56 research outputs found
Condensation and Evaporation of Mutually Repelling Particles :Steady states and limit cycles
We study condensation and evaporation of particles which repel each other,
using a simple set of rules on a square lattice. Different results are obtained
for a mobile and an immobile surface layer.A two point limit cycle is observed
for high temperature and low pressure in both cases. Here the coverage
oscillates between a high and a low value without ever reaching a steady state.
The results for the immobile case depend in addition on the initial coverage.Comment: 8 pages, 3 figure
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
Preclinical Testing of Metabolic Inhibitors with Erlotinib in Renal Medullary Carcinoma
https://openworks.mdanderson.org/sumexp23/1099/thumbnail.jp
Hypoxia inducible factor 1a in kidney cancer
https://openworks.mdanderson.org/sumexp23/1120/thumbnail.jp
Effect of size reduction on the ferromagnetism of the manganite La1-xCaxMnO3 (x = 0.33)
In this paper we report an investigation on the ferromagnetic state and the
nature of ferromagnetic transition of nanoparticles of
using magnetic measurements and neutron
diffraction. The investigation was made on nanoparticles with crystal size down
to nm. The neutron data show that even down to a size of nm the
nanoparticles show finite spontaneous magnetization () although the value
is much reduced compared to the bulk sample. We observed a non-monotonic
variation of the ferromagnetic to paramagnetic transition temperature
with size and found that initially enhances on size reduction, but
for nm it decreases again. The initial enhancement in was
related to an increase in the bandwidth that occured due to a compaction of the
Mn-O bond length and a straightening of the Mn-O-Mn bond angle, as determined
form the neutron data. The size reduction also changes the nature of the
ferromagnetic to paramagnetic transition from first order to second order with
critical exponents approaching mean field values. This was explained as arising
from a truncation of the coherence length by the finite sample size.Comment: 12 figure
Geometric and disorder -- type magnetic frustration in ferrimagnetic "114" Ferrites: Role of diamagnetic Li+ and Zn2+ cation substitution
The comparative study of the substitution of zinc and lithium for iron in the
"114" ferrites, YBaFe4O7 and CaBaFe4O7, shows that these diamagnetic cations
play a major role in tuning the competition between ferrimagnetism and magnetic
frustration in these oxides. The substitution of Li or Zn for Fe in the cubic
phase YBaFe4O7 leads to a structural transition to a hexagonal phase
YBaFe4-xMxO7, for M = Li (0.30 < x < 0.75) and for M = Zn (0.40 < x < 1.50). It
is seen that for low doping values i.e. x = 0.30 (for Li) and x = 0.40 (for
Zn), these diamagnetic cations induce a strong ferrimagnetic component in the
samples, in contrast to the spin glass behaviour of the cubic phase. In all the
hexagonal phases, YBaFe4-xMxO7 and CaBaFe4-xMxO7 with M = Li and Zn, it is seen
that in the low doping regime (x ~ 0.3 to 0.5), the competition between
ferrimagnetism and 2 D magnetic frustration is dominated by the average valency
of iron. In contrast, in the high doping regime (x ~ 1.5), the emergence of a
spin glass is controlled by the high degree of cationic disorder, irrespective
of the iron valency.Comment: 2 tables, 7 figure
"The fruits of independence": Satyajit Ray, Indian nationhood and the spectre of empire
Challenging the longstanding consensus that Satyajit Ray's work is largely free of ideological concerns and notable only for its humanistic richness, this article shows with reference to representations of British colonialism and Indian nationhood that Ray's films and stories are marked deeply and consistently by a distinctively Bengali variety of liberalism. Drawn from an ongoing biographical project, it commences with an overview of the nationalist milieu in which Ray grew up and emphasizes the preoccupation with colonialism and nationalism that marked his earliest unfilmed scripts. It then shows with case studies of Kanchanjangha (1962), Charulata (1964), First Class Kamra (First-Class Compartment, 1981), Pratidwandi (The Adversary, 1970), Shatranj ke Khilari (The Chess Players, 1977), Agantuk (The Stranger, 1991) and Robertsoner Ruby (Robertson's Ruby, 1992) how Ray's mature work continued to combine a strongly anti-colonial viewpoint with a shifting perspective on Indian nationhood and an unequivocal commitment to cultural cosmopolitanism. Analysing how Ray articulated his ideological positions through the quintessentially liberal device of complexly staged debates that were apparently free, but in fact closed by the scenarist/director on ideologically specific notes, this article concludes that Ray's reputation as an all-forgiving, ‘everybody-has-his-reasons’ humanist is based on simplistic or even tendentious readings of his work
Transport properties of nanoparticles of complex oxides: likely presence of coulomb blockade at low temperature
In this paper we report transport properties at low temperatures (3 K≤T≤300 K) in nanostructured functional oxides. Electrical resistivity in the nanoparticles of La<SUB>0.5</SUB>Sr<SUB>0.5</SUB>CoO<SUB>3</SUB> (LSCO), a ferromagnet, show a gradual change-over from a completely metallic state (in the bulk sample) to a completely insulating state (in the sample with the smallest particle size of ∼35 nm), while still remaining a ferromagnet, albeit with a lower T<SUB>C</SUB>. In the LSCO nanoparticles (diameter <60 nm) there is a change-over in the temperature dependence of the resistivity at the lowest temperature (T<10 K) which we could identify as arising from the Coulomb blockade in the conducting grains which are separated by insulating grain boundaries that allow transport by tunneling. However, nanoparticles of the nonmagnetic material, LaNiO<SUB>3</SUB> (LNO) remain metallic (similar to the bulk sample) throughout the temperature range studied with the resistivity reaching a temperature independent value at the lowest temperature measured. We suggest that the essential difference between the electrical transport in these nanostructured materials arises due to the physical nature of the grain boundaries which is insulating in LSCO due to absence of long range spin order that is needed for the metallic state
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