22 research outputs found
Catalysis from the bottom-up
Catalysis, the acceleration of chemical reactions by molecules that are not
consumed in the process, is essential to living organisms but currently absent
in physical systems that aspire to emulate biological functionalities with
artificial components. Here we demonstrate how to design a catalyst using
spherical building blocks interacting via programmable potentials, and show
that a minimal catalyst design, a rigid dimer, can accelerate a ubiquitous
elementary reaction, the cleaving of a bond. By combining coarse-grained
molecular dynamics simulations and theory, and by comparing the mean reaction
time in the presence and absence of the catalyst, we derive geometrical and
physical constraints for its design and determine the reaction conditions under
which catalysis emerges in the system. The framework and design rules that we
introduce are general and can be applied to experimental systems on a wide
range of scales, from micron size DNA-coated colloids to centimeter size
magnetic handshake materials, opening the door to the realization of
self-regulated artificial systems with bio-inspired functionalities.Comment: 8 pages, 4 figures. Submitte
Memory formation in matter
Memory formation in matter is a theme of broad intellectual relevance; it
sits at the interdisciplinary crossroads of physics, biology, chemistry, and
computer science. Memory connotes the ability to encode, access, and erase
signatures of past history in the state of a system. Once the system has
completely relaxed to thermal equilibrium, it is no longer able to recall
aspects of its evolution. Memory of initial conditions or previous training
protocols will be lost. Thus many forms of memory are intrinsically tied to
far-from-equilibrium behavior and to transient response to a perturbation. This
general behavior arises in diverse contexts in condensed matter physics and
materials: phase change memory, shape memory, echoes, memory effects in
glasses, return-point memory in disordered magnets, as well as related contexts
in computer science. Yet, as opposed to the situation in biology, there is
currently no common categorization and description of the memory behavior that
appears to be prevalent throughout condensed-matter systems. Here we focus on
material memories. We will describe the basic phenomenology of a few of the
known behaviors that can be understood as constituting a memory. We hope that
this will be a guide towards developing the unifying conceptual underpinnings
for a broad understanding of memory effects that appear in materials
Memory formation in Matter
Memory formation in matter is a theme of broad intellectual relevance; it sits at the interdisciplinary crossroads of physics, biology, chemistry, and computer science. Memory connotes the ability to encode, access, and erase signatures of past history in the state of a system. Once the system has completely relaxed to thermal equilibrium, it is no longer able to recall aspects of its evolution. The memory of initial conditions or previous training protocols will be lost. Thus many forms of memory are intrinsically tied to far-from-equilibrium behavior and to transient response to a perturbation. This general behavior arises in diverse contexts in condensed-matter physics and materials, including phase change memory, shape memory, echoes, memory effects in glasses, return-point memory in disordered magnets, as well as related contexts in computer science. Yet, as opposed to the situation in biology, there is currently no common categorization and description of the memory behavior that appears to be prevalent throughout condensed-matter systems. Here the focus is on material memories. The basic phenomenology of a few of the known behaviors that can be understood as constituting a memory will be described. The hope is that this will be a guide toward developing the unifying conceptual underpinnings for a broad understanding of memory effects that appear in materials
Contact Changes near Jamming
We probe the onset and effect of contact changes in soft harmonic particle
packings which are sheared quasistatically. We find that the first contact
changes are the creation or breaking of contacts on a single particle. We
characterize the critical strain, statistics of breaking versus making a
contact, and ratio of shear modulus before and after such events, and explain
their finite size scaling relations. For large systems at finite pressure, the
critical strain vanishes but the ratio of shear modulus before and after a
contact change approaches one: linear response remains relevant in large
systems. For finite systems close to jamming the critical strain also vanishes,
but here linear response already breaks down after a single contact change.Comment: 5 pages, 4 figure
Localization behavior of vibrational modes in granular packings
We study the localization of vibrational modes of frictionless granular
media. We introduce a new method, motivated by earlier work on non-Hermitian
quantum problems, which works well both in the localized regime where the
localization length is much less than the linear size and in the
regime grater or of order when modes are extended throughout our
finite system. Our very lowest frequency modes show "quasi-localized"
resonances away from the jamming point; the spatial extent of these regions
increases as the jamming point is approached, as expected theoretically.
Throughout the remaining frequency range, our data show no signature of the
nearness of the jamming point and collapse well when properly rescaled with the
system size. Using Random Matrix Theory we derive the scaling relation ~
for the regime >> in dimensions.Comment: 6 pages, 7 figure
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Size limits of self-assembled colloidal structures made using specific interactions
We establish size limitations for assembling structures of controlled size and shape out of colloidal particles with short-ranged interactions. Through simulations we show that structures with highly variable shapes made out of dozens of particles can form with high yield, as long as each particle in the structure binds only to the particles in their local environment. To understand this, we identify the excited states that compete with the ground-state structure and demonstrate that these excited states have a completely topological characterization, valid when the interparticle interactions are short-ranged. This allows complete enumeration of the energy landscape and gives bounds on how large a colloidal structure can assemble with high yield. For large structures the yield can be significant, even with hundreds of particles.Engineering and Applied SciencesMathematicsPhysic