Randomization in individual choice behavior.

There is ample evidence that people cannot generate random series when instructed to do so. Rather, they produce sequences with too few symmetries and long runs and too many alternations among events. The authors propose a psychological theory to account for these findings, which assumes that subjects generate nonrandom sequences that locally represent theoretical random series subject to a constraint on their short-term memory. Closed-form expressions are then derived for the major statistics that have been used to test for deviations from randomness. Results from 3 experiments with 2 and 3 equiprobable alternatives support the model on both the individual and group levels. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Provision of step-level public goods: Effects of inequality in resources.

Twelve groups of 5 players each participated in a multiple-trial social dilemma game in which each player, i, receives a possibly different monetary endowment, ei, and then chooses independently and anonymously whether to contribute it to a monetary public good. The collective good, r, is supplied to all of the group members if the sum of contributions is equal to or larger than a prespecified and known threshold; it is not supplied otherwise. It was found (a) that the proportion of contributions decreased with experience, (b) that players contributed more often, the higher their endowment, but (c) that players with lower endowments were perceived to be more likely to contribute than were players with higher endowments. Group data provided strong support to a model in which the decision to contribute or not depends on ei and r, altruism, group size, and the probability of being critical to the group outcome. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Autoimmune diabetes induced by the beta-cell toxin STZ. Immunity to the 60-kDa heat shock protein and to insulin

Administered at a suitably low dose, the toxin streptozotocin (STZ) can trigger an autoimmune process leading to destruction of the beta-cells of the pancreatic islets. In this study, we examined specific immunological reactions in mice before and during the development of STZ-induced autoimmune diabetes. We now report that the development of spontaneous autoantibodies to insulin can serve as a marker of susceptibility to a low dose of STZ. Susceptible male mice of the C57BL/KsJ strain manifested such anti-insulin antibodies, and resistant female mice did not. Administration of a low dose of STZ (five daily doses each of 30 mg/kg) induced transient hyperglycemia approximately 20-30 days later, which temporarily remitted but was followed by intractable diabetes approximately 2.5 months later. The diabetogenic process triggered by the low dose of STZ was associated with an increase in the level of anti-insulin antibodies bearing the Dana and Micha (DM) idiotype, later followed by the appearance of anti-idiotypic antibodies that peaked before the onset of diabetes. Antibodies and T-cells reactive to hsp60 (heat shock protein) were triggered by the low-dose STZ administration and persisted throughout the period that preceded clinical diabetes. T-cells reactive to the p277 peptide of hsp60 were also observed. Finally, active immunization to hsp60 caused transient hyperglycemia by itself and also aggravated the hyperglycemia induced by low-dose STZ. Thus, autoantibodies to insulin can indicate susceptibility to a toxic trigger of diabetes, and a low dose of a toxin can activate the insulin and hsp60 autoimmunity that has been detected previously in the spontaneous autoimmune diabetes of NOD strain mice.     

Diverse Fab specific for acetylcholine receptor epitopes from a myasthenia gravis thymus combinatorial library

The muscle weakness in myasthenia gravis (MG) is caused by heterogeneous high-affinity IgG autoantibodies to the nicotinic acetylcholine receptor (AChR), a complex ion channel glycoprotein. These antibodies are clearly responsible for reducing AChR numbers at the neuromuscular junction in myasthenia; however, the origins, diversity, specificity and pathogenicity of individual antibodies have not yet been established. We have cloned and characterized four different AChR-specific Fab from an MG patient's thymus by screening an IgG1/kappa gene combinatorial lambda phage library with soluble human AChR labeled with [125I] alpha-bungarotoxin. Unlike most previously cloned human antibodies, all four Fab immunoprecipitated soluble human muscle AChR. Two Fab strongly inhibited binding of mAb to the main immunogenic region on the alpha subunits and one Fab bound to an epitope on the fetal-specific gamma subunit. In sensitivity and fine specificity, these Fab resembled the anti-AChR antibodies found in many MG patients, including the donor. The closest germline counterparts for their heavy chains were in VH families 1, 3 and 4; however, there were many differences consistent with an antigen-driven response of diverse B cell clones. The combinatorial approach holds promise for further analysis of human autoantibodies.     

The periodic solution of two-dimensional linear nonstationary systems and estimation of the attraction domain boundary in the problem of control of a wheeled robot

For the problem of control of the plane motion of a wheeled robot the estimate of the attraction domain is set up, which ensures the prescribed exponential speed of asymptotic stability and the absence of overcontrol. This statement of the problem is the generalization of the problems “on the attraction domain,” “on overcontrol,” and “on monotone damping,” which were stated by A.M. Letov in the work [1]. To define the attractive domain estimate, periodic trajectories are considered, which exist at the boundary of the stability domain of twodimensional linear nonstationary systems. Periodic solutions have a finite number of switchings over the period and describe the attraction domain boundary satisfying the preset geometric constraints.     

Motion control for a wheeled robot following a curvilinear path

A control synthesis problem for planar motion of a wheeled robot with regard to the steering gear dynamics is considered. The control goal is to bring the robot to a given curvilinear path and to stabilize its motion along the path. The trajectory is assumed to be an arbitrary parameterized smooth curve satisfying some additional curvature constraints. A change of variables is found by means of which the system of differential equations governing controlled motion of the robot reduces to the form that admits feedback linearization. A control law is synthesized for an arbitrary target path with regard to phase and control constraints. The form of the boundary manifold and the phase portrait of the system for the case of the straight target trajectory are studied. Results of numerical experiments are presented.     

Dislocation Structure and Stick–Slip Phenomenon

Friction is a complex process involving multi-scale asperity contact and large plastic deformation associated with the development of a dislocation structure. Friction is closely associated with the stick–slip phenomenon. In spite of the large number of papers, dedicated to stick–slip effects, little effort has been directed toward elucidating the development of the dislocation structure during stick–slip phenomena. Here, we report some new systematic investigations into the dislocation nature of stick–slips during low-velocity friction of a lithium fluoride single crystal rubbed against a spherical diamond indenter. It is shown that the average velocity of the indenter in the stick phase is about 300 times lower than the maximal velocity in the slip. This difference in velocities leads to entirely different dislocation behavior and damage development in the stick and slips phases. The stick phase is mainly determined by time-dependent strain (creep) wherein, as in metals and alloys, three stages of creep are observed. Based on the analysis of the dislocation structure, a model of the dislocation distribution in the regions of stick (creep) and slip is proposed.