967 research outputs found
Magnetic field intensification: comparison of 3D MHD simulations with Hinode/SP results
Recent spectro-polarimetric observations have provided detailed measurements
of magnetic field, velocity and intensity during events of magnetic field
intensification in the solar photosphere. We consider the temporal evolution of
the relevant physical quantities for three cases of magnetic field
intensification in a numerical simulation. We determine the evolution of the
intensity, magnetic flux density and zero-crossing velocity derived from the
synthetic Stokes parameters by taking into account the spectral and spatial
resolution of the spectropolarimeter (SP) on board Hinode. The three events
considered show a similar evolution: advection of magnetic flux to a granular
vertex, development of a strong downflow, evacuation of the magnetic feature,
increase of the field strength and the appearance of the bright point. We find
that synthetic and real observations are qualitatively consistent and, for one
of the cases considered, agree very well also quantitatively. The effect of
finite resolution (spatial smearing) is most pronounced in the case of small
features, for which the synthetic Hinode/SP observations miss the bright point
formation and also the high-velocity downflows during the formation of the
smaller magnetic features.Comment: accepted in A&
Mesogranular structure in a hydrodynamical simulation
We analyse mesogranular flow patterns in a three-dimensional hydrodynamical
simulation of solar surface convection in order to determine its
characteristics. We calculate divergence maps from horizontal velocities
obtained with the Local Correlation Tracking (LCT) method. Mesogranules are
identified as patches of positive velocity divergence. We track the
mesogranules to obtain their size and lifetime distributions. We vary the
analysis parameters to verify if the pattern has characteristic scales. The
characteristics of the resulting flow patterns depend on the averaging time and
length used in the analysis. We conclude that the mesogranular patterns do not
exhibit intrinsic length and time scales
C-terminal fusion of eGFP to the bradykinin B-2 receptor strongly affects down-regulation but not receptor internalization or signaling
A functional comparison was made between the wildtype bradykinin B, receptor (B(2)wt) and the chimera B(2)eGFP (enhanced green-fluorescent protein fused to the C-terminus of B(2)Wt), both stably expressed in HEK 293 cells. There was almost no difference in terms of ligand-inducible receptor phosphorylation and internalization, signal transduction (accumulation of inositol phosphates) or expression and affinity. However, stimulation for up to 8 h with 10 mu M bradykinin (BK) resulted in a strong decrease in surface receptors (by 60% within 5 h) in B(2)Wt, but not in B(2)eGFP. When the expression levels of both constructs where comparably reduced using a weaker promoter, long-term stimulation resulted in a reduction in surface receptors for B(2)wt(low) to less than 20% within 1 h, whereas the chimera B(2)eGFP(low) still displayed 50% binding activity after 2 h. A 1-h incubation in the absence of BK resulted in a recovery of 60% of the binding in B(2)wt(low) after 1-h stimulation with BK, but of only 20% after 7-h stimulation. In contrast, B(2)eGFP(low) levels were restored to more than 70%, even after 7-h stimulation. These data indicate that although the fusion of eGFP to B(2)wt does not affect its ligand-induced internalization, it strongly reduces the down-regulation, most likely by promoting receptor recycling over degradation
Management Attitudes towards HRM Practices and Works Council Presence in German SMEs
This paper examines the impact of management attitudes towards human resource
management (HRM) practices on the presence of works councils in German small
and medium-sized enterprises (SMEs). Based on a survey among executives of
German SMEs, the key result of a logit regression analysis is that managers’
attitudes towards key HRM practices have a strong impact on the prevalence of
the works council in German SMEs. In particular, positive management attitudes
towards individual employee participation and direct supervision seem to be
detrimental for the institutionalization of works councils. The results
suggest that there is more diversity and management choice regarding the
institutions of industrial relations than generally expected in the case of
German firms
Molecular Basis for poly(A) RNP Architecture and Recognition by the Pan2-Pan3 Deadenylase
The stability of eukaryotic mRNAs is dependent on a ribonucleoprotein (RNP) complex of poly(A)-binding proteins (PABPC1/Pab1) organized on the poly(A) tail. This poly(A) RNP not only protects mRNAs from premature degradation but also stimulates the Pan2-Pan3 deadenylase complex to catalyze the first step of poly(A) tail shortening. We reconstituted this process in vitro using recombinant proteins and show that Pan2-Pan3 associates with and degrades poly(A) RNPs containing two or more Pab1 molecules. The cryo-EM structure of Pan2-Pan3 in complex with a poly(A) RNP composed of 90 adenosines and three Pab1 protomers shows how the oligomerization interfaces of Pab1 are recognized by conserved features of the deadenylase and thread the poly(A) RNA substrate into the nuclease active site. The structure reveals the basis for the periodic repeating architecture at the 3' end of cytoplasmic mRNAs. This illustrates mechanistically how RNA-bound Pab1 oligomers act as rulers for poly(A) tail length over the mRNAs' lifetime.We would like to thank ... the MPIB cryo-EM, and core facilities ..
