Structural dynamics of a helicopter rotor blade system

An experimental and analytical study was conducted to better understand the structural dynamic behavior of a rotor system subjected to inertial and structural loads without any aerodynamic loads. Vibration characteristics of a 6.32 ft diameter torsionally soft two-bladed rotor were measured in vacuum over a speed range of 0 to 1000 rpm and were compared with theoretical predictions from a fully nonlinear finite element model. Measurements of vibratory strains for five modes of vibration were made on the blades for several combinations of precone, droop, and flexure stiffness. Excellent agreement (within 0.5 percent) was found for all flapping and lead-lag modal frequencies

Effect of predation risk on the presence and persistence of yellow-bellied marmot (Marmota flaviventris) colonies

Habitat selection may have population level consequences and ultimately may influence a population's local persistence or extinction. We capitalized on a long-term study (1962-2004) of yellow-bellied marmots Marmota flaviventris in and around the Rocky Mountain Biological Laboratory, Gothic, Colorado, USA, and compared habitat characteristics associated with food availability and predation risk to explain variation in persistence of marmots at 27 sites, and their absence at 22 additional, randomly selected sites. We classified sites as persistent, intermittent or null based on whether there was a history of extinction; intermittent sites periodically went extinct and null sites never had marmots. Logistic regression analyses revealed that environmental variables associated with visibility and safety, rather than food, correctly classified sites as persistent or non-persistent as well as persistent or intermittent. Discriminant function analysis that included the null sites revealed that the same visibility-related characteristics predicted where marmots were found. These results highlight the importance of variation in safety among sites in predicting long-term population persistence, as well as a species' distribution

The Permian nonmarine bivalve Palaeanodonta Amalitzky, 1895: Position in the modern Bivalvia system

© 2015, Pleiades Publishing, Ltd. Bivalves assigned to the genus Palaeanodonta Amalitzky, 1895 comprise more than 30 species and are widespread in malacofaunas of the Permian Period in both Eurasia and Gondwana. The history of the establishment of Palaeanodonta, changes in the opinion of the author of the genus concerning its composition and type species are considered. Relationships of Palaeanodonta with the genus Naiadites Dawson, 1860, which was initially regarded as its senior synonym, and with Anthraconaia Trueman et Weir, 1946, which shows superficial similarity, are analyzed. Certain characters, such as the external opisthodetic ligament, reduced pseudotaxodont hinge, crossed lamellar comarginal and radial shell microstructure, resulted in the conclusion that the type species of the genus, Unio castor Eichwald, 1860, the species close to it, i.e., P. longissima (Netschajew) and P. rhomboidea (Netschajew), and also the species included in the group Palaeanodonta fischeri (Amal.) (P. subcastor (Amal.), P. okensis (Amal.), P. parallela (Amal.), P. obunca (Netschajew), P. amalitzkyi (Silantiev)), as well as the group Palaeanodonta dubia (Amal.) (P. umbonata (Amal.), P. sibirzevi (Amal.), P. indeterminata (Amal.), P. monstrum (Amal.)) belong to the genus Palaeomutela Amalitzky, 1892. The species listed are similar in the reduced pseudotaxodont hinge apparatus, which is characterized by a narrow hinge area and few small teeth, which are usually at most ten in number, and occasionally fewer down to complete disappearance. This character is the basis for the recognition of the subgenus Palaeanodonta Amalitzky, 1895 within the genus Palaeomutela Amalitzky, 1892. The diagnoses of the genus, subgenera, and their species composition are provided