2,828 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
Microoptical Realization of Arrays of Selectively Addressable Dipole Traps: A Scalable Configuration for Quantum Computation with Atomic Qubits
We experimentally demonstrate novel structures for the realisation of
registers of atomic qubits: We trap neutral atoms in one and two-dimensional
arrays of far-detuned dipole traps obtained by focusing a red-detuned laser
beam with a microfabricated array of microlenses. We are able to selectively
address individual trap sites due to their large lateral separation of 125 mu
m. We initialize and read out different internal states for the individual
sites. We also create two interleaved sets of trap arrays with adjustable
separation, as required for many proposed implementations of quantum gate
operations
Gamma-ray probe of cosmic-ray pressure in galaxy clusters and cosmological implications
Cosmic rays produced in cluster accretion and merger shocks provide pressure
to the intracluster medium (ICM) and affect the mass estimates of galaxy
clusters. Although direct evidence for cosmic-ray ions in the ICM is still
lacking, they produce gamma-ray emission through the decay of neutral pions
produced in their collisions with ICM nucleons. We investigate the capability
of the Gamma-ray Large Area Space Telescope (GLAST) and imaging atmospheric
Cerenkov telescopes (IACTs) for constraining the cosmic-ray pressure
contribution to the ICM. We show that GLAST can be used to place stringent
upper limits, a few per cent for individual nearby rich clusters, on the ratio
of pressures of the cosmic rays and thermal gas. We further show that it is
possible to place tight (<~10%) constraints for distant (z <~ 0.25) clusters in
the case of hard spectrum, by stacking signals from samples of known clusters.
The GLAST limits could be made more precise with the constraint on the
cosmic-ray spectrum potentially provided by IACTs. Future gamma-ray
observations of clusters can constrain the evolution of cosmic-ray energy
density, which would have important implications for cosmological tests with
upcoming X-ray and Sunyaev-Zel'dovich effect cluster surveys.Comment: 12 pages, 5 figures; extended discussions; accepted by MNRA
Effect of Magnetization Inhomogeneity on Magnetic Microtraps for Atoms
We report on the origin of fragmentation of ultracold atoms observed on a
permanent magnetic film atom chip. A novel technique is used to characterize
small spatial variations of the magnetic field near the film surface using
radio frequency spectroscopy of the trapped atoms. Direct observations indicate
the fragmentation is due to a corrugation of the magnetic potential caused by
long range inhomogeneity in the film magnetization. A model which takes into
account two-dimensional variations of the film magnetization is consistent with
the observations.Comment: 4 pages, 4 figure
Prioritising urban green spaces using accessibility and quality as criteria
Urban green spaces are a critical component of cities, providing environmental, social, cultural, and economic benefits. To support smart(er) decisions by city planners and managers, this study aims to investigate how open data sources could be integrated into urban green space management. Specifically, it proposes a novel GIS-based method to prioritise urban green space in a resource-constraint scenario so that social benefits are maximised. To quantify the social benefits, the methodology is based on the WHO indicator, which recommends access to at least 0.5-1 ha of green space within 300 metres\u27 linear distance to all the city residents. The approach assigns each urban green space an \u27accessibility score\u27 based on its significance in the city, and a \u27quality score\u27 based on its performance on different quality parameters (size, greenness, quietness, and safety). Urban green spaces are ranked with respect to these two scores, enabling to prioritise spaces under resource constraints such as water shortage, limited staff, or budget. This approach is demonstrated through a case study on a mid-size German city and is transferable to other cities worldwide with varying weightage factors
Resistência a penetração e produção de azevém no entorno de cochos em integração lavoura-pecuária.
Magnetic field reversals in an experimental turbulent dynamo
We report the first experimental observation of reversals of a dynamo field
generated in a laboratory experiment based on a turbulent flow of liquid
sodium. The magnetic field randomly switches between two symmetric solutions B
and -B. We observe a hierarchy of time scales similar to the Earth's magnetic
field: the duration of the steady phases is widely distributed, but is always
much longer than the time needed to switch polarity. In addition to reversals
we report excursions. Both coincide with minima of the mechanical power driving
the flow. Small changes in the flow driving parameters also reveal a large
variety of dynamo regimes.Comment: 5 pages, 4 figure
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