1,138 research outputs found
DNA hybridization catalysts and catalyst circuits
Practically all of life's molecular processes, from chemical synthesis to replication, involve enzymes that carry out their functions through the catalysis of metastable fuels into waste products. Catalytic control of reaction rates will prove to be as useful and ubiquitous in
DNA nanotechnology as it is in biology. Here we present experimental results on the control of the decay rates of a metastable DNA "fuel". We show that the fuel complex can be induced to decay with a rate about 1600 times faster than it would decay spontaneously. The original DNA hybridization catalyst [15] achieved a maximal speed-up of roughly 30. The fuel complex discussed here can therefore serve as the basic ingredient for an improved DNA hybridization catalyst. As an example application for DNA hybridization catalysts, we propose a method for implementing arbitrary digital logic circuits
Lattice Gauge Theories at the Energy Frontier
This White Paper has been prepared as a planning document for the Division of
High Energy Physics of the U. S. Department of Energy. Recent progress in
lattice-based studies of physics beyond the standard model is summarized, and
major current goals of USQCD research in this area are presented. Challenges
and opportunities associated with the recently discovered 126 GeV Higgs-like
particle are highlighted. Computational resources needed for reaching important
goals are described. The document was finalized on February 11, 2013 with
references that are not aimed to be complete, or account for an accurate
historical record of the field.Comment: Submitted for the Snowmass 2013 e-Proceedings with 44 pages, 10
figures, and 3 table
Allocating and splitting free energy to maximize molecular machine flux
Biomolecular machines transduce between different forms of energy. These
machines make directed progress and increase their speed by consuming free
energy, typically in the form of nonequilibrium chemical concentrations.
Machine dynamics are often modeled by transitions between a set of discrete
metastable conformational states. In general, the free energy change associated
with each transition can increase the forward rate constant, decrease the
reverse rate constant, or both. In contrast to previous optimizations, we find
that in general flux is neither maximized by devoting all free energy changes
to increasing forward rate constants nor by solely decreasing reverse rate
constants. Instead the optimal free energy splitting depends on the detailed
dynamics. Extending our analysis to machines with vulnerable states (from which
they can break down), in the strong driving corresponding to in vivo cellular
conditions, processivity is maximized by reducing the occupation of the
vulnerable state.Comment: 22 pages, 7 figure
Robustness: a new SLIP model based criterion for gait transitions in bipedal locomotion
Bipedal locomotion is a phenomenon that still eludes a fundamental and
concise mathematical understanding. Conceptual models that capture some
relevant aspects of the process exist but their full explanatory power is not
yet exhausted. In the current study, we introduce the robustness criterion
which defines the conditions for stable locomotion when steps are taken with
imprecise angle of attack. Intuitively, the necessity of a higher precision
indicates the difficulty to continue moving with a given gait. We show that the
spring-loaded inverted pendulum model, under the robustness criterion, is
consistent with previously reported findings on attentional demand during human
locomotion. This criterion allows transitions between running and walking, many
of which conserve forward speed. Simulations of transitions predict Froude
numbers below the ones observed in humans, nevertheless the model
satisfactorily reproduces several biomechanical indicators such as hip
excursion, gait duty factor and vertical ground reaction force profiles.
Furthermore, we identify reversible robust walk-run transitions, which allow
the system to execute a robust version of the hopping gait. These findings
foster the spring-loaded inverted pendulum model as the unifying framework for
the understanding of bipedal locomotion.Comment: unpublished, in preparatio
Catalyzed relaxation of a metastable DNA fuel
Practically all of life's molecular processes, from chemical synthesis to replication, involve enzymes that carry out their functions through
the catalytic transformation of metastable fuels into waste products.
Catalytic control of reaction rates will prove to be as useful and
ubiquitous in nucleic-acid-based engineering as it is in biology. Here
we report a metastable DNA "fuel" and a corresponding DNA
"catalyst" that improve upon the original hybridization-based
catalyst system (Turberfield et al. Phys. Rev. Lett. 90,
118102-1118102-4) by more than 2 orders of magnitude. This is achieved
by identifying and purifying a fuel with a kinetically trapped
metastable configuration consisting of a "kissing loop" stabilized
by flanking helical domains; the catalyst strand acts by opening a
helical domain and allowing the complex to relax to its ground state by
a multistep pathway. The improved fuel/catalyst system shows a roughly
5000-fold acceleration of the uncatalyzed reaction, with each catalyst
molecule capable of turning over in excess of 40 substrates. With
k_(cat)/K_M ≈ 10^7/M/min, comparable to many protein
enzymes and ribozymes, this fuel system becomes a viable component
enabling future DNA-based synthetic molecular machines and logic
circuits. As an example, we designed and characterized a signal
amplifier based on the fuel-catalyst system. The amplifier uses a
single strand of DNA as input and releases a second strand with
unrelated sequence as output. A single input strand can catalytically
trigger the release of more than 10 output strands
Dynamically Stable 3D Quadrupedal Walking with Multi-Domain Hybrid System Models and Virtual Constraint Controllers
Hybrid systems theory has become a powerful approach for designing feedback
controllers that achieve dynamically stable bipedal locomotion, both formally
and in practice. This paper presents an analytical framework 1) to address
multi-domain hybrid models of quadruped robots with high degrees of freedom,
and 2) to systematically design nonlinear controllers that asymptotically
stabilize periodic orbits of these sophisticated models. A family of
parameterized virtual constraint controllers is proposed for continuous-time
domains of quadruped locomotion to regulate holonomic and nonholonomic outputs.
The properties of the Poincare return map for the full-order and closed-loop
hybrid system are studied to investigate the asymptotic stabilization problem
of dynamic gaits. An iterative optimization algorithm involving linear and
bilinear matrix inequalities is then employed to choose stabilizing virtual
constraint parameters. The paper numerically evaluates the analytical results
on a simulation model of an advanced 3D quadruped robot, called GR Vision 60,
with 36 state variables and 12 control inputs. An optimal amble gait of the
robot is designed utilizing the FROST toolkit. The power of the analytical
framework is finally illustrated through designing a set of stabilizing virtual
constraint controllers with 180 controller parameters.Comment: American Control Conference 201
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