All posts by tmertzi

Αχ, πού’σαι, νιότη, που’δειχνες, πως θα γινόμουν άλλος.

Πάλι μεθυσμένος είσαι, δυόμισι η ώρα της νυχτός.
Κι αν τα γόνατα σου τρέμαν, “εκρατιόσουνα” στητός
μπρός στο κάθε τραπεζάκι. – Γεια σου Κωνσταντή βαρβάτε!
-Καλησπερούδια αφεντικά, πώς τα καλοπερνάτε;

Ένας σου’δινε ποτήρι κι άλλος σου’δινεν ελιά.
Έτσι πέρασες γραμμή της γειτονιάς τα καπηλιά.
Κι αν σε πείραζε κανένας –αχ, εκείνος ο Τριβέλας!
έκανες, πως δεν ένιωθες και πάντα εγλυκογέλας.

Χτες και σήμερα ίδια κι όμοια, χρόνια μπρός, χρόνια μετά…
Η ύπαρξή σου σε σκοτάδια όλο πηχτότερα βουτά.
Τάχα η θέλησή σου λίγη, τάχα ο πόνος σου μεγάλος;
Αχ, πού’σαι, νιότη, που’δειχνες, πως θα γινόμουν άλλος.

(του Βάρναλη)

Keeping it radioactive: This is how a molten salt nuclear reactor works

Radioactive elements produce heat as they decay. Nuclear plants draw power from this process, and typically stabilize the temperature with water. But during a power outage, H2O—which needs pumps to flow—can’t always prevent meltdowns. Molten salt reactors, which instead control heat with melted lithium and potassium fluorides, have a fail-safe: If the electricity dies, a plug will melt, causing the salts to seep down a safety drain and solidify around the uranium, preventing overheating. After a decades-long lull in development, countries from China to Denmark are building new molten salt reactors.

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Quantum electrodynamics and the proton size

Finding discrepancies between the predictions of fundamental theories and experimental observations is the main driver to develop physics further — the route to more advanced theories (‘new physics’) that fix the discrepancies. In that sense, quantum electrodynamics (QED) is currently seen as the most advanced fundamental theory, serving as the blueprint for any other quantum field theory. Progress is expected to come from ever more precise testing through comparison of theoretical predictions and experimental data. A good test compares values that can be both computed and measured with high accuracy. Some QED predictions excel in that respect, such as for the transition frequencies of atomic hydrogen and the gyromagnetic ratio of the electron.

https://i0.wp.com/media.springernature.com/relative-r300-703_m1050/springer-static/image/art%3A10.1038%2Fs41567-018-0166-0/MediaObjects/41567_2018_166_Figa_HTML.jpg?resize=446%2C241&ssl=1

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The Heidelberg compact electron beam ion traps

Electron beam ion traps (EBITs) are ideal tools for both production and study of highly charged ions (HCIs). In order to reduce their construction, maintenance, and operation costs, we have developed a novel, compact, room-temperature design, the Heidelberg Compact EBIT (HC-EBIT). Four already commissioned devices operate at the strongest fields (up to 0.86 T) reported for such EBITs using permanent magnets, run electron beam currents up to 80 mA, and energies up to 10 keV. They demonstrate HCI production, trapping, and extraction of pulsed Ar16+ bunches and continuous 100 pA ion beams of highly charged Xe up to charge state 29+, already with a 4 mA, 2 keV electron beam. Moreover, HC-EBITs offer large solid-angle ports and thus high photon count rates, e.g., in x-ray spectroscopy of dielectronic recombination in HCIs up to Fe24+, achieving an electron-energy resolving power of EE > 1500 at 5 keV. Besides traditional on-axis electron guns, we have also implemented a novel off-axis gun for laser, synchrotron, and free-electron laser applications, offering clear optical access along the trap axis. We report on its first operation at a synchrotron radiation facility demonstrating the resonant photoexcitation of highly charged oxygen.

 

Figure

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Probing Sizes and Shapes of Nobelium Isotopes by Laser Spectroscopy

Until recently, ground-state nuclear moments of the heaviest nuclei could only be inferred from nuclear spectroscopy, where model assumptions are required. Laser spectroscopy in combination with modern atomic structure calculations is now able to probe these moments directly, in a comprehensive and nuclear-model-independent way. Here we report on unique access to the differential mean-square charge radii of 252,253,254No, and therefore to changes in nuclear size and shape. State-of-the-art nuclear density functional calculations describe well the changes in nuclear charge radii in the region of the heavy actinides, indicating an appreciable central depression in the deformed proton density distribution in 252,254No isotopes. Finally, the hyperfine splitting of 253No was evaluated, enabling a complementary measure of its (quadrupole) deformation, as well as an insight into the neutron single-particle wave function via the nuclear spin and magnetic moment.

 

Figure 3

Read the full article on Phys. Rev. Lett

Revelations from the dissolved 226Ra-228Ra pair distribution in the South East Pacific Ocean

While it is confirmed that 226Ra is an interesting tracer of the water masses encountered along the GP16 US East Pacific Zonal Transect (EPZT) section cruise, 228Ra data coupled to the dissolved iron (Fe), cobalt (Co) and manganese (Mn) ones provide evidence that lateral transport of sediments from continental margins, including shelves and slopes, play an important role in open ocean trace elements and isotopes (TEI) budgets and biogeochemistry.

Indeed, elevated 228Ra activities were measured in the upper 200 m over the entire transect, a distance of 8500 km, as a result of sedimentary inputs from the continental shelf. In addition, a deep 228Ra plume was observed at ~1000–2500 m as far as 600 km away from the margin.

Linear dissolved Mn/228Ra relationship is observed both in shelf and offshore surface waters, suggesting that shelf sediments were likely the main source of dissolved Mn to the upper ocean. A linear dissolved Co/228Ra relationship was also observed in surface waters off Peru but no specific dissolved Co/228Ra trend was seen in shelf waters underlining the more complex behavior of Co in this area. Finally, the dissolved Fe/228Ra gradient suggests a rapid removal of Fe.

These results evidence again the important yet underappreciated role of continental slopes as sedimentary TEI sources to the deep ocean.

18 Sanial

 

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Machine Learning approaches on submarine volcanic systems

The morphology and the activity of a submarine caldera, Avyssos, at the northern part of Nisyros volcano in the South Aegean Sea (Greece), has been studied by means of remotely-operated underwater vehicle dives. The recorded time series of temperature and conductivity over the submarine volcano have been analyzed in terms of the generalized moments method. The findings of the mathematical analysis shed light on the volcanic activity, but also on the morphology (shape) of the submarine volcano. The conductivity time series indicates that the volcano is at rest, in agreement with other types of observations. On the other hand, temperature fluctuations, which in general describe a multifractal process, show that the submarine caldera operates as an open system that interacts with its surroundings. This type of analysis can be used as an indicator for the state of activity and the morphological structure (closed or open system) of a submarine volcano.

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Micro-bubble implosion, a reverse Big Bang

Laser pulse compression technology invented in the late 1980s resulted in high-power, short-pulse laser techniques, enhancing laser intensity 10 million-fold in a quarter of a century.

Scientists at Osaka University discovered a novel particle acceleration mechanism they describe as a micro-bubble implosion, in which super-high energy hydrogen ions (relativistic protons) are emitted at the moment when bubbles shrink to atomic size through the irradiation of hydrides with micron-sized spherical bubbles by ultraintense laser pulses. Their research results were published in Scientific Reports.

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