University of Massachusetts Amherst

About: University of Massachusetts Amherst is a education organization based out in Amherst Center, Massachusetts, United States. It is known for research contribution in the topics: Population & Galaxy. The organization has 37274 authors who have published 83965 publications receiving 3834996 citations. The organization is also known as: UMass Amherst & Massachusetts State College.

Tailored Assemblies of Block Copolymers in Solution: It Is All about the Process

Abstract: Block copolymers have the capacity to self-organize into a myriad of aggregate structures when placed in selective solvents, offering great promise for the construction of delivery vehicles and complex nanoscale assemblies. A key feature of these materials is their propensity to become kinetically trapped in nonequilibrium states, meaning that the structures they adopt depend sensitively on the processing route taken. While this makes it challenging to fully explore the landscape of possible morphologies, it also means that careful attention to the pathway of self-assembly can allow for remarkable control over the resulting nonequilibrium structures. In this Perspective, we highlight several recent advances in processing approaches that provide new levels of tailorability to the structures and encapsulated contents of block copolymer assemblies in solution.

MEMS-tunable dielectric metasurface lens.

Abstract: Varifocal lenses, conventionally implemented by changing the axial distance between multiple optical elements, have a wide range of applications in imaging and optical beam scanning. The use of conventional bulky refractive elements makes these varifocal lenses large, slow, and limits their tunability. Metasurfaces, a new category of lithographically defined diffractive devices, enable thin and lightweight optical elements with precisely engineered phase profiles. Here we demonstrate tunable metasurface doublets, based on microelectromechanical systems (MEMS), with more than 60 diopters (about 4%) change in the optical power upon a 1-μm movement of one metasurface, and a scanning frequency that can potentially reach a few kHz. They can also be integrated with a third metasurface to make compact microscopes (~1 mm thick) with a large corrected field of view (~500 μm or 40 degrees) and fast axial scanning for 3D imaging. This paves the way towards MEMS-integrated metasurfaces as a platform for tunable and reconfigurable optics.

Natural Resource Abundance and Economic Growth

Abstract: This paper explores whether natural resource abundance leads, other things equal, to slower growth rates. We distinguish between natural resource dependence (RD) and the natural resource endowment (RE). We estimate three models, using World Bank data on national capital stocks. In a one-equation model we show that RD has a negative effect on growth rates, apparently confirming the main results of the resource "curse" literature. RE, however, has a positive impact on growth. We then estimate a two-equation model, in which the impacts of RE are much weaker. Finally, we estimate a three-equation model, in which the impacts of natural resources on growth disappears.