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Papers by George Hassel

The Physics Teacher, 2017

2020 Physics Education Research Conference Proceedings, 2020

A study of the impact of team-based learning (TBL), an active learning teaching strategy develope... more A study of the impact of team-based learning (TBL), an active learning teaching strategy developed by Larry Michaelsen of the University of Oklahoma, was conducted to determine the impact of TBL on students in introductory and upper-level physics courses. The study was designed to use institutional data to determine whether TBL increase retention of physics majors. A survey, the physics TBL survey (PTS), was developed and used to understand student experiences with TBL in the classroom. We found that TBL increased retention of physics majors overall and specifically in the critical freshmen and sophomore years. The results from the study show that students value TBL favorably for both introductory and upper-level physics courses over 8 different measures. Introductory students ranked the learning of physics, the effectiveness of the TBL format for physics courses, and the value of the team experience higher than the upper-level physics students. Finally, students indicate that TBL is a less intimidating classroom format, they appreciate instant feedback because it helps them to learn more quickly and keeps them engaged in class, they find peer explanations of new physics topics to be valuable, and they are find that the readiness assurance process keeps them motivated and accountable.

2018 Conference on Laboratory Instruction Beyond the First Year of College, 2018

Uncertainty or error analysis is an important skill to be developed throughout the undergraduate ... more Uncertainty or error analysis is an important skill to be developed throughout the undergraduate physics laboratory curriculum. Numerical estimation and propagation of measurement uncertainties are a crucial part of interpreting and reporting laboratory results. The ability to clearly identify, explain and evaluate measurement uncertainty is also an important part of the broader goal of improving student writing and to modify poor writing habits. Modern Physics Lab provides a particularly opportune time to develop error propagation in detail. This paper examines uncertainty propagation in two example lab activities.

Physical Review Physics Education Research, 2017

We present the Electricity and Magnetism Conceptual Assessment (EMCA), a new assessment aligned w... more We present the Electricity and Magnetism Conceptual Assessment (EMCA), a new assessment aligned with second-semester introductory physics courses. Topics covered include electrostatics, electric fields, circuits, magnetism, and induction. We have two motives for writing a new assessment. First, we find other assessments such as the Brief Electricity and Magnetism Assessment and the Conceptual Survey on Electricity and Magnetism not well aligned with the topics and content depth of our courses. We want to test introductory physics content at a level appropriate for our students. Second, we want the assessment to yield scores and gains comparable to the widely used Force Concept Inventory (FCI). After five testing and revision cycles, the assessment was finalized in early 2015 and is available online. We present performance results for a cohort of 225 students at Siena College who were enrolled in our algebra-and calculus-based physics courses during the spring 2015 and 2016 semesters. We provide pretest, post-test, and gain analyses, as well as individual question and whole test statistics to quantify difficulty and reliability. In addition, we compare EMCA and FCI scores and gains, and we find that students' FCI scores are strongly correlated with their performance on the EMCA. Finally, the assessment was piloted in an algebra-based physics course at George Washington University (GWU). We present performance results for a cohort of 130 GWU students and we find that their EMCA scores are comparable to the scores of students in our calculus-based physics course.

Proceedings of the 71st International Symposium on Molecular Spectroscopy, 2016

Ethanimine (CH3CHNH) , including both the E-and Z-isomers, were detected towards the star-forming... more Ethanimine (CH3CHNH) , including both the E-and Z-isomers, were detected towards the star-forming region Sgr B2(N) using the GBT PRIMOS data (Loomis et al 2013), and were recently imaged by the ACTA (Corby et al. 2015). These aldimines can serve as precursors of biological molecules such as amino acids thus are considered prebiotic molecules in interstellar medium. In this study, we present chemical simulations of ethanimine with various physical conditions. From models for Sgr B2(N) and environs, calculated ethanimine abundances show reasonable agreement with observed values, while the translucent cloud models yield much lower abundances. These results agree with locations suggested by observations that ethanimine isomers were detected in the foreground of the shells of the hot core.

Long-chain unsaturated hydrocarbons and cyanopolyynes have recently been observed in the low-mass... more Long-chain unsaturated hydrocarbons and cyanopolyynes have recently been observed in the low-mass star-forming region L1527. a Their unexpected presence was attributed to a gas-phase ion-molecule chemistry, which occurs during and after the evaporation of methane from warming grains. b The source L1527 is an envelope surrounding a Class 0/I low mass protostar with regions that possess a slightly elevated temperature of 30 K. The newly reported molecules are typically associated only with dark molecular clouds, and not with the more evolved hot corino phase. In order to determine if L1527 is chemically distinct from a dark cloud, we compute models including various degrees of heating. These newly observed abundances as well as those of a previous survey c are compared with computed models to determine the quality of agreement. The results indicate that the composition of L1527 is somewhat more likely to be due to "Warm Carbon Chain Chemistry" than to be a remnant of a colder phase. If so, the molecular products provide a signature of a previously uncharacterized early phase of low mass star formation, which can be characterized as a "lukewarm" corino. Although our calculations show that unsaturated hydrocarbons and cyanopolyynes can be produced in the gas phase as the grains warm up to 30 K, they also show that such species do not disappear rapidly from the gas as the temperature reaches 200 K, implying that such species might be detected in hot corinos and hot cores unless their spectral lines cannot be distinguished from the dense spectra of weeds.

