5,244 research outputs found
Biaxial nematic phase in the Maier-Saupe model for a mixture of discs and cylinders
We analyze the global phase diagram of a Maier-Saupe lattice model with the
inclusion of disorder degrees of freedom to mimic a mixture of oblate and
prolate molecules (discs and cylinders). In the neighborhood of a Landau
multicritical point, solutions of the statistical problem can be written as a
Landau-de Gennes expansion for the free energy. If the disorder degrees of
freedom are quenched, we confirm the existence of a biaxial nematic strucure.
If orientational and disorder degrees of freedom are allowed to thermalize,
this biaxial solution becomes thermodynamically unstable. Also, we use a
two-temperature formalism to mimic the presence of two distinct relaxation
times, and show that a slight departure from complete thermalization is enough
to stabilize a biaxial nematic phase.Comment: 21 pages, 3 figure
Stable Umbral Chromospheric Structures
Aims. To understand the morphology of the chromosphere in sunspot umbra. We
investigate if the horizontal structures observed in the spectral core of the
Ca II H line are ephemeral visuals caused by the shock dynamics of more stable
structures, and examine their relationship with observables in the H-alpha
line. Methods. Filtergrams in the core of the Ca II H and H-alpha lines as
observed with the Swedish 1-m Solar Telescope are employed. We utilise a
technique that creates composite images and tracks the flash propagation
horizontally. Results. We find 0"15 wide horizontal structures, in all of the
three target sunspots, for every flash where the seeing was moderate to good.
Discrete dark structures are identified that are stable for at least two umbral
flashes, as well as systems of structures that live for up to 24 minutes. We
find cases of extremely extended structures with similar stability, with one
such structure showing an extent of 5". Some of these structures have a
correspondence in H-alpha but we were unable to find a one to one
correspondence for every occurrence. If the dark streaks are formed at the same
heights as umbral flashes then there are systems of structures with strong
departures from the vertical for all three analysed sunspots. Conclusions.
Long-lived Ca II H filamentary horizontal structures are a common and likely
ever-present feature in the umbra of sunspots. If the magnetic field in the
chromosphere of the umbra is indeed aligned with the structures, then the
present theoretical understanding of the typical umbra needs to be revisited.Comment: Accepted to Astronomy and Astrophysics. Online material (Fig3.mov and
Fig4.mov) will be available at A&
Measurement of miniband parameters of a doped superlattice by photoluminescence in high magnetic fields
We have studied a 50/50\AA superlattice of GaAs/AlGaAs
composition, modulation-doped with Si, to produce
cm electrons per superlattice period. The modulation-doping was tailored
to avoid the formation of Tamm states, and photoluminescence due to interband
transitions from extended superlattice states was detected. By studying the
effects of a quantizing magnetic field on the superlattice photoluminescence,
the miniband energy width, the reduced effective mass of the electron-hole
pair, and the band gap renormalization could be deduced.Comment: minor typing errors (minus sign in eq. (5)
Development of biocolonization resistant mortars: preliminary results
Restoration of Buildings and Monuments, vol. 13, nº 6 (2007), p.389-400The negative impact of biocolonization on buildings, particularly rendered ones, prompted the evaluation of a hydraulic mortar formulation to which copper metal, either as a powder or as fibres, was added as a means to control this problem. The study used in situ exposure in a location prone to biocolonization for over nine years.
The results have proved that over this time period, no biocolonization occurred on samples containing 0.35 % by weight of copper powder with regards to the dry mortar mix. The mortar proved to acquire a slightly
bluer-green hue which diminished after the nine year outdoor exposure. The mortars formulated with copper have a lower porosity as well as a lower capillary water absorption coefficient a definite advantage for their eventual life span. On the other hand, the mechanical resistance is slightly decreased but not significantly so.
Further studies are envisioned to assess the performance with other types of binder, such as aerial lime
Ex-utero intrapartum treatment (or EXIT procedure) in a case of cervical linfangiona
Introdução: Fetos com diagnóstico pré-natal de malformações anatómicas envolvendo a face e/ou o pescoço estão em risco de obstrução das vias aéreas desde o pós-natal imediato. A programação de medidas periparto que previnam a compressão das vias aéreas, mantendo uma adequada circulação fetal, é fundamental no prognóstico.
