Encoding multistate charge order and chirality in endotaxial heterostructures.

High-density phase change memory (PCM) storage is proposed for materials with multiple intermediate resistance states, which have been observed in 1T-TaS2 due to charge density wave (CDW) phase transitions. However, the metastability responsible for this behavior makes the presence of multistate switching unpredictable in TaS2 devices. Here, we demonstrate the fabrication of nanothick verti-lateral H-TaS2/1T-TaS2 heterostructures in which the number of endotaxial metallic H-TaS2 monolayers dictates the number of resistance transitions in 1T-TaS2 lamellae near room temperature. Further, we also observe optically active heterochirality in the CDW superlattice structure, which is modulated in concert with the resistivity steps, and we show how strain engineering can be used to nucleate these polytype conversions. This work positions the principle of endotaxial heterostructures as a promising conceptual framework for reliable, non-volatile, and multi-level switching of structure, chirality, and resistance.

Imaging Assessment of Ectopic Gas Collections.

Ectopic gas is defined as the presence of gas in abnormal locations, that is, outside the aerodigestive tract. It constitutes a common radiologic finding associated with a wide range of disorders. Although it is usually an innocuous and self-limited condition, it should prompt a search for the underlying cause, given that the clinical significance of ectopic gas varies from benign to life threatening, depending on the site involved and the rate of accumulation. To ensure optimal management of each case, the origin of ectopic gas should be determined. The search for its exact location and underlying cause often represents a challenge, as air can be depicted distant from its point of origin because of fascial interconnectivity. Thorough knowledge of anatomic compartments facilitates quick identification of the cause and contributes to a prompt diagnosis. Likewise, radiologists should be familiar with the alarm signs associated with severe conditions. Imaging studies are essential to help the radiologist confirm the diagnosis of ectopic gas, determine its precise location and extension, identify severe cases, exclude associated complications, and monitor evolution. CT is the modality of choice in the imaging assessment of ectopic gas. In this review, the authors discuss the different causes of ectopic gas with an etiopathogenic approach to describe the myriad processes that might give rise to this condition. In addition, alarm signs associated with potentially fatal ectopic gas are described and depicted. ©RSNA, 2020.