The Astrophysical Journal, 2016

The E- and Z-isomers of ethanimine (CH3CHNH) were recently detected toward the star-forming regio... more The E- and Z-isomers of ethanimine (CH3CHNH) were recently detected toward the star-forming region Sagittarius (Sgr) B2(N) using the Green Bank Telescope PRIMOS cm-wave spectral data, and imaged by the Australia Telescope Compact Array. Ethanimine is not reported in the hot cores of Sgr B2, but only in gas that absorbs at +64 and +82 km s−1 in the foreground of continuum emission generated by H ii regions. The ethanimine isomers can serve as precursors of the amino acid alanine and may play important roles in forming biological molecules in the interstellar medium. Here we present a study of the chemistry of ethanimine using a gas-grain simulation based on rate equations, with both isothermal and warm-up conditions. In addition, the density, kinetic temperature, and cosmic ray ionization rate have been varied. For a variety of physical conditions in the warm-up models for Sgr B2(N) and environs, the simulations show reasonable agreement with observationally obtained abundances. Isothermal models of translucent clouds along the same line of sight yield much lower abundances, so that ethanimine would be much more difficult to detect in these sources despite the fact that other complex molecules have been detected there.

Astronomy & Astrophysics, 2016

Ortho-to-para ratio of NH 2 Herschel-HIFI observations of ortho-and para-NH 2 rotational transiti... more Ortho-to-para ratio of NH 2 Herschel-HIFI observations of ortho-and para-NH 2 rotational transitions towards W31C, W49N, W51, and G34.3+0.1

$Research paper thumbnail of CHEMICAL MODELING Of O$_{2}$ IN INTERSTELLAR CLOUDS$

Thesis Rensselaer Polytechnic Institute Source Dai B 65 02 P 788 Aug 2004 113 Pages, Aug 1, 2004

Bulletin of the American Astronomical Society, Dec 1, 2005

Previous models of the low-mass star-forming region L1527 investigated the observations of long-c... more Previous models of the low-mass star-forming region L1527 investigated the observations of long-chain unsaturated hydrocarbon radicals in a gaseous envelope with slightly elevated temperature of ≈ 30 K. These models gradually increased gas and grain temperatures from initially cold (10 K) conditions and demonstrated that the enhanced abundances could be explained by gas-phase ion-molecule chemistry following the evaporation of methane from warming grains. Further, the success of the fit was similar near T ≈ 30 K if the warm-up was truncated at 30 K or allowed to continue upward toward larger temperatures representative of hot core conditions. A secondary conclusion indicated that the hydrocarbon radical species should remain in large abundance as the temperature grows to 200 K. The subsequent implication that these species might be detected in hot corinos and hot cores stands in contrast with the lack of detection toward such sources. As observational interest in low mass star...

Water ice mantles trap more volatile molecules, with an efficiency that depends on the amorphous ... more Water ice mantles trap more volatile molecules, with an efficiency that depends on the amorphous or crystalline structure of the ice. This property will affect the composition of comets forming from the mantles. We find that the processing of mantled grains in protoplanetary disks due to passage through shock waves will determine the crystalline structure. Specifically, the grains suffer a sudden increase in temperature which can evaporate the mantle. This is followed by an extended cooling time during which mantles recondense on timescales comparable to the crystallization time scale. The crystallization of ice and the exclusion of volatiles from the matrix may explain the volatile-depleted composition observed recently in Comet C/1999 S4 (LINEAR). This work was supported by NASA under grant NAG5-7598 to the New York Center for Studies on the Origins of Life.