The intensity contrast of solar granulation: comparing Hinode SP results with MHD simulations
The contrast of granulation is an important quantity characterizing solar
surface convection. We compare the intensity contrast at 630 nm, observed using
the Spectro-Polarimeter (SP) aboard the Hinode satellite, with the 3D radiative
MHD simulations of V{\"o}gler & Sch{\"u}ssler (2007). A synthetic image from
the simulation is degraded using a theoretical point-spread function of the
optical system, and by considering other important effects. The telescope
aperture and the obscuration by the secondary mirror and its attachment spider,
reduce the simulated contrast from 14.4 % to 8.5 %. A slight effective defocus
of the instrument brings the simulated contrast down to 7.5 %, close to the
observed value of 7.0 %. A proper consideration of the effects of the optical
system and a slight defocus, lead to sufficient degradation of the synthetic
image from the MHD simulation, such that the contrast reaches almost the
observed value. The remaining small discrepancy can be ascribed to straylight
and slight imperfections of the instrument, which are difficult to model.
Hence, Hinode SP data are consistent with a granulation contrast which is
predicted by 3D radiation MHD simulations.Comment: 5 pages, 4 figures, to be published in A&
A comparison of measured and simulated solar network contrast
Long-term trends in the solar spectral irradiance are important to determine
the impact on Earth's climate. These long-term changes are thought to be caused
mainly by changes in the surface area covered by small-scale magnetic elements.
The direct measurement of the contrast to determine the impact of these
small-scale magnetic elements is, however, limited to a few wavelengths, and
is, even for space instruments, affected by scattered light and instrument
defocus. In this work we calculate emergent intensities from 3-D simulations of
solar magneto-convection and validate the outcome by comparing with
observations from Hinode/SOT. In this manner we aim to construct the contrast
at wavelengths ranging from the NUV to the FIR.Comment: Proceedings paper, IAU XXVII, Symposium 264, 3 page
Suppression of small scale dynamo action by an imposed magnetic field
Non-helical hydromagnetic turbulence with an externally imposed magnetic
field is investigated using direct numerical simulations. It is shown that the
imposed magnetic field lowers the spectral magnetic energy in the inertial
range. This is explained by a suppression of the small scale dynamo. At large
scales, however, the spectral magnetic energy increases with increasing imposed
field strength for moderately strong fields, and decreases only slightly for
even stronger fields. The presence of Alfven waves is explicitly confirmed by
monitoring the evolution of magnetic field and velocity at one point. The
frequency omega agrees with vA k1, where vA is the Alfven speed and k1 is the
smallest wavenumber in the box.Comment: Final version (7 pages
MpTCP1 controls cell proliferation and redox processes in Marchantia polymorpha
TCP transcription factors are key regulators of angiosperm cell proliferation processes. It is unknown whether their regulatory growth capacities are conserved across land plants, which we examined in liverworts, one of the earliest diverging land plant lineages. We generated knockout mutants for MpTCP1, the single TCP‐P clade gene in Marchantia polymorpha, and characterized its function conducting cell proliferation and morphological analyses as well as mRNA expression, transcriptome, chemical and DNA binding studies. Mptcp1ge lines show a reduced vegetative thallus growth and extra tissue formation in female reproductive structures. Additionally, mutant plants reveal increased H2O2 levels and an enhanced pigmentation in the thallus caused by formation of secondary metabolites, such as aminochromes. MpTCP1 proteins interact redox‐dependently with DNA and regulate the expression of a comprehensive redox network, comprising enzymes involved in H2O2 metabolism. MpTCP1 regulates Marchantia growth context‐dependently. Redox sensitivity of the DNA binding capacity of MpTCP1 proteins provides a mechanism to respond to altered redox conditions. Our data suggest that MpTCP1 activity could thereby have contributed to diversification of land plant morphologies and to adaptations to abiotic and biotic challenges, experienced by liverworts during early land plant colonization
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