Exploration of 10Be ice core records using a climatological model approach: Cosmogenic production versus climate variability

Ice core records of 10Be basically offer a wide range of applications in climate research. However, atmospheric transport and deposition processes still hamper their straightforward interpretation. This work aims at establishing a climatological, data-based model attempt which allows for the first quantitative simulation of 10Be ice concentration on a time scale of several 10kyr. To this end, a global atmospheric multi-box model is configured for the simulation of aerosol-borne radionuclides using extensive observations of natural and artificial nuclides. Validation with short-lived 7Be reveals that the model is capable to simulate its spatio-temporal distribution in the global atmosphere, thereby providing insight into the respective circulation of 10Be. To simulate 10Be ice core records, the model is coupled to a basic air-firn-transfer module based on spatial 10Be variations in polar ice. The model results, driven by precipitation/accumulation rate changes as well as solar and geomagnetic activity, closely reproduce the main features of observations on the Holocene and 75kyr timescale. Regarding the latter, climate-related accumulation rate changes dominate the ice concentration imposing variations of up to 300%. In contrast, incomplete atmospheric mixing of 10Be dampens the geomagnetic modulation of 10Be at polar sites by up to 50% compared to the global atmospheric 10Be inventory. These findings basically challenge the use of ice core 10Be as proxy for past geomagnetic activity

Glutathione-conjugating and membrane-remodeling activity of GDAP1 relies on amphipathic C-terminal domain

Mutations in the ganglioside-induced differentiation associated protein 1 (GDAP1) cause severe peripheral motor and sensory neuropathies called Charcot-Marie-Tooth disease. GDAP1 expression induces fission of mitochondria and peroxisomes by a currently elusive mechanism, while disease causing mutations in GDAP1 impede the protein’s role in mitochondrial dynamics. In silico analysis reveals sequence similarities of GDAP1 to glutathione S-transferases (GSTs). However, a proof of GST activity and its possible impact on membrane dynamics are lacking to date. Using recombinant protein, we demonstrate for the first time theta-class-like GST activity for GDAP1, and it’s activity being regulated by the C-terminal hydrophobic domain 1 (HD1) of GDAP1 in an autoinhibitory manner. Moreover, we show that the HD1 amphipathic pattern is required to induce membrane dynamics by GDAP1. As both, fission and GST activities of GDAP1, are critically dependent on HD1, we propose that GDAP1 undergoes a molecular switch, turning from a pro-fission active to an auto-inhibited inactive conformation.ISSN:2045-232

Atomic resolution mapping of localized phonon modes at grain boundaries

Phonon scattering at grain boundaries (GBs) is significant in controlling nanoscale device thermal conductivity. However, GBs could also act as waveguides for selected modes. To measure localized GB phonon modes, meV energy resolution is needed with sub-nm spatial resolution. Using monochromated electron energy loss spectroscopy (EELS) in the scanning transmission electron microscope (STEM) we have mapped the 60 meV optic mode across GBs in silicon at atomic resolution and compared it to calculated phonon densities of states (DOS). The intensity is strongly reduced at GBs characterised by the presence of five- and seven-fold rings where bond angles differ from the bulk. The excellent agreement between theory and experiment strongly supports the existence of localized phonon modes and thus of GBs acting as waveguides

Dosimetric precision of an ion beam tracking system

<p>Abstract</p> <p>Background</p> <p>Scanned ion beam therapy of intra-fractionally moving tumors requires motion mitigation. GSI proposed beam tracking and performed several experimental studies to analyse the dosimetric precision of the system for scanned carbon beams.</p> <p>Methods</p> <p>A beam tracking system has been developed and integrated in the scanned carbon ion beam therapy unit at GSI. The system adapts pencil beam positions and beam energy according to target motion.</p> <p>Motion compensation performance of the beam tracking system was assessed by measurements with radiographic films, a range telescope, a 3D array of 24 ionization chambers, and cell samples for biological dosimetry. Measurements were performed for stationary detectors and moving detectors using the beam tracking system.</p> <p>Results</p> <p>All detector systems showed comparable data for a moving setup when using beam tracking and the corresponding stationary setup. Within the target volume the mean relative differences of ionization chamber measurements were 0.3% (1.5% standard deviation, 3.7% maximum). Film responses demonstrated preserved lateral dose gradients. Measurements with the range telescope showed agreement of Bragg peak depth under motion induced range variations. Cell survival experiments showed a mean relative difference of -5% (-3%) between measurements and calculations within the target volume for beam tracking (stationary) measurements.</p> <p>Conclusions</p> <p>The beam tracking system has been successfully integrated. Full functionality has been validated dosimetrically in experiments with several detector types including biological cell systems.</p

