82 research outputs found
Hold on to your friends: dedicated chaperones of ribosomal proteins
Eukaryotic ribosomes are assembled from their components, the ribosomal RNAs and ribosomal proteins, in a tremendously complex, multi-step process, which primarily takes place in the nuclear compartment. Therefore, most ribosomal proteins have to travel from the cytoplasm to their incorporation site on pre-ribosomes within the nucleus. However, due to their particular characteristics, such as a highly basic amino acid composition and the presence of unstructured extensions, ribosomal proteins are especially prone to aggregation and degradation in their unassembled state, hence specific mechanisms must operate to ensure their safe delivery. Recent studies have uncovered a group of proteins, termed dedicated chaperones, specialized in accompanying and guarding individual ribosomal proteins. In this essay, we review how these dedicated chaperones utilize different folds to interact with their ribosomal protein clients and how they ensure their soluble expression and interconnect their intracellular transport with their efficient assembly into pre-ribosomes
A Compact Full-disk Solar Magnetograph based on miniaturization of GONG instrument
Designing compact instruments is the key for the scientific exploration by
smaller spacecrafts such as cubesats or by deep space missions. Such missions
require compact instrument designs to have minimal instrument mass. Here we
present a proof of concept for miniaturization of the Global Oscillation
Network Group GONG instrument. GONG instrument routinely obtains solar full
disk Doppler and magnetic field maps of the solar photosphere using Ni 676 nm
absorption line. A key concept for miniaturization of GONG optical design is to
replace the bulky Lyot filter with a narrow-band interference filter and reduce
the length of feed telescope. We present validation of the concept via
numerical modeling as well as by proof of concept observations.Comment: 13 pages, 6 figure
Assessing the impacts of shoreline hardening on beach response to hurricanes: Saint-Barthélemy, Lesser Antilles
International audienc
Magnetic Structure of an Erupting Filament
The full 3-D vector magnetic field of a solar filament prior to eruption is
presented. The filament was observed with the Facility Infrared
Spectropolarimeter at the Dunn Solar Telescope in the chromospheric He i line
at 10830 {\AA} on May 29 and 30, 2017. We inverted the spectropolarimetric
observations with the HAnle and ZEeman Light (HAZEL) code to obtain the
chromospheric magnetic field. A bimodal distribution of field strength was
found in or near the filament. The average field strength was 24 Gauss, but
prior to the eruption we find the 90th percentile of field strength was 435
Gauss for the observations on May 29. The field inclination was about 67 degree
from the solar vertical. The field azimuth made an angle of about 47 to 65
degree to the spine axis. The results suggest an inverse configuration
indicative of a flux rope topology. He i intensity threads were found to be
co-aligned with the magnetic field direction. The filament had a sinistral
configuration as expected for the southern hemisphere. The filament was stable
on May 29, 2017 and started to rise during two observations on May 30, before
erupting and causing a minor coronal mass ejection. There was no obvious change
of the magnetic topology during the eruption process. Such information on the
magnetic topology of erupting filaments could improve the prediction of the
geoeffectiveness of solar storms
Velocities of an Erupting Filament
Solar filaments exist as stable structures for extended periods of time before many of them form the core of a coronal mass ejection (CME). We examine the properties of an erupting filament on 2017 May 29–30 with high-resolution He i 10830 Å and Hα spectra from the Dunn Solar Telescope, full-disk Dopplergrams of He i 10830 Å from the Chromospheric Telescope, and EUV and coronograph data from SDO and STEREO. Pre-eruption line-of-sight velocities from an inversion of He i with the HAZEL code exhibit coherent patches of 5 Mm extent that indicate counter-streaming and/or buoyant behavior. During the eruption, individual, aligned threads appear in the He i velocity maps. The distribution of velocities evolves from Gaussian to strongly asymmetric. The maximal optical depth of He i 10830 Å decreased from τ = 1.75 to 0.25, the temperature increased by 13 kK, and the average speed and width of the filament increased from 0 to 25 km s−1 and 10 to 20 Mm, respectively. All data sources agree that the filament rose with an exponential acceleration reaching 7.4 m s−2 that increased to a final velocity of 430 km s−1 at 22:24 UT; a CME was associated with this filament eruption. The properties during the eruption favor a kink/torus instability, which requires the existence of a flux rope. We conclude that full-disk chromospheric Dopplergrams can be used to trace the initial phase of on-disk filament eruptions in real time, which might potentially be useful for modeling the source of any subsequent CMEs
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