chandralekha singh | University of Pittsburgh (original) (raw)
Papers by chandralekha singh
2019 Physics Education Research Conference Proceedings, 2020
An earlier study using sequences of online learning modules found that a significant fraction of ... more An earlier study using sequences of online learning modules found that a significant fraction of undergraduate students were unable to solve similar new problems after learning from an online problem solving tutorial. The current study examines the effectiveness of two methods to improve students' subsequent problem solving performance. First, an "on-ramp" module designed to help students develop proficiency in relevant basic skills was added prior to the tutorial. We found that students' performance on subsequent modules improved significantly over the previous year, and in one of the two sequences we found evidence to support that the improvement was due to the addition of the on-ramp module rather than other irrelevant factors. Second, a new "transfer" module was added after the tutorial and before the final quiz module in which half of the students were given a comparecontrast task and the other half were asked to answer tutorial-style scaffolding questions. On the subsequent quiz module, we did not find significant performance differences between the two conditions, nor did students' performance significantly improve over the previous year. The study demonstrated that mastery-style online homework can serve as an efficient and flexible method for evaluating the effectiveness of new instructional designs.
Physical Review Physics Education Research, 2018
Several prior studies in introductory physics have found a gender gap, i.e., a difference between... more Several prior studies in introductory physics have found a gender gap, i.e., a difference between male and female students' performance on conceptual assessments such as the Force Concept Inventory (FCI) and the Conceptual Survey of Electricity and Magnetism (CSEM) with male students performing better than female students. Moreover, prior studies in the context of mathematics have also found that activation of a negative stereotype about a group or stereotype threat, e.g., asking test takers to indicate their ethnicity before taking a test, can lead to deteriorated performance of the stereotyped group. Here, we describe two studies in which we investigated the impact of interventions on the gender gap on the FCI and CSEM in large (more than 100 students) introductory physics courses at a large research university. In the first study, we investigated whether asking introductory physics students to indicate their gender immediately before taking the CSEM increased the gender gap compared to students who were not asked for this information. We found no difference in performance between male and female students in the two conditions. In the second study, which was conducted with several thousand introductory physics students, we investigated the prevalence of the belief that men generally perform better in physics than women and the extent to which this belief is correlated with the performance of both female and male students on the FCI and the CSEM in algebra-based and calculus-based physics courses. We found that at the end of the year-long calculus-based introductory physics sequence, in which female students are significantly underrepresented, agreeing with a gender stereotype was correlated negatively with the performance of female students on the conceptual physics surveys. The fact that female students who agreed with the gender stereotype performed worse than female students who disagreed with it at the end of the year-long calculus-based physics course may partly be due to an increased stereotype threat that female students who agree with the stereotype may experience in this course in which they are severely underrepresented.
MRS Proceedings, 1996
ABSTRACTUsing a two dimensional self-consistent field theory, we investigate the interactions bet... more ABSTRACTUsing a two dimensional self-consistent field theory, we investigate the interactions between two planar surfaces that are coated with terminally-anchored homopolymers. One surface is coated with A chains and the other is covered with B homopolymers. The chains are grafted at low densities and the B polymers are chosen to be solvophobic, while the A chains are relatively solvophilic. We determine the morphology of the layers and the energy of interaction asthe surfaces are compressed. Our results provide guidelines for controlling the interaction between polymer-coated colloidal particles.
Aps March Meeting Abstracts, Mar 1, 1997
The Journal of Physical Chemistry B, 1997
Using a two-dimensional self-consistent field calculation and scaling theory, we investigate the ... more Using a two-dimensional self-consistent field calculation and scaling theory, we investigate the interaction between two planar surfaces where: (1) each surface is grafted with both solvophilic and solvophobic homopolymers and (2) both surfaces are coated with solvophobic polyelectrolytes. The chains are tethered by one end and grafted at relatively low densities. For both systems, we determine the morphology of the layers and the energy of interaction as the layers are compressed. The energy of interaction versus distance profiles show a wide region of attraction as the surfaces are brought together. This attractive interaction is due to the self-assembled structures that appear at low grafting densities in poor solvents. Furthermore, for polyelectrolytes at high degrees of ionization (R), compressing the layers results in a novel first-order phase transition: the uniformly stretched, charged chains spontaneously associate into aggregates (pinned micelles) on the surfaces. At both low and high R, the free energy versus distance profiles reveal distinct minima, which indicate an optimal separation between the surfaces. Our findings provide guidelines for controlling the interactions between coated colloidal particles and yield design criteria for driving colloids to self-assemble into ordered arrays.
