158 research outputs found
Emergence of hysteresis loop in social contagions on complex networks
Understanding the spreading mechanisms of social contagions in complex network systems has attracted much attention in the physics community. Here we propose a generalized threshold model to describe social contagions. Using extensive numerical simulations and theoretical analyses, we find that a hysteresis loop emerges in the system. Specifically, the steady state of the system is sensitive to the initial conditions of the dynamics of the system. In the steady state, the adoption size increases discontinuously with the transmission probability of information about social contagions, and trial size exhibits a non-monotonic pattern, i.e., it first increases discontinuously then decreases continuously. Finally we study social contagions on heterogeneous networks and find that network topology does not qualitatively affect our results.This work was funded in part by the National Key Research and Development Program (Grant No. 2016YFB0800602), the National Natural Science the Foundation of China (Grant Nos 61472045,61573067), and the China Scholarship Council. (2016YFB0800602 - National Key Research and Development Program; 61472045 - National Natural Science the Foundation of China; 61573067 - National Natural Science the Foundation of China; China Scholarship Council)Published versio
Floquet Chern Insulators of Light
Achieving topologically-protected robust transport in optical systems has
recently been of great interest. Most topological photonic structures can be
understood by solving the eigenvalue problem of Maxwell's equations for a
static linear system. Here, we extend topological phases into dynamically
driven nonlinear systems and achieve a Floquet Chern insulator of light in
nonlinear photonic crystals (PhCs). Specifically, we start by presenting the
Floquet eigenvalue problem in driven two-dimensional PhCs and show it is
necessarily non-Hermitian. We then define topological invariants associated
with Floquet bands using non-Hermitian topological band theory, and show that
topological band gaps with non-zero Chern number can be opened by breaking
time-reversal symmetry through the driving field. Furthermore, we show that
topological phase transitions between Floquet Chern insulators and normal
insulators occur at synthetic Weyl points in a three-dimensional parameter
space consisting of two momenta and the driving frequency. Finally, we
numerically demonstrate the existence of chiral edge states at the interfaces
between a Floquet Chern insulator and normal insulators, where the transport is
non-reciprocal and uni-directional. Our work paves the way to further exploring
topological phases in driven nonlinear optical systems and their optoelectronic
applications, and our method of inducing Floquet topological phases is also
applicable to other wave systems, such as phonons, excitons, and polaritons
Quadrupole Topological Photonic Crystals
Quadrupole topological phases, exhibiting protected boundary states that are
themselves topological insulators of lower dimensions, have recently been of
great interest. Extensions of these ideas from current tight binding models to
continuum theories for realistic materials require the identification of
quantized invariants describing the bulk quadrupole order. Here we identify the
analog of quadrupole order in Maxwell's equations for a photonic crystal (PhC)
and identify quadrupole topological photonic crystals formed through a band
inversion process. Unlike prior studies relying on threaded flux, our
quadrupole moment is quantized purely by crystalline symmetries, which we
confirm using three independent methods: analysis of symmetry eigenvalues,
numerical calculations of the nested Wannier bands, and the expectation value
of the quadrupole operator. Furthermore, through the bulk-edge correspondence
of Wannier bands, we reveal the boundary manifestations of nontrivial
quadrupole phases as quantized polarizations at edges and bound states at
corners. Finally, we relate the nontrivial corner states to the emergent
phenomena of quantized fractional corner charges and a filling anomaly as first
predicted in electronic systems. Our work paves the way to further explore
higher-order topological phases in nanophotonic systems and our method of
inducing quadrupole phase transitions is also applicable to other wave systems,
such as electrons, phonons and polaritons
Punishment diminishes the benefits of network reciprocity in social dilemma experiments
