15,340 research outputs found
Approximate Self-Assembly of the Sierpinski Triangle
The Tile Assembly Model is a Turing universal model that Winfree introduced
in order to study the nanoscale self-assembly of complex (typically aperiodic)
DNA crystals. Winfree exhibited a self-assembly that tiles the first quadrant
of the Cartesian plane with specially labeled tiles appearing at exactly the
positions of points in the Sierpinski triangle. More recently, Lathrop, Lutz,
and Summers proved that the Sierpinski triangle cannot self-assemble in the
"strict" sense in which tiles are not allowed to appear at positions outside
the target structure. Here we investigate the strict self-assembly of sets that
approximate the Sierpinski triangle. We show that every set that does strictly
self-assemble disagrees with the Sierpinski triangle on a set with fractal
dimension at least that of the Sierpinski triangle (roughly 1.585), and that no
subset of the Sierpinski triangle with fractal dimension greater than 1
strictly self-assembles. We show that our bounds are tight, even when
restricted to supersets of the Sierpinski triangle, by presenting a strict
self-assembly that adds communication fibers to the fractal structure without
disturbing it. To verify this strict self-assembly we develop a generalization
of the local determinism method of Soloveichik and Winfree
Shuffle Invariance of the Super-RSK Algorithm
As in the -RSK (Robinson-Schensted-Knuth) of [1], other super-RSK
algorithms can be applied to sequences of variables from the set
, where , and . While
the -RSK of [1] is the case where for all and , these
other super-RSK's correspond to all the (\big{(}{{k+l}\atop{k}}\big{)}
shuffles of the 's and 's satisfying the above restrictions that
and . We show that the shape of the tableaux
produced by any such super-RSK is independent of the particular shuffle of the
's and 's.Comment: 22 page
Scaled tree fractals do not strictly self-assemble
In this paper, we show that any scaled-up version of any discrete
self-similar {\it tree} fractal does not strictly self-assemble, at any
temperature, in Winfree's abstract Tile Assembly Model.Comment: 13 pages, 3 figures, Appeared in the Proceedings of UCNC-2014, pp
27-39; Unconventional Computation and Natural Computation - 13th
International Conference, UCNC 2014, London, ON, Canada, July 14-18, 2014,
Springer Lecture Notes in Computer Science ISBN 978-3-319-08122-
Computational Extensive-Form Games
We define solution concepts appropriate for computationally bounded players
playing a fixed finite game. To do so, we need to define what it means for a
\emph{computational game}, which is a sequence of games that get larger in some
appropriate sense, to represent a single finite underlying extensive-form game.
Roughly speaking, we require all the games in the sequence to have essentially
the same structure as the underlying game, except that two histories that are
indistinguishable (i.e., in the same information set) in the underlying game
may correspond to histories that are only computationally indistinguishable in
the computational game. We define a computational version of both Nash
equilibrium and sequential equilibrium for computational games, and show that
every Nash (resp., sequential) equilibrium in the underlying game corresponds
to a computational Nash (resp., sequential) equilibrium in the computational
game. One advantage of our approach is that if a cryptographic protocol
represents an abstract game, then we can analyze its strategic behavior in the
abstract game, and thus separate the cryptographic analysis of the protocol
from the strategic analysis
Results of post-test psychological examinations of the crewmen from the 90-day manned test of an advanced regenerative life support system
The following material presents the results of two temporally remote administrations of an identical projective personality assessment device (Rorschach Inkblot) using crew members aboard the 90-day test. The first administration took place during preselection crew psychodiagnostic testing in the period extending from mid-December 1969 through mid-January 1970. Second administration took place in late May and early June, 1971, approximately one year after termination of the test. During the 90-day program duration, the subjects participated in the crew training program, were selected and served as onboard crew during the 90-day test. The testing was undertaken in order to determine the character and extent of change (if any) in basic personality dynamics accompanying or caused by participation in the 90-day test program. Results indicate that significant personality changes occurred in three of the four onboard crew members. A detailed discussion of the results is provided. Objective scores which served as the basis for the discussion are presented in the Appendix
Nanoscale Structure and Elasticity of Pillared DNA Nanotubes
We present an atomistic model of pillared DNA nanotubes (DNTs) and their
elastic properties which will facilitate further studies of these nanotubes in
several important nanotechnological and biological applications. In particular,
we introduce a computational design to create an atomistic model of a 6-helix
