Investigating variation of latitudinal stellar spot rotation and its relation to the real stellar surface rotation

In this work the latitude dependent stellar spot rotation is investigated based on dynamo models. The maps of the magnetic pressure at the surface from the dynamo calculations are treated similarly to the temperature maps obtained using Doppler imaging techniques. A series of snapshots from the dynamo models are cross-correlated to obtain the shift of the magnetic patterns at each latitude and time point. The surface differential rotation patterns obtained from the snapshots of the dynamo calculations show in all studied cases variability over the activity cycle. In the models using only the large scale dynamo field the measured rotation patterns are only at times similar to the input rotation law. This is due to the spot motion being mainly determined by the geometric properties of the large scale dynamo field. In the models with additional small scale magnetic field the surface differential rotation measured from the model follows well the input rotation law. The results imply that the stellar spots caused by the large scale dynamo field are not necessarily tracing the stellar differential rotation, whereas the spots formed from small scale fields trace well the surface flow patterns. It can be questioned whether the large spots observed in active stars could be caused by small scale fields. Therefore, it is not clear that the true stellar surface rotation can be recovered using measurements of large starspots, which are currently the only ones that can be observed.Comment: 8 pages, 10 figures, accepted for publication in A&

The first close-up of the "flip-flop" phenomenon in a single star

We present temperature maps of the active late-type giant FK Com which exhibit the first imagining record of the ``flip-flop'' phenomenon in a single star. The phenomenon, in which the main part of the spot activity shifts 180 degrees in longitude, discovered a decade ago in FK Com, was reported later also in a number of RS CVn binaries and a single young dwarf. With the surface images obtained right before and after the ``flip-flop'', we clearly show that the ``flip-flop'' phenomenon in FK Com is caused by changing the relative strengths of the spot groups at the two active longitudes, with no actual spot movements across the stellar surface, i.e. exactly as it happens in other active stars.Comment: 4 pages, accepted by A&A Letter

Fast Monotone Summation over Disjoint Sets

We study the problem of computing an ensemble of multiple sums where the summands in each sum are indexed by subsets of size $p$ of an $n$-element ground set. More precisely, the task is to compute, for each subset of size $q$ of the ground set, the sum over the values of all subsets of size $p$ that are disjoint from the subset of size $q$. We present an arithmetic circuit that, without subtraction, solves the problem using $O((n^p+n^q)\log n)$ arithmetic gates, all monotone; for constant $p$, $q$ this is within the factor $\log n$ of the optimal. The circuit design is based on viewing the summation as a "set nucleation" task and using a tree-projection approach to implement the nucleation. Applications include improved algorithms for counting heaviest $k$-paths in a weighted graph, computing permanents of rectangular matrices, and dynamic feature selection in machine learning

Effects of Digging Substrate on Growth and Fur in Blue Versus Shadow Type of Alopex Lagopus

. Our study sought to establish the extent to which digging substrate in the cage affects growth performance and fur properties in farmed foxes (Alopex lagopus) of the shadow white and blue colour types. The plates were on either the wall or the floor; the sandbox was always on the floor. A standard cage without any digging substrate was used as a control. There were 20 foxes in each group (one male and one female per cage). The cage setups were as follows: 1) a standard cage (105 cm long × 115 cm wide × 70 cm high) without digging substrates, which housed the control group; 2) a standard cage (105 cm long × 115 cm wide × 70 cm high) with a solid metal plate (210 × 297 mm) on the wall for digging and scratching; 3) a standard cage (105 cm long × 115 cm wide × 70 cm high) with a solid metal plate (210 × 297 mm) on the floor for digging and scratching; and 4) a standard cage (105 cm long × 115 cm wide × 70 cm high) with a metal sandbox for digging and scratching (80 × 40 × 14 cm, L×W×H). The sandbox had a 10 cm layer of sand (ca. 25 kg, particle size 0-18 mm) on the bottom. All animals grew well and reached normal body weights. No significant growth differences were found between blue and shadow types within the groups. Furthermore, skin length did not differ between colour types or between groups. Skin weight, on the other hand, was heavier in the blue than in the shadow type in the plate floor groups. No differences were recorded in the other groups. Fur quality was poorest in the blue type of the standard group and best in the shadow type of the plate wall group. Cover and mass were also best in the shadow type of the plate wall group. Furs were dirtiest in the sandbox groups, irrespective of colour type. Our findings tempt us to conclude that body growth is highly affected by digging substrate and that a sandbox in the cage causes the dirtiest fur and may, therefore, be avoided in farming practice

Ternary nucleation of H_2SO_4, NH_3 and H_2O

A classical theory of the ternary homogeneous nucleation of sulfuric acid—ammonia—water is presented. For NH3 mixing ratios exceeding 1 ppt, the presence of ammonia enhances the binary (sulfuric acid—water) nucleation rate by several orders of magnitude. However, the limiting component for ternary nucleation—as for binary nucleation—is sulfuric acid. The sulfuric acid concentration needed for significant ternary nucleation is several orders of magnitude below that required in binary case