How fast does tufa grow? Very high-resolution measurement of the tufa growth rate on artificial substrates by the development of a contactless image-based modelling device

Accurate determination of the tufa growth rate (TGR) is required to answer the fundamental geomorphological question of tufa evolution. The TGR has been measured by various direct and indirect methods. One of the most popular direct methods uses modified micro-erosion meter (MEM), which has several drawbacks. Here, we present for the first time a coordinate measuring macro-photogrammetry device (CMD) for monitoring the TGR in a contactless manner. The CMD was applied on 28 limestone plates at 14 locations within the Skradinski buk area, Croatia, and measurements were performed in the laboratory. The TGR was derived from digital tufa high-resolution models (DTHRMs). The accuracy of the device was evaluated using state-of-the-art three-dimensional (3D) scanners and error calculation at checkpoints. Moreover, the precision was evaluated with the split test (n = 5). A total of 74 DTHRMs with a spatial resolution of 0.0236 mm were created. The TGR ranged from 0.327 to 19.302 mm a⁻¹, with an average of 5.771 mm a⁻¹. A higher TGR was observed on the limestone plates near mosses, located in fast and turbulent water rather than in stagnant water. We found that specific micro-environmental factors (e.g. proximity to moss) positively affected tufa growth. Erosion events were observed, as well as the presence of aquatic insect larvae (Simuliidae and Chironomidae), which positively affected tufa growth. The CMD is a precise and accurate device that does not suffer from the drawbacks of the MEM method and has many other advantages. It has a high capability of tufa erosion detection, enables the identification of macroinvertebrates, and multispectral or hyperspectral cameras can be mounted on the device for spectral reflectance analysis of the tufa surface. The CMD can be applied in any study requiring a sub-millimetre data quality and involving the comparison of consecutive 3D models and derivation of various parameters of smaller objects. © 2020 John Wiley & Sons, Ltd.     

The Equal Earth map projection

The Equal Earth map projection is a new equal-area pseudocylindrical projection for world maps. It is inspired by the widely used Robinson projection, but unlike the Robinson projection, retains the relative size of areas. The projection equations are simple to implement and fast to evaluate. Continental outlines are shown in a visually pleasing and balanced way.     

Surface current patterns in front of the Venice Lagoon

Surface patterns of the low-frequency current in a 20 × 30 km region in front of the Venice Lagoon were analysed from a 13-month-long HF radar data set. Surface circulation was related to prevalent wind regimes in the area and to the tidal flow through the lagoon inlet. Three different categories of wind-forcing were defined: bora (NE wind), sirocco (SE wind), and finally the category containing all other wind directions and calms (winds lower than 3 m/sec). Mean flow and vorticity spatial distributions were discussed for different wind conditions. The coastal area about 5 km wide is characterized by a flow field with maximum vorticity. Outside the coastal boundary layer the interior flow is part of the Adriatic basin-wide cyclonic circulation. Two counter-rotating vortices of the dimension of about 4–5 km were evidenced in the average flow field in front of the lagoon inlet (Malamocco inlet) in all situations except for the bora. The vortex-pair is probably associated with the tidal flow through the inlet. The bora wind induces a strong southward coastal jet detached from the coast by about 5 km homogenizing the flow and eliminating the dipole. The average coastal flow pattern in calm wind conditions was also analysed as a function of the strong inflow/outflow (currents in the inlet > 0.7 m s⁻¹) from the lagoon inlet. In both cases the vorticity pattern is similar, with the negative vorticity to the left of the inlet and positive to the right looking seaward.     

An Outburst Detected in the Spectrum of Hd 6226

HD 6226 is a bright binary Be star at visual magnitude 6.81 (Hipparcos database). The emission and absorption phases occur in cycles, which are probably not periodic. The suspected period of about 630 days (derived from photometric measurements) is not confirmed by our spectroscopic survey. The latest emission phase developed in the beginning of 2003, then the emission strength systematically decreased and disappeared between July 21, 2003 and August 4, 2003. The last (absorption) spectrum was exposed on August 25, 2003. Unexpected very strong emission appeared in a spectrum exposed on October 28, 2003. A short-term photometric brightening followed this “outburst”. Long-term spectroscopic RV studies revealed a 2.615 d period modulated by a 29.7 d period (in the He I 6678 line), which perhaps may be interpreted as orbital period of a binary. Nevertheless, the physical nature of the dominant short 2.615 d period is not yet clear. The last detected emission episode has changed considerably our view of the interesting object HD 6226. We hope this study will reveal more details of the physical properties of the Be phenomenon.     

A hypothetical end of creative-expansive evolution phase of the expansive non-decelerative universe

The hypothetical final parameters of the Universe result from the model properties of the expansive non-decelerative universe and properties of the hypothetical primordial black holes.     

A measure of inhomogeneity of the expansive nondecelerative universe

The measure of inhomogeneity of the expansive nondecelerative Universe is obtained.     

Transient brightenings of interconnecting loops

We discuss three different kinds of dynamic events related to interconnecting loops observed in soft X-rays aboard Skylab: (1) A newly born transequatorial loop that was either emerging from subphotospheric layers or gradually filled in with hot plasma. (2) Large-scale twists of interconnecting loops which never relax, and often only form, after the loop brightenings. (3) Three events where the loop that later interconnected two active regions had been visible long before one of the interconnecting regions was born. Several impacts this observation might have upon our understanding of the process of flux emergence are suggested.     

Intrinsic polarization changes and the Hα and Caii emission features in T-Tauri stars

On grounds of the correlation between polarization and emission features observed in some T-Tauri stars, it is concluded that flaring effects associated with UV and/or X-ray irradiation and with increased magnetic field are the cause of the intrinsic polarization changes in T-Tauri stars.     

Free-free opacity in strong magnetic fields

A way of computing the absorption cross-section for photons on electrons undergoing free-free transitions in magnetic plasma is described. Theoretical expressions for the free-free cross sections in magnetic plasma are given in a representation in which they can be easily compared with the classical results in the absence of the magnetic field. The results of numerical computations of these cross-sections are also presented and discussed. Finally the free-free cross-sections are averaged over the electron states in magnetic plasma in thermal equilibrium, yielding the opacity coefficient as a function of photons frequency. The results of numerical computations are given in graphical form.