6,991 research outputs found
Scaling of geometric phase versus band structure in cluster-Ising models
We study the phase diagram of a class of models in which a generalized
cluster interaction can be quenched by Ising exchange interaction and external
magnetic field. We characterize the various phases through winding numbers.
They may be ordinary phases with local order parameter or exotic ones, known as
symmetry protected topologically ordered phases. Quantum phase transitions with
dynamical critical exponents z = 1 or z = 2 are found. Quantum phase
transitions are analyzed through finite-size scaling of the geometric phase
accumulated when the spins of the lattice perform an adiabatic precession. In
particular, we quantify the scaling behavior of the geometric phase in relation
with the topology and low energy properties of the band structure of the
system
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Network Topologies That Can Achieve Dual Function of Adaptation and Noise Attenuation.
Many signaling systems execute adaptation under circumstances that require noise attenuation. Here, we identify an intrinsic trade-off existing between sensitivity and noise attenuation in the three-node networks. We demonstrate that although fine-tuning timescales in three-node adaptive networks can partially mediate this trade-off in this context, it prolongs adaptation time and imposes unrealistic parameter constraints. By contrast, four-node networks can effectively decouple adaptation and noise attenuation to achieve dual function without a trade-off, provided that these functions are executed sequentially. We illustrate ideas in seven biological examples, including Dictyostelium discoideum chemotaxis and the p53 signaling network and find that adaptive networks are often associated with a noise attenuation module. Our approach may be applicable to finding network design principles for other dual and multiple functions
Dynamics of non-muscle myosin II organization into contractile networks and fibers at medial cell cortex
The cellular morphology of adhered cells depends crucially on the formation of a contractile meshwork of parallel and cross-linked stress fibers along the contacting surface. The motor activity and mini-filament assembly of non-muscle myosin II is an important component of cell-level cytoskeletal remodeling during mechanosensing. To monitor the dynamics of non-muscle myosin II, we used confocal microscopy to image cultured HeLa cells that stably express myosin regulatory light chain tagged with GFP (MRLC-GFP). MRLC-GFP was monitored in time-lapse movies at steady state and during the response of cells to varying concentrations of blebbistatin (which disrupts actomyosin stress fibers). Using image correlation spectroscopy analysis, we quantified the kinetics of disassembly and reassembly of actomyosin networks and compared to studies by other groups. This analysis suggested the following processes: myosin minifilament assembly and disassembly; aligning and contraction; myosin filament stabilization upon increasing contractile tension. Numerical simulations that include those processes capture some of the main features observed in the experiments. This study provides a framework to help interpret how different cortical myosin remodeling kinetics may contribute to different cell shape and rigidity depending on substrate stiffness. We discuss methods to monitor myosin reorganization using non-linear imaging methods
Noise control and utility: From regulatory network to spatial patterning
Stochasticity (or noise) at cellular and molecular levels has been observed
extensively as a universal feature for living systems. However, how living
systems deal with noise while performing desirable biological functions remains
a major mystery. Regulatory network configurations, such as their topology and
timescale, are shown to be critical in attenuating noise, and noise is also
found to facilitate cell fate decision. Here we review major recent findings on
noise attenuation through regulatory control, the benefit of noise via
noise-induced cellular plasticity during developmental patterning, and
summarize key principles underlying noise control
Quantum state engineering with flux-biased Josephson phase qubits by Stark-chirped rapid adiabatic passages
In this paper, the scheme of quantum computing based on Stark chirped rapid
adiabatic passage (SCRAP) technique [L. F. Wei et al., Phys. Rev. Lett. 100,
113601 (2008)] is extensively applied to implement the quantum-state
manipulations in the flux-biased Josephson phase qubits. The broken-parity
symmetries of bound states in flux-biased Josephson junctions are utilized to
conveniently generate the desirable Stark-shifts. Then, assisted by various
transition pulses universal quantum logic gates as well as arbitrary
quantum-state preparations could be implemented. Compared with the usual
PI-pulses operations widely used in the experiments, the adiabatic population
passage proposed here is insensitive the details of the applied pulses and thus
the desirable population transfers could be satisfyingly implemented. The
experimental feasibility of the proposal is also discussed.Comment: 9 pages, 4 figure
Non-equilibrium phases of Fermi gas inside a cavity with imbalanced pumping
In this work, we investigate the non-equilibrium dynamics of one-dimensional
spinless fermions loaded in a cavity with imbalanced pumping lasers. Our study
is motivated by previous work on a similar setup using bosons, and we explore
the unique properties of fermionic systems in this context. By considering the
imbalance in the pumping, we find that the system exhibits multiple
superradiant steady phases and an unstable phase. Furthermore, by making use of
the hysteresis structure of superradiant phases, we propose a unidirectional
topological pumping. Unlike the usual topological pumping in which the driving
protocol breaks time reversal symmetry, the driving protocol can be time
reversal invariant in our proposal.Comment: 7 pages, 12 figure
Electromagnetic Scattering by Open-Ended Cavities: An Analysis Using Precorrected-FFT Approach
In this paper, the precorrected-FFT method is used to solve the electromagnetic scattering from two-dimensional cavities of arbitrary shape. The integral equation is discretized by the method of moments and the resultant matrix equation is solved iteratively by the generalized conjugate residual method. Instead of directly computing the matrix-vector multiplication, which requires N² operations, this approach reduces the computation complexity to O(N log N) as well as avoids the storage of large matrices. At the same time, a technique known as the complexifying k is applied to accelerate the convergence of the iterative method in solving this resonance problem. Some examples are considered and excellent agreements of radar cross sections between these computed using the present method and those from the direct solution are observed, demonstrating the feasibility and efficiency of the present method.Singapore-MIT Alliance (SMA
Relaying systems with reciprocity mismatch : impact analysis and calibration
Cooperative beamforming can provide significant performance improvement for relaying systems with the help of the channel state information (CSI). In time-division duplexing (TDD) mode, the estimated CSI will deteriorate due to the reciprocity mismatch. In this work, we examine the impact and the calibration of the reciprocity mismatch in relaying systems. To evaluate the impact of the reciprocity mismatch for all devices, the closed-form expression of the achievable rate is first derived. Then, we analyze the performance loss caused by the reciprocity mismatch at sources, relays, and destinations respectively to show that the mismatch at relays dominates the impact. To compensate the performance loss, a two-stage calibration scheme is proposed for relays. Specifically, relays perform the intra-calibration based on circuits independently. Further, the inter-calibration based on the discrete Fourier transform (DFT) codebook is operated to improve the calibration performance by cooperation transmission, which has never been considered in previous work. Finally, we derive the achievable rate after relays perform the proposed reciprocity calibration scheme and investigate the impact of estimation errors on the system performance. Simulation results are presented to verify the analytical results and to show the performance of the proposed calibration approach
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