Michigan Technological University

About: Michigan Technological University is a education organization based out in Houghton, Michigan, United States. It is known for research contribution in the topics: Population & Volcano. The organization has 8023 authors who have published 17422 publications receiving 481780 citations. The organization is also known as: MTU & Michigan Tech.

Photoaging and stabilization of rigid PVC/wood-fiber composites

Abstract: Ultraviolet (UV) weathering performance of unpigmented and rutile titanium dioxide pigmented rigid polyvinyl chloride (PVC)/wood-fiber composites has been studied. The composite samples were manufactured by dry-blending PVC, wood fibers, and other processing additives in a high-intensity mixer. The dry-blended compounds were extruded and compression molded into panel samples. The manufactured samples were artificially weathered using laboratory accelerated UV tests. Composite samples were exposed to 340-nm fluorescent UV lamps and assessed every 200 h, for a total of 1200 h of accelerated weathering. Each assessment consisted of a visual examination of surface roughness or erosion, a contact angle measurement, a FTIR collection, and a color measurement. The experimental results indicated that wood fibers are effective sensitizers and that their incorporation into a rigid PVC matrix has a deleterious effect on the ability of the matrix to resist degradation caused ultraviolet irradiation. The light stability of these composites could be improved quite efficiently with the addition of rutile titanium dioxide photoactive pigment during formulation. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 1943–1950, 2001

Scale-dependent droplet clustering in turbulent clouds

Abstract: The current understanding of fundamental processes in atmospheric clouds, such as nucleation, droplet growth, and the onset of precipitation (collision–coalescence), is based on the assumption that droplets in undiluted clouds are distributed in space in a perfectly random manner, i.e. droplet positions are independently distributed with uniform probability. We have analysed data from a homogeneous cloud core to test this assumption and gain an understanding of the nature of droplet transport. This is done by examining one-dimensional cuts through clouds, using a theory originally developed for x-ray scattering by liquids, and obtaining statistics of droplet spacing. The data reveal droplet clustering even in cumulus cloud cores free of entrained ambient air. By relating the variance of droplet counts to the integral of the pair correlation function, we detect a systematic, scale-dependent clustering signature. The extracted signal evolves from sub- to super-Poissonian as the length scale increases. The sub-Poisson tail observed below mm-scales is a result of finite droplet size and instrument resolution. Drawing upon an analogy with the hard-sphere potential from the theory of liquids, this sub-Poisson part of the signal can be effectively removed. The remaining part displays unambiguous clustering at mm- and cm-scales. Failure to detect this phenomenon until now is a result of the previously unappreciated cumulative nature, or ‘memory,’ of the common measures of droplet clustering.

Multiple Galactic Sources with Emission Above 56 TeV Detected by HAWC

Abstract: We present the first catalog of gamma-ray sources emitting above 56 and 100 TeV with data from the High Altitude Water Cherenkov Observatory, a wide field-of-view observatory capable of detecting gamma rays up to a few hundred TeV. Nine sources are observed above 56 TeV, all of which are likely galactic in origin. Three sources continue emitting past 100 TeV, making this the highest-energy gamma-ray source catalog to date. We report the integral flux of each of these objects. We also report spectra for three highest-energy sources and discuss the possibility that they are PeVatrons.