7,345 research outputs found
Cytokeratin positivity in myxopapillary ependymoma – a potential diagnostic pitfall
<p>Abstract</p> <p>Background</p> <p>Myxopapillary ependymomas (MPE) occur in the filum terminale of the spinal cord, but also present in extra-spinal locations such as subcutaneous tissue and brain. They are slow growing grade I gliomas. Areas of solid growth pattern with aggregates of cells with "epithelioid morphology" seen in MPE can mimic metastatic carcinoma. The presence of occasional cells with clear cytoplasm and morphology can resemble Chordoma. Diagnosis can be missed due to these morphological similarities, which could affect patient management and hence, long term survival.</p> <p>Case presentation</p> <p>We describe two cases of MPE with cytokeratin (AE1 AE3, CAM 5.2, Cytokeratin 7 and cytokeratin 20) expression.</p> <p>Conclusion</p> <p>MPE can be positive for Cytokeratins (CAM 5.2, AE1 AE3, CK7) and focally for EMA, which could be misdiagnosed as metastatic carcinoma. In cases demonstrating epithelioid and clear cell morphology, the diagnosis of MPE should be made in conjunction with histology, proper immunohistochemical profile which includes co-expression of GFAP, S-100 protein and epithelial markers, radiologic findings and site. It is important to be aware of the cytokeratin profile in MPE to avoid erroneous diagnosis with other tumour entities.</p
The universe dynamics in the tachyon cosmology with non-minimal coupling to matter
Recently, the tachyon cosmology has been represented as dark energy model to
support the current acceleration of the universe without phantom crossing. In
this paper, we study the dynamics of the tachyon cosmology in which the field
plays the role of tachyon field and also non--minimally coupled to the matter
lagrangian. The model shows current universe acceleration and also phantom
crossing in the future. Two cosmological tests are also performed to validate
the model; the difference in the distance modulus and the model independent
Cosmological Redshift Drift (CRD) test.Comment: 14 pages, 11 figure
Kinematic alpha effect in isotropic turbulence simulations
Using numerical simulations at moderate magnetic Reynolds numbers up to 220
it is shown that in the kinematic regime, isotropic helical turbulence leads to
an alpha effect and a turbulent diffusivity whose values are independent of the
magnetic Reynolds number, \Rm, provided \Rm exceeds unity. These turbulent
coefficients are also consistent with expectations from the first order
smoothing approximation. For small values of \Rm, alpha and turbulent
diffusivity are proportional to \Rm. Over finite time intervals meaningful
values of alpha and turbulent diffusivity can be obtained even when there is
small-scale dynamo action that produces strong magnetic fluctuations. This
suggests that small-scale dynamo-generated fields do not make a correlated
contribution to the mean electromotive force.Comment: Accepted for publication in MNRAS Letter
Where are the degrees of freedom responsible for black hole entropy?
Considering the entanglement between quantum field degrees of freedom inside
and outside the horizon as a plausible source of black hole entropy, we address
the question: {\it where are the degrees of freedom that give rise to this
entropy located?} When the field is in ground state, the black hole area law is
obeyed and the degrees of freedom near the horizon contribute most to the
entropy. However, for excited state, or a superposition of ground state and
excited state, power-law corrections to the area law are obtained, and more
significant contributions from the degrees of freedom far from the horizon are
shown.Comment: 6 pages, 4 figures, Invited talk at Theory Canada III, Edmonton,
Alberta, Canada, June 16, 200
What can we say about seed fields for galactic dynamos?
We demonstrate that a quasi-uniform cosmological seed field is a much less
suitable seed for a galactic dynamo than has often been believed. The age of
the Universe is insufficient for a conventional galactic dynamo to generate a
contemporary galactic magnetic field starting from such a seed, accepting
conventional estimates for physical quantities. We discuss modifications to the
scenario for the evolution of galactic magnetic fields implied by this result.
We also consider briefly the implications of a dynamo number that is
significantly larger than that given by conventional estimates
Turbulent dynamo with advective magnetic helicity flux
Many astrophysical bodies harbor magnetic fields that are thought to be
sustained by a dynamo process. However, it has been argued that the production
of large-scale magnetic fields by mean-field dynamo action is strongly
suppressed at large magnetic Reynolds numbers owing to the conservation of
magnetic helicity. This phenomenon is known as {\it catastrophic quenching}.
Advection of magnetic fields by stellar and galactic winds toward the outer
boundaries and away from the dynamo is expected to alleviate such quenching.
Here we explore the relative roles played by advective and turbulent--diffusive
fluxes of magnetic helicity in the dynamo. In particular, we study how the
dynamo is affected by advection. We do this by performing direct numerical
simulations of a turbulent dynamo of type driven by forced
turbulence in a Cartesian domain in the presence of a flow away from the
equator where helicity changes sign. Our results indicate that in the presence
of advection, the dynamo, otherwise stationary, becomes oscillatory. We confirm
an earlier result for turbulent--diffusive magnetic helicity fluxes that for
small magnetic Reynolds numbers (\Rm\lesssim 100...200, based on the
wavenumber of the energy-carrying eddies) the magnetic helicity flux scales
less strongly with magnetic Reynolds number (\Rm^{-1/2}) than the term
describing magnetic helicity destruction by resistivity (\Rm^{-1}). Our new
results now suggest that for larger \Rm the former becomes approximately
independent of \Rm, while the latter falls off more slowly. We show for the
first time that both for weak and stronger winds, the magnetic helicity flux
term becomes comparable to the resistive term for \Rm\gtrsim 1000, which is
necessary for alleviating catastrophic quenching.Comment: 9 pages, 9 figures, accepted for publication in MNRA
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