3,319 research outputs found
Social contagions on interdependent lattice networks
Although an increasing amount of research is being done on the dynamical processes on interdependent spatial networks, knowledge of how interdependent spatial networks influence the dynamics of social contagion in them is sparse. Here we present a novel non-Markovian social contagion model on interdependent spatial networks composed of two identical two-dimensional lattices. We compare the dynamics of social contagion on networks with different fractions of dependency links and find that the density of final recovered nodes increases as the number of dependency links is increased. We use a finite-size analysis method to identify the type of phase transition in the giant connected components (GCC) of the final adopted nodes and find that as we increase the fraction of dependency links, the phase transition switches from second-order to first-order. In strong interdependent spatial networks with abundant dependency links, increasing the fraction of initial adopted nodes can induce the switch from a first-order to second-order phase transition associated with social contagion dynamics. In networks with a small number of dependency links, the phase transition remains second-order. In addition, both the second-order and first-order phase transition points can be decreased by increasing the fraction of dependency links or the number of initially-adopted nodes.This work was partially supported by National Natural Science Foundation of China (Grant Nos 61501358, 61673085), and the Fundamental Research Funds for the Central Universities. (61501358 - National Natural Science Foundation of China; 61673085 - National Natural Science Foundation of China; Fundamental Research Funds for the Central Universities)Published versio
Dynamically Stable Radiation Pressure Propulsion of Flexible Lightsails for Interstellar Exploration
Lightsail spacecraft, propelled to relativistic velocities via photon
pressure using high power density laser radiation, offer a potentially new
route to space exploration within and beyond the solar system, extending to
interstellar distances. Such missions will require meter-scale lightsails of
submicron thickness, posing substantial challenges for materials science and
engineering. We analyze the structural and photonic design of flexible
lightsails, developing a mesh-based multiphysics simulator based on linear
elastic theory, treating the lightsail as a flexible membrane rather than a
rigid body. We find that flexible lightsail membranes can be spin stabilized to
prevent shape collapse during acceleration, and that certain lightsail shapes
and designs offer beam-riding stability despite the deformations caused by
photon pressure and thermal expansion. Excitingly, nanophotonic lightsails
based on planar silicon nitride membranes patterned with suitably designed
optical metagratings exhibit both mechanically and dynamically stable
propulsion along the pump laser axis. These advances suggest that laser-driven
acceleration of membrane-like lightsails to the relativistic speeds needed to
access interstellar distances is conceptually feasible, and that fabrication of
such lightsails may be within the reach of modern microfabrication technology.Comment: 14 pages, 6 figures; plus 18-page SI with figures and linked video
SINCO: A Novel structural regularizer for image compression using implicit neural representations
Implicit neural representations (INR) have been recently proposed as deep
learning (DL) based solutions for image compression. An image can be compressed
by training an INR model with fewer weights than the number of image pixels to
map the coordinates of the image to corresponding pixel values. While
traditional training approaches for INRs are based on enforcing pixel-wise
image consistency, we propose to further improve image quality by using a new
structural regularizer. We present structural regularization for INR
compression (SINCO) as a novel INR method for image compression. SINCO imposes
structural consistency of the compressed images to the groundtruth by using a
segmentation network to penalize the discrepancy of segmentation masks
predicted from compressed images. We validate SINCO on brain MRI images by
showing that it can achieve better performance than some recent INR methods
Self-Stabilizing Silicon Nitride Lightsails
We report a design for a microscopic lightsail prototype that allows for passive stabilization in the radiation-pressure dominated regime. Stable dynamics of our silicon nitride structure are predicted for initial tilts of up to ±10°
Singlet Oxygen Chemistry in Water:  A Porous Vycor GlassSupported Photosensitizer
Singlet molecular oxygen [1O2 (1Δg)] is generated cleanly in aqueous solution upon irradiation of a heterogeneous complex, meso-tetra(N-methyl-4-pyridyl)porphine (1) adsorbed onto porous Vycor glass (PVG). The cationic photosensitizer 1 tightly binds onto PVG and gives a stable material, which does not dissociate 1 into the surrounding aqueous phase. The production of 1O2 was measured by monitoring the time-resolved 1O2 (1Δg) phosphorescence at 1270 nm. Indirect analysis of 1O2 generation was also carried out with the photooxidation oftrans-2-methyl-2-pentenoate anion, which afforded the corresponding hydroperoxide. Sensitizer-1-impregnated PVG gives rise to a new singlet oxygen generator but more importantly provides a heterogeneous system for use in water
Masked alkynes for synthesis of threaded carbon chains
Polyynes are chains of sp1 carbon atoms with alternating single and triple bonds. As they become longer, they evolve towards carbyne, the 1D allotrope of carbon, and they become increasingly unstable. It has been anticipated that long polyynes could be stabilized by supramolecular encapsulation, by threading them through macrocycles to form polyrotaxanes—but, until now, polyyne polyrotaxanes with many threaded macrocycles have been synthetically inaccessible. Here we show that masked alkynes, in which the C≡C triple bond is temporarily coordinated to cobalt, can be used to synthesize polyrotaxanes, up to the C68 [5]rotaxane with 34 contiguous triple bonds and four threaded macrocycles. This is the length regime at which the electronic properties of polyynes converge to those of carbyne. Cyclocarbons constitute a related family of molecular carbon allotropes, and cobalt-masked alkynes also provide a route to [3]catenanes and [5]catenanes built around cobalt complexes of cyclo[40]carbon and cyclo[80]carbon, respectively
Direct Radiation Pressure Measurements for Lightsail Membranes
Ultrathin lightsails propelled by laser radiation pressure to relativistic
speeds are currently the most promising route for flyby-based exoplanet
exploration. However, there has been a notable lack of experimental
characterization of key parameters essential for lightsail propulsion.
