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While numerous crystalline Si allotropes have been predicted in recent years and, in several instances, synthesized under high pressure, the exploration of Si phases with a lower density than conventional diamond Si (d-Si) is still in its infancy. Theoretical calculations on the electronic properties of these expanded Si forms suggest that, unlike the most stable d-Si structure, many may possess direct or quasi-direct bandgaps and only exhibit slightly higher formation energies than d-Si. The few that have been synthesized already display exciting optical properties, making them promising candidates for optoelectronic and photovoltaic applications. Their unique open-framework, guest–host structures enable distinctive interactions between Si and interstitial guest/dopant atoms, offering exciting potentials in spintronics, energy storage, and bio/medical technologies. In this Perspective, we provide an introduction and overview of the latest theoretical and experimental advancements in low-density Si allotropes, emphasizing their potential in various electronic and energy-related applications. This work also highlights the critical challenges and future directions for the continued development of these Si allotropes for next-generation technological applications. 

Type II Si clathrate is a Si-based, crystalline alternative to diamond silicon with interesting optoelectronic properties. Here, a pulsed electron paramagnetic resonance study of the spin dynamics of sodium-doped, type II NaxSi136 silicon clathrate films is reported. Focusing on the hyperfine lines of isolated Na atoms, the temperature dependence of the electron spin dynamics is examined from 6 to 25 K. The measurements exhibit multi-exponential decay, indicating multiple spin relaxation rates in the system. As expected, spin relaxation time (T1) increases rapidly with decreasing temperature, reaching ∼300 μs at 6.4 K. The phase memory (TM) shows less temperature dependence with a value of ∼3 μs at the same temperature. The temperature dependence of T1 exhibits Arrhenius behavior in the measurement range consistent with an Orbach pathway. There are strong similarities to the spin behavior of other defect donors in diamond silicon. The results provide insights into the potential of Si clathrates for spin-based applications. 

Anthropologists recognize the importance of conceptualizing health in the context of the mutually evolving nature of biology and culture through the biocultural approach, but biocultural anthropological perspectives of infectious diseases and their impacts on humans (and vice versa) through time are relatively underrepresented. Tuberculosis (TB) has been a constant companion of humans for thousands of years and has heavily influenced population health in almost every phase of cultural and demographic evolution. TB in human populations has been dramatically influenced by behavior, demographic and epidemiological shifts, and other comorbidities through history. This paper critically discusses TB and some of its major comorbidities through history within a biocultural framework to show how transitions in human demography and culture affected the disease-scape of TB. In doing so, I address the potential synthesis of biocultural and epidemiological transition theory to better comprehend the mutual evolution of infectious diseases and humans.