459 research outputs found
An alternate model for magnetization plateaus in the molecular magnet V_15
Starting from an antiferromagnetic Heisenberg Hamiltonian for the fifteen
spin-1/2 ions in V_15, we construct an effective spin Hamiltonian involving
eight low-lying states (spin-1/2 and spin-3/2) coupled to a phonon bath. We
numerically solve the time-dependent Schrodinger equation of this system, and
obtain the magnetization as a function of temperature in a time-dependent
magnetic field. The magnetization exhibits unusual patterns of hysteresis and
plateaus as the field sweep rate and temperature are varied. The observed
plateaus are not due to quantum tunneling but are a result of thermal
averaging. Our results are in good agreement with recent experimental
observations.Comment: Revtex, 4 pages, 5 eps figure
Interacting Generalised Cosmic Chaplygin gas in Loop quantum cosmology: A singularity free universe
In this work we investigate the background dynamics when dark energy is
coupled to dark matter with a suitable interaction in the universe described by
Loop quantum cosmology. Dark energy in the form of Generalised Cosmic Chaplygin
gas is considered. A suitable interaction between dark energy and dark matter
is taken into account in order to at least alleviate (if not solve) the cosmic
coincidence problem. The dynamical system of equations is solved numerically
and a stable scaling solution is obtained. A significant attempt towards the
solution of the cosmic coincidence problem is taken. The statefinder parameters
are also calculated to classify the dark energy model. Graphs and phase
diagrams are drawn to study the variations of these parameters. It is seen that
the background dynamics of Generalised Cosmic Chaplygin gas is completely
consistent with the notion of an accelerated expansion in the late universe.
From the graphs, generalised cosmic Chaplygin gas is identified as a dark fluid
with a lesser negative pressure compared to Modified Chaplygin gas, thus
supporting a 'No Big Rip' cosmology. It has also been shown that in this model
the universe follows the power law form of expansion around the critical point,
which is consistent with the known results. Future singularities that may be
formed in this model as an ultimate fate of the universe has been studied in
detail. It was found that the model is completely free from any types of future
singularities.Comment: 10 pages, 10 figures. arXiv admin note: text overlap with
arXiv:1109.1481, arXiv:1102.275
Magnetization of Mn_12 Ac in a slowly varying magnetic field: an ab initio study
Beginning with a Heisenberg spin Hamiltonian for the manganese ions in the
Mn_12 Ac molecule, we find a number of low-energy states of the system. We use
these states to solve the time-dependent Schrodinger equation and find the
magnetization of the molecule in the presence of a slowly varying magnetic
field. We study the effects of the field sweep rate, fourth order anisotropic
spin interactions and a transverse field on the weights of the different states
as well as the magnetization steps which are known to occur in the hysteresis
plots in this system. We find that the fourth order term and a slow field sweep
rate are crucial for obtaining prominent steps in magnetization in the
hysteresis plots.Comment: LaTeX, 11 pages, 12 eps figure
Magnetic Anisotropy in the Molecular Complex V15
We apply degenerate perturbation theory to investigate the effects of
magnetic anisotropy in the magnetic molecule V15. Magnetic anisotropy is
introduced via Dzyaloshinskii-Moriya (DM) interaction in the full Hilbert space
of the system. Our model provides an explanation for the rounding of
transitions in the magnetization as a function of applied field at low
temperature, from which an estimate for the DM interaction is found. We find
that the calculated energy differences of the lowest energy states are
consistent with the available data. Our model also offers a novel explanation
for the hysteretic nature of the time-dependent magnetization data.Comment: Final versio
Dynamics of Interacting Generalized Cosmic Chaplygin gas in Brane-world scenario
In this work we explore the background dynamics when dark energy is coupled
to dark matter with a suitable interaction in the universe described by brane
cosmology. Here DGP and the RSII brane models have been considered separately.
