University of Colorado Boulder

About: University of Colorado Boulder is a education organization based out in Boulder, Colorado, United States. It is known for research contribution in the topics: Population & Galaxy. The organization has 48794 authors who have published 115151 publications receiving 5387328 citations. The organization is also known as: CU Boulder & UCB.

Scalable-manufactured randomized glass-polymer hybrid metamaterial for daytime radiative cooling

Abstract: Passive radiative cooling draws heat from surfaces and radiates it into space as infrared radiation to which the atmosphere is transparent. However, the energy density mismatch between solar irradiance and the low infrared radiation flux from a near-ambient-temperature surface requires materials that strongly emit thermal energy and barely absorb sunlight. We embedded resonant polar dielectric microspheres randomly in a polymeric matrix, resulting in a metamaterial that is fully transparent to the solar spectrum while having an infrared emissivity greater than 0.93 across the atmospheric window. When backed with a silver coating, the metamaterial shows a noontime radiative cooling power of 93 watts per square meter under direct sunshine. More critically, we demonstrated high-throughput, economical roll-to-roll manufacturing of the metamaterial, which is vital for promoting radiative cooling as a viable energy technology.

Are Good Texts Always Better? Interactions of Text Coherence, Background Knowledge, and Levels of Understanding in Learning From Text

Abstract: Two experiments, theoretically motivated by the construction-integration model of text comprehension (W. Kintsch, 1988), investigated the role of text coherence in the comprehension of science texts. In Experiment 1, junior high school students' comprehension of one of three versions of a biology text was examined via free recall, written questions, and a key-word sorting task. This study demonstrates advantages for globally coherent text and for more explanatory text. In Experiment 2, interactions among local and global text coherence, readers' background knowledge, and levels of understanding were examined. Using the same methods as in Experiment 1, we examined students' comprehension of one of four versions of a text, orthogonally varying local and global coherence. We found that readers who know little about the domain of the text benefit from a coherent text, whereas high-knowledge readers benefit from a minimally coherent text. We argue that the poorly written text forces the knowledgeable readers t...

Age differences in sensation seeking and impulsivity as indexed by behavior and self-report: evidence for a dual systems model.

Abstract: It has been hypothesized that sensation seeking and impulsivity, which are often conflated, in fact develop along different timetables and have different neural underpinnings, and that the difference in their timetables helps account for heightened risk taking during adolescence. In order to test these propositions, the authors examined age differences in sensation seeking and impulsivity in a socioeconomically and ethnically diverse sample of 935 individuals between the ages of 10 and 30, using self-report and behavioral measures of each construct. Consistent with the authors' predictions, age differences in sensation seeking, which are linked to pubertal maturation, follow a curvilinear pattern, with sensation seeking increasing between 10 and 15 and declining or remaining stable thereafter. In contrast, age differences in impulsivity, which are unrelated to puberty, follow a linear pattern, with impulsivity declining steadily from age 10 on. Heightened vulnerability to risk taking in middle adolescence may be due to the combination of relatively higher inclinations to seek excitement and relatively immature capacities for self-control that are typical of this period of development.

Low-Temperature Al2O3 Atomic Layer Deposition

Abstract: Al2O3 films were deposited by atomic layer deposition (ALD) at temperatures as low as 33 °C in a viscous-flow reactor using alternating exposures of Al(CH3)3 (trimethylaluminum [TMA]) and H2O. Low-temperature Al2O3 ALD films have the potential to coat thermally fragile substrates such as organic, polymeric, or biological materials. The properties of low-temperature Al2O3 ALD films were investigated versus growth temperature by depositing films on Si(100) substrates and quartz crystal microbalance (QCM) sensors. Al2O3 film thicknesses, growth rates, densities, and optical properties were determined using surface profilometry, atomic force microscopy (AFM), QCM, and spectroscopic ellipsometry. Al2O3 film densities were lower at lower deposition temperatures. Al2O3 ALD film densities were 3.0 g/cm3 at 177 °C and 2.5 g/cm3 at 33 °C. AFM images showed that Al2O3 ALD films grown at low temperatures were very smooth with a root-mean-squared (RMS) roughness of only 4 ± 1 A. Current−voltage and capacitance−voltage...

Emergence of broadband Rayleigh waves from correlations of the ambient seismic noise.

Abstract: [1] We demonstrate that the coherent information about the Earth structure can be extracted from the ambient seismic noise We compute cross-correlations of vertical component records of several days of seismic noise at different pairs of stations separated by distances from about one hundred to more than two thousand kilometers Coherent broadband dispersive wavetrains clearly emerge with group velocities similar to those predicted from the global Rayleigh-wave tomographic maps that have been constrained using ballistic surface waves Those results show that coherent Rayleigh waves can be extracted from the ambient seismic noise and that their dispersion characteristics can be measured in a broad range of periods This provides a source for new types of surface-wave measurements that can be obtained for numerous paths that could not be sampled with the ballistic waves and, therefore, can significantly improve the resolution of seismic images