Helium ions for radiotherapy? Physical and biological verifications of a novel treatment modality

Purpose: Modern facilities for actively scanned ion beam radiotherapy allow in principle the use of helium beams, which could present specific advantages, especially for pediatric tumors. In order to assess the potential use of these beams for radiotherapy, i.e., to create realistic treatment plans, the authors set up a dedicated He-4 beam model, providing base data for their treatment planning system TRiP98, and they have reported that in this work together with its physical and biological validations. Methods: A semiempirical beam model for the physical depth dose deposition and the production of nuclear fragments was developed and introduced in TRiP98. For the biological effect calculations the last version of the local effect model was used. The model predictions were experimentally verified at the HIT facility. The primary beam attenuation and the characteristics of secondary charged particles at various depth in water were investigated using He-4 ion beams of 200 MeV/u. The nuclear charge of secondary fragments was identified using a Delta E/E telescope. 3D absorbed dose distributions were measured with pin point ionization chambers and the biological dosimetry experiments were realized irradiating a Chinese hamster ovary cells stack arranged in an extended target. Results: The few experimental data available on basic physical processes are reproduced by their beam model. The experimental verification of absorbed dose distributions in extended target volumes yields an overall agreement, with a slight underestimation of the lateral spread. Cell survival along a 4 cm extended target is reproduced with remarkable accuracy. Conclusions: The authors presented a simple simulation model for therapeutical He-4 beams which they introduced in TRiP98, and which is validated experimentally by means of physical and biological dosimetries. Thus, it is now possible to perform detailed treatment planning studies with He-4 beams, either exclusively or in combination with other ion modalities. (C) 2016 Author(s)

Galactic Core-Collapse Supernovae at IceCube: “Fire Drill” Data Challenges and follow-up

The next Galactic core-collapse supernova (CCSN) presents a once-in-a-lifetime opportunity to make astrophysical measurements using neutrinos, gravitational waves, and electromagnetic radiation. CCSNe local to the Milky Way are extremely rare, so it is paramount that detectors are prepared to observe the signal when it arrives. The IceCube Neutrino Observatory, a gigaton water Cherenkov detector below the South Pole, is sensitive to the burst of neutrinos released by a Galactic CCSN at a level >10σ. This burst of neutrinos precedes optical emission by hours to days, enabling neutrinos to serve as an early warning for follow-up observation. IceCube\u27s detection capabilities make it a cornerstone of the global network of neutrino detectors monitoring for Galactic CCSNe, the SuperNova Early Warning System (SNEWS 2.0). In this contribution, we describe IceCube\u27s sensitivity to Galactic CCSNe and strategies for operational readiness, including "fire drill" data challenges. We also discuss coordination with SNEWS 2.0

All-Energy Search for Solar Atmospheric Neutrinos with IceCube

The interaction of cosmic rays with the solar atmosphere generates a secondary flux of mesons that decay into photons and neutrinos – the so-called solar atmospheric flux. Although the gamma-ray component of this flux has been observed in Fermi-LAT and HAWC Observatory data, the neutrino component remains undetected. The energy distribution of those neutrinos follows a soft spectrum that extends from the GeV to the multi-TeV range, making large Cherenkov neutrino telescopes a suitable for probing this flux. In this contribution, we will discuss current progress of a search for the solar neutrino flux by the IceCube Neutrino Observatory using all available data since 2011. Compared to the previous analysis which considered only high-energy muon neutrino tracks, we will additionally consider events produced by all flavors of neutrinos down to GeV-scale energies. These new events should improve our analysis sensitivity since the flux falls quickly with energy. Determining the magnitude of the neutrino flux is essential, since it is an irreducible background to indirect solar dark matter searches