Dark energy in the form of Generalized Cosmic Chaplygin gas is considered. A
suitable interaction between dark energy and dark matter is considered in order
to at least alleviate (if not solve) the cosmic coincidence problem. The
dynamical system of equations is solved numerically and a stable scaling
solution is obtained. A significant attempt towards the solution of the cosmic
coincidence problem is taken. The statefinder parameters are also calculated to
classify the dark energy models. Graphs and phase diagrams are drawn to study
the variations of these parameters. It is also seen that the background
dynamics of Generalized Cosmic Chaplygin gas is consistent with the late cosmic
acceleration, but not without satisfying certain conditions. It has been shown
that the universe in both the models follows the power law form of expansion
around the critical point, which is consistent with the known results. Future
singularities were studied and our models were declared totally free from any
types of such singularities. Finally, some cosmographic parameters were also
briefly studied. Our investigation led to the fact that although GCCG with a
far lesser negative pressure compared to other DE models, can overcome the
relatively weaker gravity of RS II brane, with the help of the negative brane
tension, yet for the DGP brane model with much higher gravitation, the
incompetency of GCCG is exposed, and it cannot produce the accelerating
scenario until it reaches the phantom era.Comment: 34 pages, 30 figures. arXiv admin note: substantial text overlap with
arXiv:1204.3531, arXiv:1109.1481, arXiv:1109.357
FGF8 isoform b expression in human prostate cancer.
Overexpression of fibroblast growth factor 8 (FGF8) mRNA has been previously described in prostate cancer. Of its four isoforms, FGF8b is thought to be the most important in carcinogenesis. We hypothesised that immunodetection of FGF8b in archival prostate cancer specimens is of potential prognostic value. Using a selected cohort of prostate tumours from transurethral (n=30) and radical prostatectomies (n=59), an optimised protocol for FGF8b immunoreactivity was used to corroborate expression with clinical parameters. No expression was observed in benign prostates (n=10). In prostate cancer, immunoreactivity was localised to the malignant epithelium with weak signals in the adjacent stroma. Expression of FGF8b in stage T1 and T2 cancers were 40 and 67%, respectively. In contrast, FGF8b expression was present in 94% of T3 and 100% of T4 cancers. By histological grade, FGF8b was found in 41% of low-grade cancers (Gleason score 4-6), 60% of intermediate-grade cancers (Gleason score 7 and 92% of high-grade cancers (Gleason score 8-10). The intensity of expression was significantly associated with stage (P=0.0004) and grade (P<0.0001) of disease. We further hypothesised that FGF8b overexpression resulted from enhanced transcription and translation rather than from abnormalities involving the FGF8 gene locus. This was tested by means of fluorescent in situ hybridisation in 20 cancer specimens to map the FGF8 gene locus. FGF8 gene copy number in benign and malignant nuclei was found to be similar (2.33+/-0.57 and 2.0+/-0.81, respectively P=0.51). Based on these findings, we propose a multicentre study on cohorts of patients to further evaluate FGF8b as a potential prognostic marker in prostate cancer
Relational approaches to poverty in rural India: social, ecological and technical dynamics
Poverty is now widely recognised as multidimensional, with indicators including healthcare, housing and sanitation. Yet, relational approaches that foreground political-cultural processes remain marginalised in policy discourses. Focusing on India, we review a wide range of relational approaches to rural poverty. Beginning with early approaches that focus on structural reproduction of class, caste and to a lesser extent gender inequality, we examine new relational approaches developed in the last two decades. The new approaches examine diverse ways in which poverty is experienced and shapes mobilisations against deprivation. They draw attention to poor peopleâs own articulations of deprivation and alternate conceptions of well-being. They also show how intersecting inequalities of class, caste and gender shape governance practices and political movements. Despite these important contributions, the new relational approaches pay limited attention to technologies and ecologies in shaping the experience of poverty. Reviewing studies on the Green Revolution and wider agrarian transformations in India, we then sketch the outlines of a hybrid relational approach to poverty that combines socio-technical and -ecological dynamics. We argue that such an approach is crucial to challenge narrow economising discourses on poverty and to bridge the policy silos of poverty alleviation and (environmentally) sustainable development
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