Progress in Surface Science, 1997
Using self-consistent field calculations and scaling analysis, we determined the property of poly... more Using self-consistent field calculations and scaling analysis, we determined the property of polymers that are tethered onto impenetrable, solid surfaces or adsorbed onto penetrable interfaces. In the case of impenetrable solids, we consider homogeneous walls, as well as surfaces containing chemically distinct patterns. These findings provide guidelines for tailoring the morphology of the polymer layer and thereby controling the interaction
Polymer International, 2000
... Research Article. Effect of polymer architecture on the miscibility of polymer/clay mixtures.... more ... Research Article. Effect of polymer architecture on the miscibility of polymer/clay mixtures.Chandralekha Singh,; Anna C Balazs. Article first published online: 13 JUL 2000. ... Funded by. Army Office of Research; ONR. Grant Number: N00014-91-J-1363. SEARCH. ...
Macromolecules, 2000
ABSTRACT
Macromolecules, 1996
... Ekaterina B. Zhulina, Chandralekha Singh, and Anna ... The parameter n i , c (r) is the... more ... Ekaterina B. Zhulina, Chandralekha Singh, and Anna ... The parameter n i , c (r) is the number density at r of molecules of type i in conformation c. In the enthalpic term, the indices j and k run over all the different types of segments and φ j (r) represents the average density of ...
Macromolecules, 1998
ABSTRACT We use scaling theory and two-dimensional self-consistent field calculations to investig... more ABSTRACT We use scaling theory and two-dimensional self-consistent field calculations to investigate the adsorption of copolymers onto heterogeneous surfaces, which represent the surface of the influenza virus. The copolymers contain “stickers” that are highly attracted to receptors on the viral surface. We vary the sticker concentration and determine the conformation of the adsorbed chains on the heterogeneous substrate. We then calculate the interaction energy as a function of distance between this polymer-coated surface and a bare interface, which represents the surface of a red blood cell. The results show that there is an optimal range of the sticker concentrations that sterically inhibit contact between the two surfaces. The findings help rationalize recent experiments, which show that the extent of inhibition depends on the fraction of stickers in adsorbing copolymer.
Macromolecules, 1996
Using a two-dimensional self-consistent field theory, we investigate the interaction between two ... more Using a two-dimensional self-consistent field theory, we investigate the interaction between two planar surfaces where (1) each surface is grafted with both A and B homopolymers and (2) one surface is coated with end-grafted A's and the other is coated with end-grafted B's. The chains are grafted at low densities and the B polymers are chosen to be solvophobic. We vary the solvent affinity of the A chains and the interaction between the A and B monomers. We determine the morphology of the layers and the energy of interaction as the layers are compressed. The energy of interaction versus distance profiles show a wide region of attraction as the surfaces are brought together. This attractive interaction is due to the self-assembled structures that appear at low grafting densities in poor solvents. The properties of the attraction can be tailored, as we demonstrate in a simple scaling picture. Our findings indicate that fine control over the pair interaction function of coated colloidal particles can be gained through grafting mixtures of homopolymers.
Langmuir, 1999
Using numerical and analytical self-consistent field (SCF) calculations, we investigate the inter... more Using numerical and analytical self-consistent field (SCF) calculations, we investigate the interactions between two closely spaced surfaces and the surrounding polymer melt, which contains a volume fraction of end-functionalized polymers. The functionalized polymers contain two reactive "stickers", one at each end of the chain, that are highly attracted to the surfaces. The surfaces model clay crystallites, or sheets. Through the calculations, we determine the free energy profiles as the surfaces are pried apart and the polymer fills the gap. The free energy vs distance plots reveal a distinctive minimum, even at very small volume fractions of the end-functionalized chains. Thus, the presence of these telechelic polymers promotes the formation of thermodynamically stable intercalated composites, where the polymers enhance the separation between the silicate sheets. However, the telechelic chains prohibit the creation of the more desirable exfoliated structures, where the sheets are uniformly dispersed throughout the polymer matrix. The results provide guidelines for significantly enhancing the separation between the sheets, thus possibly making properties of the intercalated composites more like the exfoliated material.
