1,740 research outputs found
Utilisation of Iron ore Fines in Alternative Iron making processes - An Indian perspective
Extraction of metallic iron from iron bearing ores is the basis of iron and steel industry. Extensive mechanized mining and advanced beneficiation techniques to meet the oxide feed requirements of Blast Furnace, Direct Reduction and Smelting Reduction processes are resulting in gene-ration of macro and micro fines/slimes (washed fines)
in various mine sites of the country. Though a part of the fines, mainly macro ones, in the agglomerated form, that is either as sinter or pellet have found use in various iron making processes, the problem still persist with utilization of micro fines. It is understood that Bailadila
mines of NMDC alone account for an estimated amount of 11 Mt of slimes. Besides, substantial amount of fines is also accumulated in different mine sites. Partial utilization of mined output is not only affecting internal resource conservation but also contributing to pollution and envir-onmental problems.
In this paper, an attempt has been made to focus on various processes/technologies available today, utilizing the iron oxide fines and applicability of the same under Indian conditions. Further, based on available information indicative techno-economics have been spelt out
Spin-gap effect on resistivity in the t-J model
We calculate the spin-gap effect on dc resistivity in the t-J model of
high- cuprates by using the Ginzburg-Landau theory coupled with a
gauge field as its effective field theory to get , where is the spin-gap onset temperature. By taking the
compactness of massive gauge field into account, the exponent deviates from
its mean-field value 1/2 and becomes a nonuniversal -dependent quantity,
which improves the correspondence with the experiments.Comment: 4 pages, REVTeX format, 2 eps-figure
The Two-Dimensional S=1 Quantum Heisenberg Antiferromagnet at Finite Temperatures
The temperature dependence of the correlation length, susceptibilities and
the magnetic structure factor of the two-dimensional spin-1 square lattice
quantum Heisenberg antiferromagnet are computed by the quantum Monte Carlo loop
algorithm (QMC). In the experimentally relevant temperature regime the
theoretically predicted asymptotic low temperature behavior is found to be not
valid. The QMC results however, agree reasonably well with the experimental
measurements of La2NiO4 even without considering anisotropies in the exchange
interactions.Comment: 4 Pages, 1 table, 4 figure
Entanglement Entropy of Random Fractional Quantum Hall Systems
The entanglement entropy of the and quantum Hall
states in the presence of short range random disorder has been calculated by
direct diagonalization. A microscopic model of electron-electron interaction is
used, electrons are confined to a single Landau level and interact with long
range Coulomb interaction. For very weak disorder, the values of the
topological entanglement entropy are roughly consistent with expected
theoretical results. By considering a broader range of disorder strengths, the
fluctuation in the entanglement entropy was studied in an effort to detect
quantum phase transitions. In particular, there is a clear signature of a
transition as a function of the disorder strength for the state.
Prospects for using the density matrix renormalization group to compute the
entanglement entropy for larger system sizes are discussed.Comment: 29 pages, 16 figures; fixed figures and figure captions; revised
fluctuation calculation
Theory of d-density wave viewed from a vertex model and its implications
The thermal disordering of the -density wave, proposed to be the origin of
the pseudogap state of high temperature superconductors, is suggested to be the
same as that of the statistical mechanical model known as the 6-vertex model.