Network reciprocity has been widely advertised in theoretical studies as one of the basic cooperation-promoting mechanisms, but experimental evidence favoring this type of reciprocity was published only recently. When organized in an unchanging network of social contacts, human subjects cooperate provided the following strict condition is satisfied: The benefit of cooperation must outweigh the total cost of cooperating with all neighbors. In an attempt to relax this condition, we perform social dilemma experiments wherein network reciprocity is aided with another theoretically hypothesized cooperation-promoting mechanism—costly punishment. The results reveal how networks promote and stabilize cooperation. This stabilizing effect is stronger in a smaller-size neighborhood, as expected from theory and experiments. Contrary to expectations, punishment diminishes the benefits of network reciprocity by lowering assortment, payoff per round, and award for cooperative behavior. This diminishing effect is stronger in a larger-size neighborhood. An immediate implication is that the psychological effects of enduring punishment override the rational response anticipated in quantitative models of cooperation in networks.We thank J. H. Lee for useful discussions. M.J. and Z.W. were, respectively, supported by the Research Grant Program of Inamori Foundation and the Chinese Young 1000 Talents Plan. B.P. received support from the Slovenian Research Agency (ARRS) and the Croatian Science Foundation through Projects J5-8236 and 5349, respectively. S.H. thanks the Israel-Italian collaborative project Network Cyber Security (NECST), Israel Science Foundation, Office of Naval Research (ONR), Japan Science Foundation, and the US-Israel Binational Science Foundation and the US National Science Foundation (BSF-NSF) for financial support. The Boston University Center for Polymer Studies is supported by NSF Grants PHY-1505000, CMMI-1125290, and CHE-1213217, by Defense Threat Reduction Agency (DTRA) Grant HDTRA1-14-1-0017, and by Department of Energy (DOE) Contract DE-AC07-05Id14517. (Inamori Foundation; Chinese Young 1000 Talents Plan; J5-8236 - Slovenian Research Agency (ARRS); 5349 - Croatian Science Foundation; Israel-Italian collaborative project Network Cyber Security (NECST); Israel Science Foundation; Office of Naval Research (ONR); Japan Science Foundation; US-Israel Binational Science Foundation; US National Science Foundation (BSF-NSF); PHY-1505000 - NSF; CMMI-1125290 - NSF; CHE-1213217 - NSF; HDTRA1-14-1-0017 - Defense Threat Reduction Agency (DTRA); DE-AC07-05Id14517 - Department of Energy (DOE))Published versio
BRIDGE DEVICES FOR WIRELESS PROJECTION OF VEHICLE OPERATING SYSTEMS
Vehicles may provide an infotainment experience that is hosted by a head unit or other computing device. The head unit may execute a native operating system that provides an execution environment in which an operating system client may execute to support execution of a different operating system hosted by another computing device (e.g., a smartphone, laptop computer, tablet computer, etc.). The head unit may require that the computing device physically interconnect with the head unit as the head unit may not support wireless connections (or only support limited wireless connections in the form of bandwidth limited connection – e.g., personal area network connections, such as Bluetooth® connections). Techniques described in this disclosure provide a bridge device for enabling wireless connections between the head unit and the computing devices for wireless projection of the different operating system, where the bridge device provides the physical interconnection required by the head unit while maintaining the wireless connection with the computing device to support wireless projection of the different operating system
Geometric similarities and topological phases in surface magnon polaritons
Highly spatially-squeezed polaritons, with propagation momentum significantly
larger than free-space modes at the same frequency, enable varied and extreme
control over light-matter interaction. Compared to other polaritons, surface
magnon polaritons, the magnetic counterpart of surface phonon polaritons, have
received relatively little attention. Here, we investigate the dispersion and
properties of surface-magnon polaritons, highlighting the impact of geometric
similarities and applying them to various surface-magnon polariton devices in
both conventional and topological settings. Our theory predicts a method for
strongly localizing and significantly enhancing magnetic fields in the
microwave range and developing compact and lossless connectors capable of
interconnecting waveguides with vastly different input and output impedances.
Our work opens new avenues for manipulating magnetic fields in the microwave
regime and for exploring topological phases in polariton platforms
Characterization of ZnO Nanorods Grown on GaN Using Aqueous Solution Method
Uniformly distributed ZnO nanorods with diameter 70-100 nm and 1-2μm long have been successfully grown at low temperatures on GaN by using the inexpensive aqueous solution method. The formation of the ZnO nanorods and the growth parameters are controlled by reactant concentration, temperature and pH. No catalyst is required. The XRD studies show that the ZnO nanorods are single crystals and that they grow along the c axis of the crystal plane. The room temperature photoluminescence measurements have shown ultraviolet peaks at 388nm with high intensity, which are comparable to those found in high quality ZnO films. The mechanism of the nanorod growth in the aqueous solution is proposed. The dependence of the ZnO nanorods on the growth parameters was also investigated. While changing the growth temperature from 60°C to 150°C, the morphology of the ZnO nanorods changed from sharp tip (needle shape) to flat tip (rod shape). These kinds of structure are useful in laser and field emission application.Singapore-MIT Alliance (SMA
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