DNT (6HB) along with its two variants, 6HB flanked symmetrically by two double
helical DNA pillars (6HB+2) and 6HB flanked symmetrically by three double
helical DNA pillars (6HB+3). Analysis of 200 ns all-atom simulation
trajectories in the presence of explicit water and ions shows that these
structures are stable and well behaved in all three geometries. Hydrogen
bonding is well maintained for all variants of 6HB DNTs. We calculate the
persistence length of these nanotubes from their equilibrium bend angle
distributions. The values of persistence length are ~10 {\mu}m, which is 2
orders of magnitude larger than that of dsDNA. We also find a gradual increase
of persistence length with an increasing number of pillars, in quantitative
agreement with previous experimental findings. To have a quantitative
understanding of the stretch modulus of these tubes we carried out
nonequilibrium Steered Molecular Dynamics (SMD). The linear part of the force
extension plot gives stretch modulus in the range of 6500 pN for 6HB without
pillars which increases to 11,000 pN for tubes with three pillars. The values
of the stretch modulus calculated from contour length distributions obtained
from equilibrium MD simulations are similar to those obtained from
nonequilibrium SMD simulations. The addition of pillars makes these DNTs very
rigid.Comment: Published in ACS Nan
Haigus, mis pÔhjustas uue meditsiinieriala vÀljakujunemise
PoliomĂŒeliit on viirushaigus, mis vĂ”ib pĂ”hjustada ka jĂ€semete lĂ”tvu halvatusi, bulbaarparalĂŒĂŒsi ja hingamispuudulikkust. 19. sajandi 80. aastatel ja 20. sajandi esimesel poolel puhkesid poliomĂŒeliidiepideemiad Euroopas ja USAs. Hingamispuudulikkuse raviks konstrueeriti 1927. aastal esimene respiraator â nn raudne kops, mis vĂ”imaldas pikaajaliselt ravida hingamispuudulikkusega haigeid. BulbaarparalĂŒĂŒsi korral hakati laialdaselt kasutama trahheostoomiat. Oluliselt paranesid hingamispuudulikkusega haigete ravi vĂ”imalused vahelduva positiivrĂ”huga hingamisaparaatide kasutuselevĂ”tuga intratrahheaalseks ventilatsiooniks 1948. aastal ja mahuprintsiibil töötava Engströmi respiraatori rakendamisega. 1953. aastal avati Kopenhaagenis maailma esimene intensiivraviosakond. Massilise vaktsineerimise ja poliomĂŒeliidi likvideerimise jĂ€rel hakati saadud kogemusi rakendama kĂ”ikide kriitilises seisundis haigete ravis.
Eesti Arst 2009; 88(5):376â38
2012 MLA Small Business, Big Returns
As librarians, more often than not, we are thrust into situations where we know little, and are expected to come back with the perfect catch of the day. Business research waters are murky, but take heart; you are not alone! Come learn from some of Michigan's most successful academic and public business librarians about how they serve the public. This presentation was from the Kresge Business Administration Library (Ross School of Business at the University of Michigan) perspective.http://deepblue.lib.umich.edu/bitstream/2027.42/90943/1/Seeman_BusinessLibrarians_ServingPublicatLarge_2012.ppthttp://deepblue.lib.umich.edu/bitstream/2027.42/90943/2/Seeman_BusinessLibrarians_ServingPublicatLarge_2012.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/90943/3/Additional Comments_MLA2012_Small_Business_Big_Returns.pd
Locally Adaptive Optimization: Adaptive Seeding for Monotone Submodular Functions
The Adaptive Seeding problem is an algorithmic challenge motivated by
influence maximization in social networks: One seeks to select among certain
accessible nodes in a network, and then select, adaptively, among neighbors of
those nodes as they become accessible in order to maximize a global objective
function. More generally, adaptive seeding is a stochastic optimization
framework where the choices in the first stage affect the realizations in the
second stage, over which we aim to optimize.
Our main result is a -approximation for the adaptive seeding
problem for any monotone submodular function. While adaptive policies are often
approximated via non-adaptive policies, our algorithm is based on a novel
method we call \emph{locally-adaptive} policies. These policies combine a
non-adaptive global structure, with local adaptive optimizations. This method
enables the -approximation for general monotone submodular functions
and circumvents some of the impossibilities associated with non-adaptive
policies.
We also introduce a fundamental problem in submodular optimization that may
be of independent interest: given a ground set of elements where every element
appears with some small probability, find a set of expected size at most
that has the highest expected value over the realization of the elements. We
show a surprising result: there are classes of monotone submodular functions
(including coverage) that can be approximated almost optimally as the
probability vanishes. For general monotone submodular functions we show via a
reduction from \textsc{Planted-Clique} that approximations for this problem are
not likely to be obtainable. This optimization problem is an important tool for
adaptive seeding via non-adaptive policies, and its hardness motivates the
introduction of \emph{locally-adaptive} policies we use in the main result
- âŠ