Bimodal rheotactic behavior reflects flagellar beat asymmetry in human sperm cells

Successful sperm navigation is essential for sexual reproduction, yet we still understand relatively little about how sperm cells are able to adapt their swimming motion in response to chemical and physical cues. This lack of knowledge is owed to the fact that it has been difficult to observe directly the full 3D dynamics of the whip-like flagellum that propels the cell through the fluid. To overcome this deficiency, we apply a new algorithm to reconstruct the 3D beat patterns of human sperm cells in experiments under varying flow conditions. Our analysis reveals that the swimming strokes of human sperm are considerably more complex than previously thought, and that sperm may use their heads as rudders to turn right or left.Swiss National Science Foundation (Grant 148743)Solomon Buchsbaum AT&T Research Fun

FEATURES OF MEASURING IN LIQUID MEDIA BY ATOMIC FORCE MICROSCOPY

Subject of Research.The paper presents results of experimental study of measurement features in liquids by atomic force microscope to identify the best modes and buffered media as well as to find possible image artifacts and ways of their elimination. Method. The atomic force microscope Ntegra Aura (NT-MDT, Russia) with standard prism probe holder and liquid cell was used to carry out measurements in liquids. The calibration lattice TGQ1 (NT-MDT, Russia) was chosen as investigated structure with a fixed shape and height. Main Results. The research of probe functioning in specific pH liquids (distilled water, PBS - sodium phosphate buffer, Na2HPO4 - borate buffer, NaOH 0.1 M, NaOH 0.5 M) was carried out in contact and semi-contact modes. The optimal operating conditions and the best media for the liquid measurements were found. Comparison of atomic force microscopy data with the results of lattice study by scanning electron microscopy was performed. The features of the feedback system response in the «probe-surface» interaction were considered by the approach/retraction curves in the different environments. An artifact of image inversion was analyzed and recommendation for its elimination was provided. Practical Relevance. These studies reveal the possibility of fine alignment of research method for objects of organic and inorganic nature by atomic force microscopy in liquid media

LANGUAGE AGGRESSION ON THE INTERNET - CALL MORAL IMPERATIVES

Virtual communication plays increasingly important role in daily life. As long as the Internet develops, it shapes out its own rules, customs and norms of interaction. For millions of people social networks became a socio-cultural environment, where they perceive social values and standards. However, these standards, unfortunately, are not always correlate with moral and legal norms. Among all kinds of Internet resources, networks placing defamatory, false or hostile information towards other individuals or groups (so called intolerant online communities) have been widely spread. The researchers most commonly associate deviant or aggressive behavior of Internet users with social networks. In this articlewe consider electronic verbal aggression towards users or groups of users of the Internet

Cell size sets the diameter of the budding yeast contractile ring.

The formation and maintenance of subcellular structures and organelles with a well-defined size is a key requirement for cell function, yet our understanding of the underlying size control mechanisms is limited. While budding yeast cell polarization and subsequent assembly of a septin ring at the site of bud formation has been successfully used as a model for biological self-assembly processes, the mechanisms that set the size of the septin ring at the bud neck are unknown. Here, we use live-cell imaging and genetic manipulation of cell volume to show that the septin ring diameter increases with cell volume. This cell-volume-dependence largely accounts for modulations of ring size due to changes in ploidy and genetic manipulation of cell polarization. Our findings suggest that the ring diameter is set through the dynamic interplay of septin recruitment and Cdc42 polarization, establishing it as a model for size homeostasis of self-assembling organelles. Budding yeast cell polarization is known to self-assemble, but it is still not clear what controls the size of the resulting septin ring. Here the authors show that the septin ring diameter is set by cell volume, ensuring that larger cells have larger rings

An asymmetric flow-focusing droplet generator promotes rapid mixing of reagents.

Nowadays droplet microfluidics is widely used to perform high throughput assays and for the synthesis of micro- and nanoparticles. These applications usually require packaging several reagents into droplets and their mixing to start a biochemical reaction. For rapid mixing microfluidic devices usually require additional functional elements that make their designs more complex. Here we perform a series of 2D numerical simulations, followed by experimental studies, and introduce a novel asymmetric flow-focusing droplet generator, which enhances mixing during droplet formation due to a 2D or 3D asymmetric vortex, located in the droplet formation area of the microfluidic device. Our results suggest that 2D numerical simulations can be used for qualitative analysis of two-phase flows and droplet generation process in quasi-two-dimensional devices, while the relative simplicity of such simulations allows them to be easily applied to fairly complicated microfluidic geometries. Mixing inside droplets formed in the asymmetric generator occurs up to six times faster than in a conventional symmetric one. The best mixing efficiency is achieved in a specific range of droplet volumes, which can be changed by scaling the geometry of the device. Thus, the droplet generator suggested here can significantly simplify designs of microfluidic devices because it enables both the droplet formation and fast mixing of the reagents within droplets. Moreover, it can be used to precisely estimate reaction kinetics