Isotopic partitioning by small mammals in the subnivium

In the Arctic, food limitation is one of the driving factors behind small mammal population fluctuations. Active throughout the year, voles and lemmings (arvicoline rodents) are central prey in arctic food webs. Snow cover, however, makes the estimation of their winter diet challenging. We analyzed the isotopic composition of ever-growing incisors from species of voles and lemmings in northern Finland trapped in the spring and autumn. We found that resources appear to be reasonably partitioned and largely congruent with phylogeny. Our results reveal that winter resource use can be inferred from the tooth isotopic composition of rodents sampled in the spring, when trapping can be conducted, and that resources appear to be partitioned via competition under the snow.Peer reviewe

Developing a mathematical model of the tooth profile angles of thread milling cutter with helical flutes

It is established that the lead and back angles of teeth, angle of helical flutes available require for correcting a thread profile of milling cutter teeth to machine a thread with an appropriate degree of accuracy.Based on the previously developed geometrical model an experiment is conducted to calculate the values of tooth profile angles of thread milling cutters with helical flutes at variation of five factors in the established factorial space. When planning the experiment the full central composite draft has been elaborated in the coded form for five factors at three levels taking into account the orthogonality and the impossibility to conduct repeatedly experiments in the chosen points.As the conducted researches have shown that a nature of dependence of the tooth profile angle values on design and geometrical parameters of thread milling cutter is nonlinear, the second degree of an approximating polynom is accepted. As a consequence, to assess all the coefficients of the polynom of the second degree the factors have been varied at three levels.Based on the method of planning the mathematical models are developed to calculate the tooth profile angles of thread milling cutter with helical flutes allowing to obtain the values of angles depending on a pitch of thread, a cutter diameter, a rake angle, an angle of lead of helical flutes, and a back angle. In terms of making manual calculations the obtained polynoms are cumbersome, however when using the model in CAD systems of thread milling cutters there is no need to simplify it. The represented mathematical models can be chosen as starting ones at calculation of profile angles when designing the thread milling cutters with helical flutes.Calculation of the profile angles of the thread milling cutter under study made according to polynoms obtained for all combinations of factors has shown that an error of calculated values in comparison with the values obtained using a geometrical model does not exceed 1.3% that makes 0 °24' and is no more than a tolerance for a half of tooth profile angle according to GOST 1336-77.</p

Manufacture of composite electrochemical materials from suspended electrolytes

New composite electrochemical materials on a metallic substrate synthesized from suspended electrolytes with additives of kaolin and bentonite powders of the nanosized fraction are studied. The limiting concentrations of the additives in the electrolyte that warrant the retention of the decorative and special properties of the microchromium coating are determined. © 2013 Pleiades Publishing, Ltd

Manufacture of composite electrochemical materials from suspended electrolytes

New composite electrochemical materials on a metallic substrate synthesized from suspended electrolytes with additives of kaolin and bentonite powders of the nanosized fraction are studied. The limiting concentrations of the additives in the electrolyte that warrant the retention of the decorative and special properties of the microchromium coating are determined. © 2013 Pleiades Publishing, Ltd