5,133 research outputs found
Width of Sunspot Generating Zone and Reconstruction of Butterfly Diagram
Based on the extended Greenwich-NOAA/USAF catalogue of sunspot groups it is
demonstrated that the parameters describing the latitudinal width of the
sunspot generating zone (SGZ) are closely related to the current level of solar
activity, and the growth of the activity leads to the expansion of SGZ. The
ratio of the sunspot number to the width of SGZ shows saturation at a certain
level of the sunspot number, and above this level the increase of the activity
takes place mostly due to the expansion of SGZ. It is shown that the mean
latitudes of sunspots can be reconstructed from the amplitudes of solar
activity. Using the obtained relations and the group sunspot numbers by Hoyt
and Schatten (1998), the latitude distribution of sunspot groups ("the Maunder
butterfly diagram") for the 18th and the first half of the 19th centuries is
reconstructed and compared with historical sunspot observations.Comment: 16 pages, 11 figures; accepted by Solar Physics; the final
publication will be available at www.springerlink.co
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Intermediate progenitors support migration of neural stem cells into dentate gyrus outer neurogenic niches.
The hippocampal dentate gyrus (DG) is a unique brain region maintaining neural stem cells (NCSs) and neurogenesis into adulthood. We used multiphoton imaging to visualize genetically defined progenitor subpopulations in live slices across key stages of mouse DG development, testing decades old static models of DG formation with molecular identification, genetic-lineage tracing, and mutant analyses. We found novel progenitor migrations, timings, dynamic cell-cell interactions, signaling activities, and routes underlie mosaic DG formation. Intermediate progenitors (IPs, Tbr2+) pioneered migrations, supporting and guiding later emigrating NSCs (Sox9+) through multiple transient zones prior to converging at the nascent outer adult niche in a dynamic settling process, generating all prenatal and postnatal granule neurons in defined spatiotemporal order. IPs (Dll1+) extensively targeted contacts to mitotic NSCs (Notch active), revealing a substrate for cell-cell contact support during migrations, a developmental feature maintained in adults. Mouse DG formation shares conserved features of human neocortical expansion
Turbulent viscosity in clumpy accretion disks II supernova driven turbulence in the Galaxy
An analytical model for a turbulent clumpy gas disk is presented where
turbulence is maintained by the energy input due to supernovae. Expressions for
the disk parameters, global filling factors, molecular fractions, and star
formation rates are given as functions of the Toomre parameter , the ratio
between the cloud size and the turbulent driving length scale , the
mass accretion rate within the disk , the constant of molecule
formation , the disk radius, the angular velocity, and its radial
derivative. Two different cases are investigated: a dominating stellar disk and
a self-gravitating gas disk in direction. The turbulent driving wavelength
is determined in a first approach by energy flux conservation, i.e. the
supernovae energy input is transported by turbulence to smaller scales where it
is dissipated. The results are compared to those of a fully gravitational
model. For Q=1 and both models are consistent with each other. In a
second approach the driving length scale is directly determined by the size of
supernovae remnants. Both models are applied to the Galaxy and can reproduce
its integrated and local gas properties. The influence of thermal and magnetic
pressure on the disk structure is investigated. We infer and
for the Galaxy.Comment: 15 pages with 10 figures. Accepted for publication in A&
A renormalization group invariant scalar glueball operator in the (Refined) Gribov-Zwanziger framework
This paper presents a complete algebraic analysis of the renormalizability of
the operator in the Gribov-Zwanziger (GZ) formalism as
well as in the Refined Gribov-Zwanziger (RGZ) version. The GZ formalism offers
a way to deal with gauge copies in the Landau gauge. We explicitly show that
mixes with other gauge variant operators, and we determine
the mixing matrix to all orders, thereby only using algebraic arguments.
The mixing matrix allows us to uncover a renormalization group invariant
including the operator . With this renormalization group
invariant, we have paved the way for the study of the lightest scalar glueball
in the GZ formalism. We discuss how the soft breaking of the BRST symmetry of
the GZ action can influence the glueball correlation function. We expect
non-trivial mass scales, inherent to the GZ approach, to enter the pole
structure of this correlation function.Comment: 27 page
Human hippocampal neurogenesis drops sharply in children to undetectable levels in adults.
New neurons continue to be generated in the subgranular zone of the dentate gyrus of the adult mammalian hippocampus. This process has been linked to learning and memory, stress and exercise, and is thought to be altered in neurological disease. In humans, some studies have suggested that hundreds of new neurons are added to the adult dentate gyrus every day, whereas other studies find many fewer putative new neurons. Despite these discrepancies, it is generally believed that the adult human hippocampus continues to generate new neurons. Here we show that a defined population of progenitor cells does not coalesce in the subgranular zone during human fetal or postnatal development. We also find that the number of proliferating progenitors and young neurons in the dentate gyrus declines sharply during the first year of life and only a few isolated young neurons are observed by 7 and 13 years of age. In adult patients with epilepsy and healthy adults (18-77 years; n = 17 post-mortem samples from controls; n = 12 surgical resection samples from patients with epilepsy), young neurons were not detected in the dentate gyrus. In the monkey (Macaca mulatta) hippocampus, proliferation of neurons in the subgranular zone was found in early postnatal life, but this diminished during juvenile development as neurogenesis decreased. We conclude that recruitment of young neurons to the primate hippocampus decreases rapidly during the first years of life, and that neurogenesis in the dentate gyrus does not continue, or is extremely rare, in adult humans. The early decline in hippocampal neurogenesis raises questions about how the function of the dentate gyrus differs between humans and other species in which adult hippocampal neurogenesis is preserved
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