Hekla cold springs (Iceland): groundwater mixing with magmatic gases

We have analysed the chemical and stable isotope compositions of four spring waters situated just northwest of the Hekla volcano, where cold water emerges from the base of the lava flows. The stable isotope ratios of water (H, O), dissolved inorganic carbon (C) and sulphate (S) were used to determine whether magmatic gases are mixing with the groundwater. The waters can be characterised as Na-HCO₃ type. The results show that deep-seated gases mix with groundwater, substantially affecting the concentration of solutes and the isotopic composition of dissolved carbon and sulphate.     

Electron-impact induced fluorescence for EUV spectrometer–detector calibration

EUV-Spectra of electron-impact induced fluorescence from rare gases were recorded for an impact energy of 3.5 keV intending their application in the first step for spectrometer wavelength scale calibrations. The spectra are in the investigated range of 165–314 nm in good agreement with previously measured and calculated spectra. Nearly all observed lines could be identified including 196 new lines. 183 lines mainly for krypton and xenon could not be identified. The spectra are presented and discussed. A compendium of 1670 lines and their identification is added as supplementary tables. The spectra show a number of strong lines which are well suited for spectrometer wavelength scale calibrations and once their intensity relation is deduced can be used for a sensitivity determination of a spectrometer–detector combination as described in the introductory and experimental sections of the paper.     

On Rayleight instability in decaying plane Couette flow

The inflexion point criterion of Rayleigh is one of the most well-known results in hydrodynamic stability theory but cannot easily be demonstrated experimentally in wall bounded flows. For plane Couette flow, where both walls move with equal speed in opposite directions, it is possible to establish a (time-dependent) inflectional velocity profile if both walls are brought momentarily to rest. If the Reynolds number is high enough a growing stationary instability develops. This situation is ideally suited for flow visualization of the instability. In this paper we show flow visualization experiments and stability calculations of the developing transverse roll cell instability in such a flow at low Reynolds numbers. Although the stability calculations are based on a quasi-stationary velocity profile, the measured and most amplified wave length obtained from the calculations are in excellent agreement.     

Behavior of captive herring exposed to naval sonar transmissions (1.0-1.6 kHz) throughout a yearly cycle

Atlantic herring, Clupea harengus, is a hearing specialist, and several studies have demonstrated strong responses to man-made noise, for example, from an approaching vessel. To avoid negative impacts from naval sonar operations, a set of studies of reaction patters of herring to low-frequency (1.0-1.5 kHz) naval sonar signals has been undertaken. This paper presents herring reactions to sonar signals and other stimuli when kept in captivity under detailed acoustic and video monitoring. Throughout the experiment, spanning three seasons of a year, the fish did not react significantly to sonar signals from a passing frigate, at received root-mean-square sound-pressure level (SPL) up to 168 dB re 1 μPa. In contrast, the fish did exhibit a significant diving reaction when exposed to other sounds, with a much lower SPL, e.g., from a two-stroke engine. This shows that the experimental setup is sensitive to herring reactions when occurring. The lack of herring reaction to sonar signals is consistent with earlier in situ behavioral studies. The complexity of the behavioral reactions in captivity underline the need for better understanding of the causal relationship between stimuli and reaction patterns of fish.     

Nano‐antennae assisted emission of extreme ultraviolet radiation

High‐order harmonic generation in xenon with oscillator repetition rates is studied. The necessary intensity is reached via plasmonic field enhancement at nanostructured arrays of bow‐tie gold antennae. The theoretical analysis focuses on the thermal properties and the damage threshold of the bow‐tie antennae. On the experimental side the number of contributing atoms is determined and optimized. Extreme ultraviolet radiation is successfully observed with photon fluxes almost an order of magnitude larger than previously reported.