7,926 research outputs found
Universal dissipation scaling for non-equilibrium turbulence
It is experimentally shown that the non-classical high Reynolds number energy
dissipation behaviour, ,
observed during the decay of fractal square grid-generated turbulence is also
manifested in decaying turbulence originating from various regular grids. For
sufficiently high values of the global Reynolds numbers , .Comment: 5 pages, 6 figure
Polarization squeezing of light by single passage through an atomic vapor
We have studied relative-intensity fluctuations for a variable set of
orthogonal elliptic polarization components of a linearly polarized laser beam
traversing a resonant Rb vapor cell. Significant polarization squeezing
at the threshold level (-3dB) required for the implementation of several
continuous variables quantum protocols was observed. The extreme simplicity of
the setup, based on standard polarization components, makes it particularly
convenient for quantum information applications.Comment: Revised version. Minor changes. four pages, three figure
Optimal irreversible stimulated emission
We studied the dynamics of an initially inverted atom in a semi-infinite
waveguide, in the presence of a single propagating photon. We show that atomic
relaxation is enhanced by a factor of 2, leading to maximal bunching in the
output field. This optimal irreversible stimulated emission is a novel
phenomenon that can be observed with state-of-the-art solid-state atoms and
waveguides. When the atom interacts with two one-dimensional electromagnetic
environments, the preferential emission in the stimulated field can be
exploited to efficiently amplify a classical or a quantum state.Comment: 9 pages, 6 figure
Numerical investigation of the quantum fluctuations of optical fields transmitted through an atomic medium
We have numerically solved the Heisenberg-Langevin equations describing the
propagation of quantized fields through an optically thick sample of atoms. Two
orthogonal polarization components are considered for the field and the
complete Zeeman sublevel structure of the atomic transition is taken into
account. Quantum fluctuations of atomic operators are included through
appropriate Langevin forces. We have considered an incident field in a linearly
polarized coherent state (driving field) and vacuum in the perpendicular
polarization and calculated the noise spectra of the amplitude and phase
quadratures of the output field for two orthogonal polarizations. We analyze
different configurations depending on the total angular momentum of the ground
and excited atomic states. We examine the generation of squeezing for the
driving field polarization component and vacuum squeezing of the orthogonal
polarization. Entanglement of orthogonally polarized modes is predicted. Noise
spectral features specific of (Zeeman) multi-level configurations are
identified.Comment: 12 pages 9 figures. Submitted to Physical Review
Temporal control of epigenetic centromere specification
All living organisms require accurate mechanisms to faithfully inherit their genetic material during cell division. The centromere is a unique locus on each chromosome that supports a multiprotein structure called the kinetochore. During mitosis, the kinetochore is responsible for connecting chromosomes to spindle microtubules, allowing faithful segregation of the duplicated genome. In most organisms, centromere position and function is not defined by the local DNA sequence context but rather by an epigenetic chromatin-based mechanism. Centromere protein A (CENP-A) is central to this process, as chromatin assembled from this histone H3 variant is essential for assembly of the centromere complex, as well as for its epigenetic maintenance. As a major determinant of centromere function, CENP-A assembly requires tight control, both in its specificity for the centromere and in timing of assembly. In the last few years, there have been several new insights into the molecular mechanism that allow this process to occur. We will review these here and discuss the general implications of the mechanism of cell cycle coupling of centromere inheritance.FCT fellowships: (SFRH/BPD/69115/2010, SFRH/BD/33219/2007); FCT grants: (BIA-BCM/100557/2008, BIA-PRO/100537/2008);Fundação Calouste Gulbenkian; European Commission FP7 programme; EMBO installation grant
Malária Grave — Um Caso Clínico
Descreve-se um caso de malária grave por Plasmodium falciparum numa criança de raça negra, de 5 anos de idade, residente
em Angola até 2 semanas antes do internamento. Apesar da terapêutica com quinino i.v. o quadro evoluiu com falência multiorgânica, nomeadamente coma, insuficiência renal, necrose hepática, diátese hemorrágica e rabdomiólise. Foi necessário instituir ventilação
mecânica e na terapêutica de suporte recorreu-se à administração de derivados plasmáticos, aminas vasoactivas e diuréticos em altas doses, tendo havido regressão do quadro clínico. Discutem-se as complicações bem como os factores de mau prognóstico presentes neste caso
Thermal restraint and fire resistance of columns
A proposal is made, based on the results of a series of tests and calculations, with the aim of being used as a simple method to correct the value of the critical temperature of steel columns free to elongate, in order to take into account the restraint effect of the structure to which they belong in a practical situation. To better illustrate the possible types of behaviour of heated steel columns with elastic restraint to the thermal elongation, and the reasons why the critical temperature of axially loaded slender steel columns with thermal restraint can sometimes be lower than the critical temperature of the same columns free to elongate, a simple model is presented and used in a qualitative analysis.http://www.sciencedirect.com/science/article/B6V37-46WW50B-1/1/139a30367738460772843d1279c4c32
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