46 research outputs found
Energy Estimation of Cosmic Rays with the Engineering Radio Array of the Pierre Auger Observatory
The Auger Engineering Radio Array (AERA) is part of the Pierre Auger
Observatory and is used to detect the radio emission of cosmic-ray air showers.
These observations are compared to the data of the surface detector stations of
the Observatory, which provide well-calibrated information on the cosmic-ray
energies and arrival directions. The response of the radio stations in the 30
to 80 MHz regime has been thoroughly calibrated to enable the reconstruction of
the incoming electric field. For the latter, the energy deposit per area is
determined from the radio pulses at each observer position and is interpolated
using a two-dimensional function that takes into account signal asymmetries due
to interference between the geomagnetic and charge-excess emission components.
The spatial integral over the signal distribution gives a direct measurement of
the energy transferred from the primary cosmic ray into radio emission in the
AERA frequency range. We measure 15.8 MeV of radiation energy for a 1 EeV air
shower arriving perpendicularly to the geomagnetic field. This radiation energy
-- corrected for geometrical effects -- is used as a cosmic-ray energy
estimator. Performing an absolute energy calibration against the
surface-detector information, we observe that this radio-energy estimator
scales quadratically with the cosmic-ray energy as expected for coherent
emission. We find an energy resolution of the radio reconstruction of 22% for
the data set and 17% for a high-quality subset containing only events with at
least five radio stations with signal.Comment: Replaced with published version. Added journal reference and DO
Measurement of the Radiation Energy in the Radio Signal of Extensive Air Showers as a Universal Estimator of Cosmic-Ray Energy
We measure the energy emitted by extensive air showers in the form of radio
emission in the frequency range from 30 to 80 MHz. Exploiting the accurate
energy scale of the Pierre Auger Observatory, we obtain a radiation energy of
15.8 \pm 0.7 (stat) \pm 6.7 (sys) MeV for cosmic rays with an energy of 1 EeV
arriving perpendicularly to a geomagnetic field of 0.24 G, scaling
quadratically with the cosmic-ray energy. A comparison with predictions from
state-of-the-art first-principle calculations shows agreement with our
measurement. The radiation energy provides direct access to the calorimetric
energy in the electromagnetic cascade of extensive air showers. Comparison with
our result thus allows the direct calibration of any cosmic-ray radio detector
against the well-established energy scale of the Pierre Auger Observatory.Comment: Replaced with published version. Added journal reference and DOI.
Supplemental material in the ancillary file
Structural Analysis of the 42 kDa Parvulin of Trypanosoma brucei
Trypanosoma brucei is a unicellular eukaryotic parasite, which causes the African sleeping sickness in humans. The recently discovered trypanosomal protein Parvulin 42 (TbPar42) plays a key role in parasite cell proliferation. Homologues of this two-domain protein are exclusively found in protozoa species. TbPar42 exhibits an N-terminal forkhead associated (FHA)-domain and a peptidyl-prolyl-cis/trans-isomerase (PPIase) domain, both connected by a linker. Using NMR and X-ray analysis as well as activity assays, we report on the structures of the single domains of TbPar42, discuss their intra-molecular interplay, and give some initial hints as to potential cellular functions of the protein
Synthesis of 20-Membered Macrocyclic Pseudo-Natural Products Yields Inducers of LC3 Lipidation
Design and synthesis of pseudo-natural products (PNPs) through recombination of natural product (NP) fragments in unprecedented arrangements enables the discovery of novel biologically relevant chemical matter. With a view to wider coverage of NP-inspired chemical and biological space, we describe the combination of this principle with macrocycle formation. PNP-macrocycles were synthesized efficiently in a stereoselective one-pot procedure including the 1,3-dipolar cycloadditions of different dipolarophiles with dimeric cinchona alkaloid-derived azomethine ylides formed in situ. The 20-membered bis-cycloadducts embody 18 stereocenters and an additional fragment-sized NP-structure. After further functionalization, a collection of 163 macrocyclic PNPs was obtained. Biological investigation revealed potent inducers of the lipidation of the microtubule associated protein 1 light chain 3 (LC3) protein, which plays a prominent role in various autophagy-related processes