Caso ClÃnico: Feto com diagnóstico ecográfico, à s 31 semanas de gestação, de volumosa massa cervical e facial, compatÃvel com linfangioma quÃstico. O caso foi discutido em equipa multidisciplinar, tendo sido decidida a realização de cesariana associada ao procedimento EXIT à s 39 semanas de gestação. Após exteriorização do polo cefálico, foi confirmada massa cervical e facial direita, sendo o feto sujeito a intubação oro-traqueal no primeiro minuto. Ao sexto dia de vida foi submetido a cirurgia, com excisão parcial da massa.
Conclusão: O procedimento EXIT permite a manutenção de uma adequada oxigenação fetal enquanto se estabelece uma via aérea patente. Uma adequada coordenação da equipa multidisciplinar é fundamental para o êxito da técnic
Growth aspects of the marine microalga Nannochloropsis gaditana
Nannochloropsis is well appreciated in aquaculture due to its nutritional value and the ability to produce valuable chemical compounds, such as pigments (zeaxanthin, astaxanthin...) and polyunsaturated fatty acids (EPA). Commercial exploitation needs high cell densities but the low growth rate and the small size of cells are practical difficulties. To increase biomass concentration the positive effect of several factors was evident: (i) pH[approximate]8 control (with dilute Tris-HCl buffer); (ii) the continuous illumination (no evidence of photo-inhibition was observed); (iii) a quite large temperature range (25±5 °C); (iv) the presence of organic carbon source (with the danger of contamination); (v) the presence of urea as an additional nitrogen source (10 mM); (vi) a small air flow rate with large bubbles can be more efficient for CO2 mass transfer (associated to reduced shearing).http://www.sciencedirect.com/science/article/B6VRM-492W13D-4/1/d65b11cf23c3d0795406c391c335446
Sharp lines in the absorption edge of EuTe and PbEuTe in high magnetic fields
The optical absorption spectra in the region of the \fd transition energies
of epitaxial layers of of EuTe and \PbEuTe, grown by molecular beam epitaxy,
were studied using circularly polarized light, in the Faraday configuration.
Under \sigmam polarization a sharp symmetric absorption line (full width at
half-maximum 0.041 eV) emerges at the low energy side of the band-edge
absorption, for magnetic fields intensities greater than 6 T. The absorption
line shows a huge red shift (35 meV/T) with increasing magnetic fields. The
peak position of the absorption line as a function of magnetic field is
dominated by the {\em d-f} exchange interaction of the excited electron and the
\Euion spins in the lattice. The {\em d-f} exchange interaction energy was
estimated to be eV. In \PbEuTe the same absorption line
is detected, but it is broader, due to alloy disorder, indicating that the
excitation is localized within a finite radius. From a comparison of the
absorption spectra in EuTe and \PbEuTe the characteristic radius of the
excitation is estimated to be \AA.Comment: Journal of Physics: Condensed Matter (2004, at press
The incidence of cancer and potential role of sirolimus immunosuppression conversion on mortality among a single-center renal transplantation cohort of 1,816 patients
INTRODUCTION:
The chronic use of immunosuppressive drugs in renal transplant recipients increases the risk of developing de novo malignancies. Herein we analyze the incidence of de novo tumors and the potential role of sirolimus to improve cancer-specific survival among a cohort at a single center.
METHODS:
This retrospective analysis of our 1,816 patients allografted between January 1983 and December 2009 sought subjects who developed de novo tumors. Epidemiological and clinical data were examined using Mann-Whitney and Pearson's chi-square or Fisher exact tests for statistical comparisons of continuous and categorical variables, respectively. Kaplan-Meier survival curves were used to determine cancer-specific survival according to type of neoplasia and immunosuppressive regimen, namely, conversion to sirolimus.
RESULTS:
One hundred patients (5.5%) were diagnosed with a de novo malignancy. The 110 different cancers were diagnosed at a median interval of 73 months after kidney transplantation. The overall cancer-specific survivals at 1 and 5 years after cancer diagnosis were 87.0% and 76.9%, respectively. The 15 patients converted to sirolimus showed no difference in survival.
CONCLUSION:
The observed frequencies of cancer in our center are consistent with the literature. Among our cohort, sirolimus did not significantly impact survival among subjects who had de novo malignancies
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