Anatomical description of Pisidium johnsoni EA Smith, 1882 (Bivalvia : Sphaeriidae) from Madagascar

Volume: 45Start Page: 358End Page: 36

Synthesis of controllers for electromechanical tracking systems

The article presents an algorithm for the synthesis of regulators for servomechanisms, in which the control object is linear. The algorithm is focused on electromechanical systems, the main element of which is a controlled electric drive. The synthesis algorithm is based on the use of the L–Markov moment problem. The advantage of the proposed algorithm with respect to the others is that the regulators synthesized on its basis ensure the minimization of energy for the objects control. The essence of the proposed algorithm of synthesis is that the control, according to the provisions underlying the L – moment problem, can be determined not only through the system of moment functions, but also through the moments. The latter depends both on the time interval during which the object is transferred from the initial state to the final state, but also on the state of the object itself. To solve the problem of controller design for servo systems, the following is proposed: 1. Explicitly express management through moments. 2. Perform «unfreezing» the initial and final states of the object. When «unfreezing» the initial state of the object is considered to be the current phase, and the final state is determined by the monitored signal. The time interval during which the object is transferred from one state to another is set arbitrarily in the general case. However, the longer this interval, the smaller the control rate, but, respectively, the greater the tracking error

Moitessier\u27s pea clam Pisidium moitessierianum (Bivalvia, Sphaeriidae): A cryptogenic mollusc in the Great Lakes

Pisidium moitessierianum Paladilhe, 1866, a small pea clam native to Europe, was identified for the first time from the lower Great Lakes basin based on an examination of historical collections of Pisidium performed by V. Sterki in 1894 and 1903 and new material collected during 1997 and 1998. During recent surveys, P. moitessierianum individuals were found in the St. Clair River delta, Lake St. Clair and western Lake Erie, but were not detected in the Detroit River or western Lake Ontario. Pisidium moitessierianum was collected on sand, silty sand and mud substrata from water depths ranging between 0.6 and 5.4 m. Populations occurred at an average density of 51 ind. m-2 and included juveniles and adults. All individuals were less than 2.0 mm in length. We examined the structure of the umbos and hinge, surface sculpture and shape of the shell, and the anatomy of gills, mantle and nephridia in populations from the lower Great Lakes and Ukrainian inland basins (Dnieper River and Lake Beloye). The results indicated that the Great Lakes\u27 pea clams match European specimens of P. moitessierianum in these conchological and anatomical characteristics. As with other nonindigenous sphaeriids in the Great Lakes, P. moitessierianum was likely introduced through shipping activities into the Great Lakes, possibly as early as the 1890s

SYNTHESIS OF OPTIMAL CONTROLS FOR NONLINEAR OBJECTS BY THE CRITERION OF MAXIMUM SPEED

The  article  presents  an  algorithm  for  synthesizing  optimal  program  controls  for  nonlinear  control-affine  objects  by  the criterion  of  maximum  speedy.  The  mathematical  apparatus  used  is  the  linearization  of  Newton-Kantorovich  and  the apparatus of matrix operators. The structure of the algorithm includes the following steps at the first stage, the linearization of the nonlinear mathematical model of the object is performed by the Newton-Kantorovich method; at the second stage, we carry out the reduction of the synthesis problem by the criterion of minimum time in the presence of constraints on the control energy to the synthesis problem by the energy minimum criterion for finding the (optimal) minimum value of the sought  time;  at  the  third  stage  we  perform  parametrization  of  the  mathematical  model  of  the  control  object  and  a  new quality criterion using the apparatus of matrix operators with the subsequent construction of the optimal control. The fourth final  stage  consists  in  realizing  the  iterative  process  prescribed  by  the  Newton-Kantorovich  method-there  is  an  optimal (minimal) time value. The synthesis algorithm is illustrated by an example

Lake Superior: An invasion coldspot?

Lake Superior receives a disproportionate number of ballast water discharges from transoceanic ships operating on the Laurentian Great Lakes. Although this provides dispersal opportunities for nonindigenous species (NIS), relatively few NIS were initially discovered in this lake prior to being recorded elsewhere in the basin. A lack of NIS records from this lake may be an artefact of sampling bias. We tested this hypothesis by sampling benthos and plankton from littoral and deepwater habitats around the perimeter of Lake Superior during June and August 2001. Using morphological analysis techniques, we identified a total of 230 invertebrate taxa representing planktonic, benthic and nektonic lifestyles. Five species with invasion histories in the lower Great Lakes, the bivalves Sphaerium corneum, Pisidium amnicum and P. moitessierianum, gastropod Potamopyrgus antipodarum and amphipod Echinogammarus ischnus, were identified for the first time in Lake Superior. In addition, records of expanded distributions within this lake are presented for the amphipod Gammarus fasciatus and oligochaetes Ripistes parasita and Vejdovskyella intermedia. Recently introduced NIS in Lake Superior were found near international ports, implicating shipping as the vector of their introduction. Intrinsic physical-chemical aspects of Lake Superior may account for the scarcity of NIS in this lake as compared to the lower Great Lakes