919 research outputs found
Quantum-Mechanically Induced Asymmetry in the Phase Diagrams of Spin-Glass Systems
The spin-1/2 quantum Heisenberg model is studied in all spatial dimensions d
by renormalization-group theory. Strongly asymmetric phase diagrams in
temperature and antiferromagnetic bond probability p are obtained in dimensions
d \geq 3. The asymmetry at high temperatures approaching the pure ferromagnetic
and antiferromagnetic systems disappears as d is increased. However, the
asymmetry at low but finite temperatures remains in all dimensions, with the
antiferromagnetic phase receding to the ferromagnetic phase. A
finite-temperature second-order phase boundary directly between the
ferromagnetic and antiferromagnetic phases occurs in d \geq 6, resulting in a
new multicritical point at its meeting with the boundaries to the paramagnetic
phase. In d=3,4,5, a paramagnetic phase reaching zero temperature intervenes
asymmetrically between the ferromagnetic and reentrant antiferromagnetic
phases. There is no spin-glass phase in any dimension.Comment: Added discussion of second-order transitions between ordered phases,
driven by quenched disorder. 4 pages, 1 figure, 3 tables. Published versio
Infinitely Robust Order and Local Order-Parameter Tulips in Apollonian Networks with Quenched Disorder
For a variety of quenched random spin systems on an Apollonian network,
including ferromagnetic and antiferromagnetic bond percolation and the Ising
spin glass, we find the persistence of ordered phases up to infinite
temperature over the entire range of disorder. We develop a
renormalization-group technique that yields highly detailed information,
including the exact distributions of local magnetizations and local spin-glass
order parameters, which turn out to exhibit, as function of temperature,
complex and distinctive tulip patterns.Comment: 5 pages, 4 figures; updated to reflect minor changes in published
versio
Frustrated Further-Neighbor Antiferromagnetic and Electron-Hopping Interactions in the d=3 tJ Model: Finite-Temperature Global Phase Diagrams from Renormalization-Group Theory
The renormalization-group theory of the d=3 tJ model is extended to
further-neighbor antiferromagnetic or electron-hopping interactions, including
the ranges of frustration. The global phase diagram of each model is calculated
for the entire ranges of temperatures, electron densities, and
further/first-neighbor interaction strength ratios. In addition to the
\tau_{tJ} phase seen in earlier studies of the nearest-neighbor d=3 tJ model,
the \tau_{Hb} phase seen before in the d=3 Hubbard model appears both near and
away from half-filling. These distinct \tau phases potentially correspond to
different (BEC-like and BCS-like) superconducting phases.Comment: Improved figures, added discussions, added references. Published
version. 12 pages, 5 figures, 6 table
Infinitely Robust Order and Local Order-Parameter Tulips in Apollonian Networks with Quenched Disorder
For a variety of quenched random spin systems on an Apollonian network, including ferromagnetic and antiferromagnetic bond percolation and the Ising spin glass, we find the persistence of ordered phases up to infinite temperature over the entire range of disorder. We develop a renormalization-group technique that yields highly detailed information, including the exact distributions of local
magnetizations and local spin-glass order parameters, which turn out to exhibit, as function of temperature, complex and distinctive tulip patterns
Dynamics of evaporative colloidal patterning
Drying suspensions often leave behind complex patterns of particulates, as
might be seen in the coffee stains on a table. Here we consider the dynamics of
periodic band or uniform solid film formation on a vertical plate suspended
partially in a drying colloidal solution. Direct observations allow us to
visualize the dynamics of the band and film deposition, and the transition in
between when the colloidal concentration is varied. A minimal theory of the
liquid meniscus motion along the plate reveals the dynamics of the banding and
its transition to the filming as a function of the ratio of deposition and
evaporation rates. We also provide a complementary multiphase model of colloids
dissolved in the liquid, which couples the inhomogeneous evaporation at the
evolving meniscus to the fluid and particulate flows and the transition from a
dilute suspension to a porous plug. This allows us to determine the
concentration dependence of the bandwidth and the deposition rate. Together,
our findings allow for the control of drying-induced patterning as a function
of the colloidal concentration and evaporation rate.Comment: 11 pages, 7 figures, 2 table
Dynamic, viscoelasticity-driven shape change of elastomer bilayers
Thin bilayers made of elastic sheets with different strain recoveries can be
used for dynamic shape morphing through ambient stimuli, such as temperature,
mass diffusion, and light. As a fundamentally different approach to designing
temporal shape change, constituent polymer molecular features (rather than
external fields) are leveraged, specifically the viscoelasticity of gelatin
bilayers, to achieve dynamic three-dimensional (3D) curls and helical twists.
After stretching and releasing, the acquired 3D shape recovers its original
flat shape on a timescale originating from the polymer viscoelasticity. The
bilayer time-dependent curvature can be accurately predicted from hyperelastic
and viscoelastic functions using finite element analysis (FEA). FEA reveals the
nonlinear shape dynamics in space and time in quantitative agreement with
experiments. The findings present a new frontier in dynamic biomimetic
shape-morphing by exploiting intrinsic material properties in contrast with
state-of-the-art methods relying on external field variations, moving one step
closer to acquiring autonomous shape-shifting capabilities of biological
systems.Comment: For SI, see
https://drive.google.com/file/d/1MH0kURA_OiOaePDQC06Eua1aG3kkEBV4/view?usp=sharin
Diffusio-phoretic fast swelling of chemically responsive hydrogels
Acid-induced release of stored ions from polyacrylic acid hydrogels (with a
free surface fully permeable to the ion and acid flux) was observed to increase
the gel osmotic pressure that leads to rapid, temporary swelling faster than
the characteristic solvent absorption rate of the gel. Here we develop a
continuum poroelastic theory that quantitatively explains the experiments by
introducing a "gel diffusio-phoresis" mechanism: Steric repulsion between the
gel polymers and released ions can induce a diffusio-osmotic solvent intake
counteracted by the diffusio-phoretic expansion of the gel network. For
applications ranging from drug delivery to soft robotics, engineering the gel
diffusio-phoresis may enable stimuli-responsive hydrogels with amplified strain
rates and power output
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