Understanding thermal nature of de Sitter spacetime via inter-detector interaction

The seminar discovery by Gibbons and Hawking that a freely falling detector observes an isotropic background of thermal radiation reveals that de Sitter space is equivalent to a thermal bath at the Gibbons-Hawking temperature in Minkowski space, as far as the response rate of the detector is concerned. Meanwhile, for a static detector which is endowed with a proper acceleration with respect to the local freely-falling detectors, the temperature becomes the square root of the sum of the squared Gibbons-Hawking temperature and the squared Unruh temperature associated with the proper acceleration of the detector. Here, we demonstrate, by examining the interaction of two static detectors in the de Sitter invariant vacuum, that de Sitter space in regard to its thermal nature is unique on its own right in the sense that it is even neither equivalent to the thermal bath in Minkowski space when the static detectors become freely-falling nor to the Unruh thermal bath at the cosmological horizon where the Unruh effect dominates, insofar as the behavior of the inter-detector interaction in de Sitter space dramatically differs both from that in the Minkowski thermal bath and the Unruh thermal bath.Comment: 14 page

Quantum fluctuations of spacetime generate quantum entanglement between gravitationally polarizable subsystems

There should be quantum vacuum fluctuations of spacetime itself, if we accept that the basic quantum principles we are already familiar with apply as well to a quantum theory of gravity. In this paper, we study, in linearized quantum gravity, the quantum entanglement generation at the neighborhood of the initial time between two independent gravitationally polarizable two-level subsystems caused by fluctuating quantum vacuum gravitational fields in the framework of open quantum systems. A bath of fluctuating quantum vacuum gravitational fields serves as an environment that provides indirect interactions between the two gravitationally polarizable subsystems, which may lead to entanglement generation. We find that the entanglement generation is crucially dependent on the polarizations, i.e, they cannot get entangled in certain circumstances when the polarizations of the subsystems are different while they always can when the polarizations are the same. We also show that the presence of a boundary may render parallel aligned subsystems entangled which are otherwise unentangled in a free space. However, the presence of the boundary does not help in terms of entanglement generation if the two subsystems are vertically aligned.Comment: 18 pages, 4 figure

How do online users perceive health risks during public health emergencies? Empirical evidence from China

BackgroundThe global COVID-19 pandemic has posed a major threat to human life and health, and new media technologies have intensified the spread of risk perception.PurposeThis study aimed to explore the impact of risk information ground on online users’ perceived health risks, and further explore the mediating role of psychological distance and the moderating role of self-efficacy.MethodsA total of 25 Internet users from different provinces in China were interviewed in-depth, NVIVO.11 was used to qualitatively analyze the interview text data and construct a theoretical model. A total of 492 interviewees were recruited in order to complete a scenario questionnaire, SPSS-27 was used to perform orthogonal experiments, generate eight combinatorial scenarios, analyze demographic data, and clean and prepare data for testing hypotheses. SmartPLS 3.0 was used to test the conceptual model using the structural equation model (SEM) of the partial least squares (PLS).ResultsThe analysis of the SEM model shows that all planned hypotheses (Information fluency → Information diagnosability, Information extensibility → Information diagnosability, Information diagnosability → Psychological distance, Platform interactivity → Scenario embeddedness, Network connectivity → Scenario embeddedness, Scenario embeddedness → Psychological distance, Psychological distance → Risk perception, Psychological distance → Self-efficacy → Risk perception, Information fluency → Information diagnosability → Psychological distance → Risk perception, Information extensibility → Information diagnosability → Psychological distance → Risk perception, Platform interactivity → Scenario embeddedness → Psychological distance → Risk perception, Network connectivity → Scenario embeddedness → Psychological distance → Risk perception) are confirmed.ConclusionThis study found that the information ground factors significantly affect online users’ perceptions of health risks, psychological distance mediates the effect of information ground factors on risk perception, and self-efficacy negatively moderates the effect of psychological distance on risk perception

Probing long-range properties of vacuum altered by uniformly accelerating two spatially separated Unruh-DeWitt detectors

In a quantum sense, vacuum is not an empty void but full of virtual particles (fields). It may have long-range properties, be altered, and even undergo phase transitions. It is suggested that long-range properties of a quantum vacuum may be probed by distributing matter over a large spatial volume. Here, we study a simplest example of such, i.e., two uniformly accelerated Unruh-DeWitt detectors which are spatially separated, and examine the inter-detector interaction energy arising from the coupling between the detectors and fluctuating fields to see if novel phenomena related to the long-range properties emerge of a vacuum altered by uniformly accelerating two spatially separated detectors through it. Our results show that when the inter-detector separation is much larger than the thermal wavelength of the Unruh thermal bath, the inter-detector interaction displays a completely new behavior, which, as compared with that of the inertial detectors, is surprisingly exclusively acceleration-dependent, signaling a new phase of the vacuum in which its imprint as seen by two inertial observers seems to be completely wiped out. Moreover, we demonstrate that the inter-detector interaction in the near region can be significantly enhanced by the accelerated motion in certain circumstances, and with two Rydberg atoms as the detectors, the acceleration required for an experimentally detectable enhancement of the interaction energy can be $10^5$ times smaller than that required for the detection of the Unruh effect.Comment: 10 pages, 1 figure, 2 table

Quantum thermal field fluctuation induced corrections to the interaction between two ground-state atoms

We study the thermal corrections induced by fluctuations of thermal quantum fields to the van der Waals and Casimir-Polder interactions between two ground-state atoms. We discover a particular region, i.e., $\sqrt[4]{\lambda^3\beta}\ll L\ll \lambda$ with $L$, $\beta$ and $\lambda$ denoting the interatomic separation, the wavelength of thermal photons and the transition wavelength of the atoms respectively, where the thermal corrections remarkably render the van der Waals force, which is usually attractive, repulsive, leading to an interesting crossover phenomenon of the interatomic interaction from attractive to repulsive as the temperature increases. We also find that the thermal corrections cause significant changes to the Casimir-Polder force when the temperature is sufficiently high, resulting in an attractive force proportional to $TL^{-3}$ in the $\lambda\ll\beta\ll L$ region, with $T$ being the temperature, and a force which can be either attractive or repulsive and even vanishing in the $\beta\ll\lambda\ll L$ region depending on the interatomic separation.Comment: 20 page

Finite Element Approximations to Caputo–Hadamard Time-Fractional Diffusion Equation with Application in Parameter Identification

A finite element scheme for solving a two-timescale Hadamard time-fractional equation is discussed. We prove the error estimate without assuming the smoothness of the solution. In order to invert the fractional order, a finite-element Levenberg–Marquardt method is designed. Finally, we give corresponding numerical experiments to support the correctness of our analysis

Awayvirus:A Playful and Tangible Approach to Improve Children's Hygiene Habits in Family Education

Despite various playful and educational tools have been developed to support children's learning abilities, limited work focuses on tangible toys designed to improve and maintain children's hygiene perception, habits and awareness, as well as fostering their collaboration and social abilities in home education contexts. We developed Awayvirus to address this research and design gap, aiming to help children gain hygiene habits knowledge through tangible blocks. Our findings indicate that a playful tangible interaction method can effectively increase children's interest in learning and encourage parents to become actively involved in their children's hygiene and health education. Additionally, Awayvirus seeks to build a collaborative bridge between children and parents, promoting communication strategies while mitigating the adverse effects of the challenging the post-pandemic period