Astronomy & Astrophysics, 2014

Upper limits to interstellar NH + and para-NH − 2 abundances Herschel-HIFI observations towards S... more Upper limits to interstellar NH + and para-NH − 2 abundances Herschel-HIFI observations towards Sgr B2 (M) and G10.6−0.4 (W31C)

We use a gas-grain chemical network to investigate the initial synthesis of molecular ices as a c... more We use a gas-grain chemical network to investigate the initial synthesis of molecular ices as a cold molecular cloud forms behind a shock in the diffuse interstellar medium. The reaction network includes newly measured rates of photodesorption. The results show that CO is first produced in the gas phase in early stages of cloud birth. This is followed by concurrent

$Research paper thumbnail of A test for the organic refractory model of interstellar dust$

The organic refractory model for interstellar dust postulates that the grains primarily responsib... more The organic refractory model for interstellar dust postulates that the grains primarily responsible for visual extinction consist of silicate cores, coated with organic refractory matter (ORM) that forms by photochemical processing of ice mantles. We use the early-type star Elias 25, in the rho Oph dark cloud, as a test for local production of ORM in an environment where mantled

The water ice mantles on interstellar grains trap volatile molecules, such as CO and CH3OH, with ... more The water ice mantles on interstellar grains trap volatile molecules, such as CO and CH3OH, with an efficiency that depends on the amorphous or crystalline structure of the ice. The ice structure therefore affects the composition of comets formed from the icy grains. We are studying the processing of mantled grains by shock waves in protoplanetary disks. The grains suffer

The Astrophysical Journal, 2008

The low abundance of molecular oxygen in cold cores of interstellar clouds poses a continuing pro... more The low abundance of molecular oxygen in cold cores of interstellar clouds poses a continuing problem to modelers of the chemistry of these regions. In chemical models O 2 is formed principally by the reaction between O and OH, which has been studied experimentally down to 39 K. It remains possible that the rate coefficient of this reaction at 10 K is considerably less than its measured value at 39 K, which might inhibit the production of O 2 and possibly bring theory and observation closer together over a wider range of times. Two theoretical determinations of the rate coefficient for the O þ OH reaction at temperatures down to 10 K have been undertaken recently; both results show that the rate coefficient is indeed lower at 10 K than at 39 K, although they differ in the magnitude of the decrease. Here we show, using gas-phase models, how the calculated interstellar O 2 abundance in cold cores is affected by a decrease in the rate coefficient. We also consider its effect on other species. Our major finding is that for standard O-rich abundances, the calculated abundance of O 2 in cold cores is sufficiently low to explain observations only at early times regardless of the value of k 1 in the range investigated here. For C-rich abundances, on the other hand, late-time solutions can also be possible.

The Astrophysical Journal, 2011

We investigate the formation of molecules during the chemical evolution of a cold dense interstel... more We investigate the formation of molecules during the chemical evolution of a cold dense interstellar cloud using a gas-grain numerical code in order to study the effects of grain-size distribution and grain growth on molecular abundances. Three initial size distributions have been used, based on earlier models. To incorporate different granular sizes, we divided the distribution of sizes utilized into five logarithmically equally spaced ranges, integrated over each range to find its total granular number density, and assigned that number density to an average size in that range. We utilized rate coefficients for surface reactions, accretion, and desorption as functions of grain size. We then followed the chemical evolution of the surface populations of the five average-sized grains along with the gas-phase chemistry. We find that the total effective granular surface area of a distribution is an important parameter in the determination of surface abundances, with and without grain growth. The effect on gas-phase abundances can also be sizable. Grain growth with time increases the rate of depletion of molecules, such as CO, produced in the gas phase. Use of a size distribution for grains in gas-grain models does not improve the agreement of calculated and observed abundances, in the gas or on grains, as compared with models containing "classical" grains of a fixed radius of 0.1 mum. This result helps to verify the quality of the classical grain approximation for cold cloud models. Further, it provides an important basis for future gas-grain models.

$Research paper thumbnail of A Test Case for the Organic Refractory Model of Interstellar Dust$

The Astrophysical Journal, 2003

The organic refractory model of interstellar dust postulates that the grains primarily responsibl... more The organic refractory model of interstellar dust postulates that the grains primarily responsible for visual extinction consist of silicate cores coated with organic refractory matter (ORM) supposed to form by photochemical processing of ice mantles. We identify the line of sight to the early-type star Elias 25, in the Oph dark cloud, as a test for local production of ORM in an environment where mantled grains are exposed to a substantial ultraviolet radiation field. Infrared spectra of Elias 25 in the 2.4-4.0 lm region were used to examine the 3 lm ice profile and to search for the C"H bond absorption feature near 3.4 lm that occurs in laboratory-synthesized ORM. We find that the ice feature in Elias 25 has an unusually deep 3.1-3.7 lm wing, but no detectable 3.4 lm feature is present in the wing profile. An upper limit on the 3:4 =A V ratio is set that is a factor of 4 lower than that determined from the feature detected in the diffuse interstellar medium toward Cygnus OB2 No. 12. Our results are consistent with other evidence indicating that the carrier of the 3.4 lm feature is destroyed, rather than produced, inside dense clouds.