3,113 research outputs found
Positional changes of pericentromeric heterochromatin and nucleoli in postmitotic Purkinje cells during murine cerebellum development
Previous studies revealed changes of pericentromeric heterochromatin arrangements in postmitotic Purkinje cells (PCs) during postnatal development in the mouse cerebellum (Manuelidis, 1985; Martou and De Boni, 2000). Here, we performed vibratome sections of mouse cerebellum (vermis) at P0 (day of birth), at various stages of the postnatal development (P2-P21), as well as in very young (P28) and 17-months-old adults. FISH was carried out on these sections with major mouse satellite DNA in combination with immunostaining of the nucleolar protein B23 (nucleophosmin). Laser confocal microscopy, 3D reconstructions and quantitative image analysis were employed to describe changes in the number and topology of chromocenters and nucleoli. At all stages of postnatal PC development heterochromatin clusters were typically associated either with nucleoli or with the nuclear periphery, while non-associated clusters were rare (<1% at P0 to P21 and about 3% in adult stages). At P0, about 2-4 nucleoli and 7-8 pericentromeric heterochromatin clusters were variably located within PC nuclei. The relative volume of heterochromatin clusters associated with the nucleoli (about 50%) was roughly equal to the volume of clusters associated with the nuclear periphery. Positional changes of both nucleoli and centromeres towards the nuclear center occurred between P0 and P6. At P6 the average number of chromocenters per PC nucleus had decreased to about five. In agreement with previous studies, one or occasionally two nucleoli were noted at the nuclear center surrounded by major perinucleolar heterochromatin clusters. The relative volume of these perinucleolar clusters increased to about 84%, while the volume of clusters in the nuclear periphery decreased to about 15%. At subsequent postnatal stages, the arrangement of most pericentromeric heterochromatin around a central nucleolus was maintained. In adult animals, however, we observed a partial redistribution of heterochromatin towards the nuclear periphery. The average total number of pericentromeric heterochromatin signals increased again to about ten. The volume of heterochromatin associated with the nuclear periphery roughly doubled (30%), while the volume of the perinucleolar heterochromatin decreased correspondingly. Copyright (C) 2004 S. Karger AG, Basel
Melting dynamics of large ice balls in a turbulent swirling flow
We study the melting dynamics of large ice balls in a turbulent von Karman
flow at very high Reynolds number. Using an optical shadowgraphy setup, we
record the time evolution of particle sizes. We study the heat transfer as a
function of the particle scale Reynolds number for three cases: fixed ice balls
melting in a region of strong turbulence with zero mean flow, fixed ice balls
melting under the action of a strong mean flow with lower fluctuations, and ice
balls freely advected in the whole flow. For the fixed particles cases, heat
transfer is observed to be much stronger than in laminar flows, the Nusselt
number behaving as a power law of the Reynolds number of exponent 0.8. For
freely advected ice balls, the turbulent transfer is further enhanced and the
Nusselt number is proportional to the Reynolds number. The surface heat flux is
then independent of the particles size, leading to an ultimate regime of heat
transfer reached when the thermal boundary layer is fully turbulent
Spin-orbit coupling and phase-coherence in InAs nanowires
We investigated the magnetotransport of InAs nanowires grown by selective
area metal-organic vapor phase epitaxy. In the temperature range between 0.5
and 30 K reproducible fluctuations in the conductance upon variation of the
magnetic field or the back-gate voltage are observed, which are attributed to
electron interference effects in small disordered conductors. From the
correlation field of the magnetoconductance fluctuations the phase-coherence
length l_phi is determined. At the lowest temperatures l_phi is found to be at
least 300 nm, while for temperatures exceeding 2 K a monotonous decrease of
l_phi with temperature is observed. A direct observation of the weak
antilocalization effect indicating the presence of spin-orbit coupling is
masked by the strong magnetoconductance fluctuations. However, by averaging the
magnetoconductance over a range of gate voltages a clear peak in the
magnetoconductance due to the weak antilocalization effect was resolved. By
comparison of the experimental data to simulations based on a recursive
two-dimensional Green's function approach a spin-orbit scattering length of
approximately 70 nm was extracted, indicating the presence of strong spin-orbit
coupling.Comment: 8 pages, 7 figure
Resistência a penetração e produção de azevém no entorno de cochos em integração lavoura-pecuária.
Variabilidade espacial em sistemas de integração lavoura-pecuária: desafios para o manejo sĂtio-especĂfico.
Variabilidade espacial em sistemas de integração lavoura-pecuária: desafios para o manejo sĂtio-especĂfico.
Enhancement of Be and Mg incorporation in wurtzite quaternary BeMgZnO alloys with up to 5.1 eV optical bandgap
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