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Latest articles for Reports on Progress in Physics
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Coupled infectious disease and behavior dynamics. A review of model assumptions
To comprehend the dynamics of infectious disease transmission, it is imperative to incorporate human protective behavior into models of disease spreading. While models exist for both infectious disease and behavior dynamics independently, the integration of these aspects has yet to yield a cohesive body of literature. Such an integration is crucial for gaining insights into phenomena like the rise of infodemics, the polarization of opinions regarding vaccines, and the dissemination of conspiracy theories during a pandemic. We make a threefold contribution. First, we introduce a framework to describe models coupling infectious disease and behavior dynamics, delineating four distinct update functions. Reviewing existing literature, we highlight a substantial diversity in the implementation of each update function. This variation, coupled with a dearth of model comparisons, renders the literature hardly informative for researchers seeking to develop models tailored to specific populations, infectious diseases, and forms of protection. Second, we advocate an approach to comparing models’ assumptions about human behavior, the model aspect characterized by the strongest disagreement. Rather than representing the psychological complexity of decision-making, we show that ‘influence-response functions’ allow one to identify which model differences generate different disease dynamics and which do not, guiding both model development and empirical research testing model assumptions. Third, we propose recommendations for future modeling endeavors and empirical research aimed at selecting models of coupled infectious disease and behavior dynamics. We underscore the importance of incorporating empirical approaches from the social sciences to propel the literature forward.
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Searches for exotic spin-dependent interactions with spin sensors
Numerous theories have postulated the existence of exotic spin-dependent interactions beyond the Standard Model of particle physics. Spin-based quantum sensors, which utilize the quantum properties of spins to enhance measurement precision, emerge as powerful tools for probing these exotic interactions. These sensors encompass a wide range of technologies, such as optically pumped magnetometers, atomic comagnetometers, spin masers, nuclear magnetic resonance, spin amplifiers, and nitrogen-vacancy centers. These technologies stand out for their ultrahigh sensitivity, compact tabletop design, and cost-effectiveness, offering complementary approaches to the large-scale particle colliders and astrophysical observations. This article reviews the underlying physical principles of various spin sensors and highlights the recent theoretical and experimental progress in the searches for exotic spin-dependent interactions with these quantum sensors. Investigations covered include the exotic interactions of spins with ultralight dark matter, exotic spin-dependent forces, electric dipole moment, spin-gravity interactions, and among others. Ongoing and forthcoming experiments using advanced spin-based sensors to investigate exotic spin-dependent interactions are discussed.
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Nucleation kinetics and virtual melting in shear-induced structural transitions
Large shear deformations can induce structural changes within crystals, yet the microscopic kinetics underlying these transformations are difficult for experimental observation and theoretical understanding. Here, we drive shear-induced structural transitions from square ( ) lattices to triangular ( ) lattices in thin-film colloidal crystals and directly observe the accompanying kinetics with single-particle resolution inside the bulk crystal. When the oscillatory shear strain amplitude , -lattice nuclei are surrounded by a liquid layer throughout their growth due to localized shear strain at the interface. Such virtual melting at crystalline interface has been predicted in theory and simulation, but have not been observed in experiment. The mean liquid layer thickness is proportional to the shear which can be explained by the Lindemann melting criterion. This provides an alternative explanation on virtual melting.
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Spontaneous photon emission by shaped quantum electron wavepackets and the QED origin of bunched electron beam superradiance
It has been shown that the spontaneous emission rate of photons by free electrons, unlike stimulated emission, is independent of the shape or modulation of the quantum electron wavefunction (QEW). Nevertheless, here we show that the quantum state of the emitted photons is non-classical and does depend on the QEW shape. This non-classicality originates from the shape dependent off-diagonal terms of the photon density matrix. This is manifested in the Wigner distribution function and would be observable experimentally through homodyne detection techniques as a squeezing effect. Considering a scheme of electrons interaction with a single microcavity mode, we present a QED formulation of spontaneous emission by multiple modulated QEWs through a build-up process. Our findings indicate that in the case of a density modulated QEWs beam, the phase of the off-diagonal terms of the photon state emitted by the modulated QEWs is the harbinger of bunched beam superradiance, where the spontaneous emission is proportional to . This observation offers a potential for enhancement of other quantum electron interactions with quantum systems by a modulated QEWs beam carrying coherence and quantum properties of the modulation.
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Challenges faced by women and persons excluded because of their ethnicity and race in physics learning environments: review of the literature and recommendations for departments and instructors
Physics, as a discipline, has long struggled with pervasive stereotypes and biases about who is capable and can excel in it. Physics also ranks among the least diverse among all science, technology, engineering, and mathematics (STEM) disciplines, often cultivating and fostering learning environments that lack inclusivity and equity. Moreover, stereotypes about brilliance, inequitable physics learning environments and the overall physics culture not only impact the experiences and outcomes of students who major in physics, but also those from other STEM disciplines who must take physics courses. Here we undertake a narrative review, delving into research concerning diversity, equity, and inclusion within undergraduate physics education. We concentrate on the experiences of women and persons excluded due to their ethnicity or race in physics, aiming to shed light on the alarming current situation. The review begins with a few concrete examples of exclusionary experiences that research shows are common for women in physics and can reduce their interest or motivation to pursue a physics major. Then, we provide our conceptualization of equity in physics learning environments and describe the frameworks informing the perspective taken in the review. We then discuss issues related to inequities in physics learning environments, including but not limited to inequities in academic performance, participation, and persistence in physics, as well as psychological factors such as physics self-efficacy, perceived recognition, social belonging, mindset beliefs, and others. We also review research on factors commonly associated with the lack of diversity, equity, and inclusion in physics including the lack of role models, stereotypes associating physics with brilliance, and the overall prototypical culture of physics. We emphasize that addressing these systemic issues in physics requires a holistic approach. We conclude with a list of recommendations for physics departments and instructors on how they can play an important role in transforming the physics culture and making the learning environments equitable and inclusive so that all students can engage in learning physics and enjoy it while feeling supported.