation and evolution of the parton
densities encompassed in the DGLAP formalism from the highest down to
of a few GeV. The Regge formalism can describe the data up to 0.65 GeV. The complete data set can be described by a new fit
using the ALLM parameterisation. The region between the Regge and the
perturbative QCD regimes is of particular interest.Comment: 38 pages, 13 figure
Testing gravity at the Second post-Newtonian level through gravitational deflection of massive particles
Expression for second post-Newtonian level gravitational deflection angle of
massive particles is obtained in a model independent framework. Several of its
important implications including the possibility of testing gravitational
theories at that level are discussed.Comment: 5 pages, couple of equations of the previous version are correcte
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