Properties of grains derived from IRAS observations of dust

The authors used the results of Infrared Astronomy Satellite (IRAS) observations of diffuse medium dust to develop a theoretical model of the infrared properties of grains. Recent models based entirely on traditional observations of extinction and polarization include only particles whose equilibrium temperatures do not exceed 20 K in the diffuse interstellar medium. These classical grains, for which the authors have adopted the multipopulation model developed by Hong and Greenberg (1980), can explain only the emission in the IRAS 100 micron band. The measurements at shorter wavelengths (12, 25 and 60 microns) require two new particle populations. Vibrational fluorescence from aromatic molecules provides the most likely explanation for the emission observed at 12 microns, with polycyclic aeromatic hydrocarbons (PAHs) containing about 10 percent of cosmic carbon. A simplified model of the emission process shows that PAH molecules can also explain most of the emission measured by IRAS at 25 microns. The authors identified the warm particles responsible for the excess 60 microns emission with small (a approx. equals 0.01 microns) iron grains. A compilation of the available data on the optical properties of iron indicates that the diffuse medium temperature of small iron particles should be close to 50 K and implies that a large, possibly dominant, fraction of cosmic iron must be locked up in metallic particles in order to match the observed 60 microns intensities. The model matches the infrared fluxes typically observed by IRAS in the diffuse medium and can also reproduce the infrared surface brightness distribution in individual clouds. In particular, the combination of iron and classical cool grains can explain the surprising observations of the 60/100 microns flux ratio in clouds, which is either constant or increases slightly towards higher opacities. The presence of metallic grains has significant implications for the physics of the interstellar medium, including catalytic H2 formation, for which iron grains could be the main site; differences in depletion patterns between iron and other refractory elements (Mg, Si); and superparamagnetic behavior of large grains with embedded iron clusters giving rise to the observed high degree of alignment by the galactic magnetic field

What children like in elementary principals

Thesis (Ed.M.)--Boston Universit

Enhancing academic achievement and satisfaction by flipping the teacher preparation classroom

This study compared flipped classrooms versus online courses to study the effects of the two instructional methodologies on student achievement and satisfaction in an undergraduate Introduction to Education, EDUC 1301, course. Students self-matriculated in either traditional EDUC 1301 courses which were flipped or in EDUC 1301 online courses. Students\u27 final grades were used to assess student achievement in both teaching methodologies. An end-of-course student evaluation of instructor performance was used to assess students\u27 satisfaction in the courses. A casual comparative research design was used to examine the effectiveness of both teaching methodologies. There was no differences between the two instructional methodologies in student satisfaction. Students were equally satisfied in both teaching methodologies. Statistical significant differences were found, however, in the students\u27 achievement level. The percent of students in the flipped classroom who passed the courses was 92% compared with 75% achievement level in the students who passed the online courses. The number of students who passed the EDUC 1301 flipped classroom courses as presented in Table 1, page 44, and Figure 1, page 44, was 83 out of 90, resulting in an achievement level of 92%. On the contrary, 118 out of 157 students passed the EDUC 1301 online courses, as shown in Table 1, page 44, and Figure 1, page 44, representing an achievement level of 75%. The Pearson chi-square test of association yielded a chi2 of 10.99, a df = 1, and a p value of 0.0001 which was statistically significant at the 95% confidence level (p \u3c .05), Table 3, page 45. Students who self-enrolled in the flipped classrooms did statistically significantly better than those students who self-enrolled in the online courses. Instructional methodology, however, was an insignificant predictor of student satisfaction between the students in the flipped classrooms and the online courses. (PsycInfo Database Record (c) 2022 APA, all rights reserved

Dust emission from high latitude cirrus clouds

In order to study dust emission from grains in the interstellar medium, the infrared properties were analyzed in a number of isolated high latitude dust clouds which contain no dominant internal heating sources. The clouds are spatially resolved, have a simple geometry, and are mapped in the IRAS bands at 12, 25, 60, and 100 microns. For a number of these clouds, extinction data (A sub B) were obtained from starcounts. A large part (30 to 50 percent) of the infrared radiation of the clouds in the IRAS wavelength range of 8 to 130 micron is emitted in the short wavelength bands at 12 and 25 micron. The 60/100 micron ratios for the integrated fluxes of the clouds have a typical value of 0.19 + or - 0.05

Comparison of the bidirectional reflectance distribution function of various surfaces

Described is the development and use of a system to measure the Bidirectional Reflectance Distribution Function (BRDF) of various surfaces. The BRDF measurements are used in the analysis and design of optical measurement systems, such as laser anemometers. An argon ion laser (514 nm) is the light source. Preliminary results are presented for eight samples: two glossy black paints, two flat black paints, black glass, sand blasted aluminum, unworked aluminum, and a white paint. A BaSO4 white reflectance standard was used as the reference sample throughout the tests. The reflectance characteristics of these surfaces are compared

Solving the Jitter Problem in Microwave Compressed Ultrafast Electron Diffraction Instruments: Robust Sub-50 fs Cavity-Laser Phase Stabilization

We demonstrate the compression of electron pulses in a high-brightness ultrafast electron diffraction (UED) instrument using phase-locked microwave signals directly generated from a mode-locked femtosecond oscillator. Additionally, a continuous-wave phase stabilization system that accurately corrects for phase fluctuations arising in the compression cavity from both power amplification and thermal drift induced detuning was designed and implemented. An improvement in the microwave timing stability from 100 fs to 5 fs RMS is measured electronically and the long-term arrival time stability ($>$10 hours) of the electron pulses improves to below our measurement resolution of 50 fs. These results demonstrate sub-relativistic ultrafast electron diffraction with compressed pulses that is no longer limited by laser-microwave synchronization.Comment: Accepted for publication in Structural Dynamic