P. Erdős asked how frequently does 2n have a ternary expansion that omits the digit 2. He conjectured that this holds only for finitely many values of n. We generalize this question to consider iterates of two discrete dynamical systems. The first considers truncated ternary expansions of real sequences xn(λ) = ⌊λ2n⌋, where λ > 0 is a real number, along with its untruncated version, while the s...

P. Erdős asked how frequently the ternary expansion of 2 omits the digit 2. He conjectured this holds only for finitely many values of n. We generalize this question to iterates of two discrete dynamical systems. We consider real sequences xn(λ) = ⌊λ2 ⌋, where λ > 0 is a real number, and 3-adic integer sequences yn(λ) = λ2 , where λ is a 3-adic integer. We show that the set of initial values ha...

P. Erdős asked how frequently 2 has a ternary expansion that omits the digit 2. He conjectured this holds only for finitely many values of n. We generalize this question to consider iterates of two discrete dynamical systems. The first considers ternary expansions of real sequences xn(λ) = ⌊λ2 ⌋, where λ > 0 is a real number, and the second considers 3-adic expansions of sequences yn(λ) = λ2 , ...

Symbolic substitution, a parallel processing technique, has been proposed in computing literature to perform fast, carry-free addition of numbers. Several algorithms and corresponding symbolic substitution tables have been developed for addition of two numbers represented in binary, modified signed digit (MSD), and canonical modified signed digit (CMSD) number systems. In this paper, however, w...

Air traffic controllers simultaneously develop complex and multiple tasks in the course of their activities. In this context, concern is raised over the high level of attention needed by these professionals which can ultimately be affected by stress and fatigue. Objectives The objective of this study was to assess attention level in air traffic controllers (ATCo). Methods 45 flight protecti...

We report an investigation of postural stability in two groups of volunteers (mean ages of 57 and 77). Participants were required to stand on a force platform while performing five cognitive tasks: (1) random digit generation, (2) Brooks' spatial memory, (3) backward digit recall, (4) silently counting from 1-100, and (5) counting backward in threes (aloud). There was also a control condition i...

P. Erdős asked how frequently 2 has a ternary expansion that omits the digit 2. He conjectured this holds only for finitely many values of n. We generalize this question to consider iterates of two discrete dynamical systems. The first considers ternary expansions of real sequences xn(λ) = ⌊λ2 ⌋, where λ > 0 is a real number, and the second considers 3-adic expansions of sequences yn(λ) = λ2 , ...

Young and older adults were administered digit and location memory span tasks with and without verbal and spatial secondary tasks. Age differences were greater in location span than in digit span; however, there were no age differences in either the magnitude or pattern of effects of secondary tasks. There were also no age differences in the effects of secondary tasks on a combined (digit and l...