The low temperature phase consists of a staggered order parameter of
circulating currents, while the disordered high temperature phase is a
power-law phase with no order. A special feature of this transition is the
complete lack of an observable specific heat anomaly at the transition. There
is also a transition at a even higher temperature at which the magnitude of the
order parameter collapses. These results are due to classical thermal
fluctuations and are entirely unrelated to a quantum critical point in the
ground state. The quantum mechanical ground state can be explored by
incorporating processes that causes transitions between the vertices, allowing
us to discuss quantum phase transition in the ground state as well as the
effect of quantum criticality at a finite temperature as distinct from the
power-law fluctuations in the classical regime. A generalization of the model
on a triangular lattice that leads to a 20-vertex model may shed light on the
Wigner glass picture of the metal-insulator transition in two-dimensional
electron gas. The power-law ordered high temperature phase may be generic to a
class of constrained systems and its relation to recent advances in the quantum
dimer models is noted.Comment: RevTex4, 10 pages, 11 figure
Effect of RF power on the structural, optical and gas sensing properties of RF-sputtered Al doped ZnO thin films
The effect of Radio Frequency (RF) power on the properties of magnetron sputtered Al doped ZnO thin films and the related sensor properties are investigated. A series of 2 wt% Al doped ZnO; Zn0.98Al0.02O (AZO) thin films prepd. with magnetron sputtering at different RF powers, are examd. The structural results reveal a good adhesive nature of thin films with quartz substrates as well as increasing thickness of the films with increasing RF power. Besides, the increasing RF power is found to improve the crystallinity and grain growth as confirmed by X-ray diffraction. On the other hand, the optical transmittance is significantly influenced by the RF power, where the transparency values achieved are higher than 82% for all the AZO thin films and the estd. optical band gap energy is found to decrease with RF power due to an increase in the crystallite size as well as the film thickness. In addn., the defect induced luminescence at low temp. (77 K) and room temp. (300 K) was studied through photoluminescence spectroscopy, it is found that the defect d. of electronic states of the Al3+ ion increases with an increase of RF power due to the increase in the thickness of the film and the crystallite size. The gas sensing behavior of AZO films was studied for NO2 at 350 °C. The AZO film shows a good response towards NO2 gas and also a good relationship between the response and the NO2 concn., which is modeled using an empirical formula. The sensing mechanism of NO2 is discussed
Critical exponents of the quantum phase transition in a planar antiferromagnet
We have performed a large scale quantum Monte Carlo study of the quantum
phase transition in a planar spin-1/2 Heisenberg antiferromagnet with CaV4O9
structure. We obtain a dynamical exponent z=1.018+/-0.02. The critical
exponents beta, nu and eta agree within our errors with the classical 3D O(3)
exponents, expected from a mapping to the nonlinear sigma model. This confirms
the conjecture of Chubukov, Sachdev and Ye [Phys. Rev. B 49, 11919 (1994)] that
the Berry phase terms in the planar Heisenberg antiferromagnet are dangerously
irrelevant.Comment: 5 pages including 4 figures; revised version: some minor changes and
added reference
The NMR relaxation rate of O in undoped Sr_2CuO_2Cl_2: Probing two-dimensional magnons at short distances
We calculate the nuclear relaxation rate of oxygen in the undoped quasi
two-dimensional quantum Heisenberg antiferromagnet Sr_2CuO_2Cl_2 above the Neel
temperature. The calculation is performed at two-loop order with the help of
the Dyson-Maleev formulation of the spin-wave expansion, taking all scattering
processes involving two and three magnons into account. At low temperatures T
we find 1 / T_1 = c_1 T^3 + c_2 T^4 + O (T^5), and give explicit expressions
for the coefficients c_1 (two-magnon scattering) and c_2 (three magnon
scattering). We compare our result with a recent experiment by Thurber et al.
and show that this experiment directly probes the existence of short-wavelength
magnons in a two-dimensional antiferromagnet.Comment: Final version, to appear in Phys. Rev. B (1 August 1997
Theory of the c-Axis Penetration Depth in the Cuprates
Recent measurements of the London penetration depth tensor in the cuprates
find a weak temperature dependence along the c-direction which is seemingly
inconsistent with evidence for d-wave pairing deduced from in-plane
measurements. We demonstrate in this paper that these disparate results are not
in contradiction, but can be explained within a theory based on incoherent
quasiparticle hopping between the CuO2 layers. By relating the calculated
temperature dependence of the penetration depth \lambda_c(T) to the c-axis
resistivity, we show how the measured ratio \lambda_c^2(0) / \lambda_c^2(T) can
provide insight into the behavior of c-axis transport below Tc and the related
issue of ``confinement.''Comment: 4 pages, REVTEX with psfig, 3 PostScript figures included in
compressed for
Superconductor-Insulator Transition in a Capacitively Coupled Dissipative Environment
We present results on disordered amorphous films which are expected to
undergo a field-tuned Superconductor-Insulator Transition.The addition of a
parallel ground plane in proximity to the film changes the character of the
transition.Although the screening effects expected from "dirty-boson" theories
are not evident,there is evidence that the ground plane couples a certain type
of dissipation into the system,causing a dissipation-induced phase
transition.The dissipation due to the phase transition couples similarly into
quantum phase transition systems such as superconductor-insulator transitions
and Josephson junction arrays.Comment: 4 pages, 4 figure
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