Therefore, a model platform for optomechanical characterization of lightsail
prototypes made from realistic materials is needed. We propose an approach for
simultaneous measurement of optical forces and driving powers, which
capitalizes on the multiphysics dynamics induced by the driving laser beam. By
modelling the lightsail with a 50-nm thick silicon nitride membrane suspended
by compliant micromechanical springs, we quantify force from off-resonantly
driven displacement and power from heating-induced mechanical mode softening.
This approach allows us to calibrate the measured forces to the driving powers
by operating the device as a mechanical bolometer. We report radiation pressure
forces of 80 fN using a collimated pump beam of 100 W/cm2 and noise-robust
common-path interferometry. As lightsails will inevitably experience non-normal
forces, we quantify the effects of incidence angle and spot size on the optical
force and explain the nonintuitive trend by edge scattering. Our results
provide a framework for comprehensive lightsail characterization and laboratory
optomechanical manipulation of macroscopic objects by radiation pressure
forces
SARS-CoV-2 RapidPlex: A Graphene-Based Multiplexed Telemedicine Platform for Rapid and Low-Cost COVID-19 Diagnosis and Monitoring
The COVID-19 pandemic is an ongoing global challenge for public health systems. Ultrasensitive and early identification of infection is critical in preventing widespread COVID-19 infection by presymptomatic and asymptomatic individuals, especially in the community and in-home settings. We demonstrate a multiplexed, portable, wireless electrochemical platform for ultra-rapid detection of COVID-19: the SARS-CoV-2 RapidPlex. It detects viral antigen nucleocapsid protein, IgM and IgG antibodies, as well as the inflammatory biomarker C-reactive protein, based on our mass-producible laser-engraved graphene electrodes. We demonstrate ultrasensitive, highly selective, and rapid electrochemical detection in the physiologically relevant ranges. We successfully evaluated the applicability of our SARS-CoV-2 RapidPlex platform with COVID-19-positive and COVID-19-negative blood and saliva samples. Based on this pilot study, our multiplexed immunosensor platform may allow for high-frequency at-home testing for COVID-19 telemedicine diagnosis and monitoring
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SARS-CoV-2 RapidPlex: A Graphene-Based Multiplexed Telemedicine Platform for Rapid and Low-Cost COVID-19 Diagnosis and Monitoring
The COVID-19 pandemic is an ongoing global challenge for public health systems. Ultrasensitive and early identification of infection is critical in preventing widespread COVID-19 infection by presymptomatic and asymptomatic individuals, especially in the community and in-home settings. We demonstrate a multiplexed, portable, wireless electrochemical platform for ultra-rapid detection of COVID-19: the SARS-CoV-2 RapidPlex. It detects viral antigen nucleocapsid protein, IgM and IgG antibodies, as well as the inflammatory biomarker C-reactive protein, based on our mass-producible laser-engraved graphene electrodes. We demonstrate ultrasensitive, highly selective, and rapid electrochemical detection in the physiologically relevant ranges. We successfully evaluated the applicability of our SARS-CoV-2 RapidPlex platform with COVID-19-positive and COVID-19-negative blood and saliva samples. Based on this pilot study, our multiplexed immunosensor platform may allow for high-frequency at-home testing for COVID-19 telemedicine diagnosis and monitoring
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