3,062 research outputs found
A technique to investigate space maintenance tasks
Effects of space suit pressurization and weightlessness on performance decrement in space maintenance activit
Optimal self-assembly of finite shapes at temperature 1 in 3D
Working in a three-dimensional variant of Winfree's abstract Tile Assembly
Model, we show that, for an arbitrary finite, connected shape , there is a tile set that uniquely self-assembles into a 3D
representation of a scaled-up version of at temperature 1 in 3D with
optimal program-size complexity (the "program-size complexity", also known as
"tile complexity", of a shape is the minimum number of tile types required to
uniquely self-assemble it). Moreover, our construction is "just barely" 3D in
the sense that it only places tiles in the and planes. Our
result is essentially a just-barely 3D temperature 1 simulation of a similar 2D
temperature 2 result by Soloveichik and Winfree (SICOMP 2007)
The rate of leukocyte telomere shortening predicts mortality from cardiovascular disease in elderly men
Telomere length (TL) has been proposed as a marker of
mitotic cell age and as a general index of human organismic aging. Short
absolute leukocyte telomere length has been linked to
cardiovascular-related morbidity and mortality. Our aim was to test
whether the rate of change in leukocyte TL is related to mortality in a
healthy elderly cohort. We examined a subsample of 236 randomly selected
Caucasian participants from the MacArthur Health Aging Study (aged 70 to 79
years). DNA samples from baseline and 2.5 years later were assayed for
mean TL of leukocytes. Percent change in TL was calculated as a measure of
TL change (TLC). Associations between TL and TLC with 12-year overall and
cardiovascular mortality were assessed. Over the 2.5 year period, 46% of
the study participants showed maintenance of mean bulk TL, whereas 30%
showed telomere shortening, and, unexpectedly, 24% showed telomere
lengthening. For women, short baseline TL was related to greater mortality
from cardiovascular disease (OR = 2.3; 95% CI: 1.0 - 5.3). For men, TLC
(specifically shortening), but not baseline TL, was related to greater
cardiovascular mortality, OR = 3.0 (95% CI: 1.1 - 8.2). This is the first
demonstration that rate of telomere length change (TLC) predicts mortality
and thus may be a useful prognostic factor for longevity
Binary pattern tile set synthesis is NP-hard
In the field of algorithmic self-assembly, a long-standing unproven
conjecture has been that of the NP-hardness of binary pattern tile set
synthesis (2-PATS). The -PATS problem is that of designing a tile assembly
system with the smallest number of tile types which will self-assemble an input
pattern of colors. Of both theoretical and practical significance, -PATS
has been studied in a series of papers which have shown -PATS to be NP-hard
for , , and then . In this paper, we close the
fundamental conjecture that 2-PATS is NP-hard, concluding this line of study.
While most of our proof relies on standard mathematical proof techniques, one
crucial lemma makes use of a computer-assisted proof, which is a relatively
novel but increasingly utilized paradigm for deriving proofs for complex
mathematical problems. This tool is especially powerful for attacking
combinatorial problems, as exemplified by the proof of the four color theorem
by Appel and Haken (simplified later by Robertson, Sanders, Seymour, and
Thomas) or the recent important advance on the Erd\H{o}s discrepancy problem by
Konev and Lisitsa using computer programs. We utilize a massively parallel
algorithm and thus turn an otherwise intractable portion of our proof into a
program which requires approximately a year of computation time, bringing the
use of computer-assisted proofs to a new scale. We fully detail the algorithm
employed by our code, and make the code freely available online
Rate-equation calculations of the current flow through two-site molecular device and DNA-based junction
Here we present the calculations of incoherent current flowing through the
two-site molecular device as well as the DNA-based junction within the
rate-equation approach. Few interesting phenomena are discussed in detail.
Structural asymmetry of two-site molecule results in rectification effect,
which can be neutralized by asymmetric voltage drop at the molecule-metal
contacts due to coupling asymmetry. The results received for poly(dG)-poly(dC)
DNA molecule reveal the coupling- and temperature-independent saturation effect
of the current at high voltages, where for short chains we establish the
inverse square distance dependence. Besides, we document the shift of the
conductance peak in the direction to higher voltages due to the temperature
decrease.Comment: 12 pages, 6 figure
Successful ageing : perceptions of adults aged between 70 and 101 years
In this research, content analysis was employed to investigate older adults\u27 perceptions of successful aging and the relationship of these perceptions to definitions given in the literature to date. Participants were 18 males and 42 females between the ages of 70 and 101 years. Analyses revealed older adults mentioned only 1 or 2 criteria of successful aging if asked for a definition; however, when prompted, they rated almost all the criteria emerging from the literature as highly important. Participants reported adjusting to the situations they were in by compensating for losses that occurred and selecting activities that best suited their capabilities. Overall, older adults\u27 perceptions of successful aging were similar to aspects identified in the literature. Not all aspects, however, were seen as important by all participants, and only low to moderate correlations were found between some aspects of successful aging. (Contains 3 figures and 4 tables.)<br /
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