The Journal of Chemical Physics, 1998
ABSTRACT Using scaling theory and a two-dimensional self-consistent field calculation (SCF), we d... more ABSTRACT Using scaling theory and a two-dimensional self-consistent field calculation (SCF), we determine the morphology and phase behavior of charged polymers tethered by one end onto a flat substrate, and immersed in a poor solvent. For degrees of ionization, alpha, below a critical value, alpha*, the effects of the poor solvent dominate and the tethered chains collapse into pinned micelles on the planar surface. For values of alpha>alpha*, the chains extend to form a laterally uniform layer. This collapsed-to-stretched transformation constitutes a first-order phase transition. The specific routes to this transition are dependent on the relative solvent quality, and are described via the scaling theory. The structure of the layers above and below alpha* can be visualized through the polymer density profiles, which are obtained from the SCF calculations. The SCF calculations also show agreement with predictions from the scaling analysis.
Accounts of Chemical Research, 1999
Physical Review Physics Education Research
Creating equitable learning environments has been an area of significant focus for physics educat... more Creating equitable learning environments has been an area of significant focus for physics education researchers in recent years. Here we introduce a framework that posits that grade penalty is a measure of academic self-concept and investigate if there are gender differences in grade penalties in physics courses for students majoring in physics. In order to quantify grade penalty, we define grade anomaly as the difference between a student's grade in a course under consideration and their grade point average (GPA) in all other classes thus far. A grade anomaly lower than students expected grade based on their GPA is a grade penalty and higher than expected average grade is a grade bonus. Our framework posits that since women have traditionally been marginalized in physics, female physics majors are more likely to be negatively impacted by a grade penalty in their courses since their academic self-concept as a physics major hinges on them securing a certain grade. In the study presented here, we examine the average grade anomalies across a number of courses for female and male physics majors. We find that these students received grade penalties in almost all physics courses studied, though there were grade bonuses in a few laboratory courses. We also find that in physics courses, on average, women often had larger grade penalties than men, especially in introductory courses. We hypothesize that, because their grade penalties are often larger than men's, women's decisions to pursue a physics major and career may be particularly affected by grade penalties received in their various courses. Furthermore, the grade penalty measure can be easily computed by the physics programs concerned with equity.
arXiv (Cornell University), Feb 22, 2016
being certain to turn off your signature before sending: SUBSCRIBE jpteo-l. When issues are publi... more being certain to turn off your signature before sending: SUBSCRIBE jpteo-l. When issues are published online, subscribers will receive electronic notification of availability. JPTEO is published on an irregular basis, but with an expectation of four issues per calendar year. JPTEO is available free of charge through the JPTEO website. It is downloadable in portable document file (PDF) format. All contents of this publication are copyrighted by the Illinois State University Department of Physics. REVIEWERS The following individuals have graciously agreed to serve as reviewers for this publication. This publication would not be possible without their assistance.
KYLEM. WHITCOMB, Z. YASEMIN KALENDER, TIMOTHY J. NOKES-MALACH, CHRISTIAN D. SCHUNN and CHANDRALEK... more KYLEM. WHITCOMB, Z. YASEMIN KALENDER, TIMOTHY J. NOKES-MALACH, CHRISTIAN D. SCHUNN and CHANDRALEKHA SINGH Department of Physics and Astronomy, University of Pittsburgh, Allen Hall, 3941 O’Hara St, Pittsburgh, PA 15260, USA. E-mail: kmw136@pitt.edu, zyk2@pitt.edu, clsingh@pitt.edu Learning Research and Development Center, University of Pittsburgh, LRDC, 3939 O’Hara St, Pittsburgh, PA 15260, USA. E-mail: nokes@pitt.edu, schunn@pitt.edu
2019 Physics Education Research Conference Proceedings, 2020
An earlier study using sequences of online learning modules found that a significant fraction of ... more An earlier study using sequences of online learning modules found that a significant fraction of undergraduate students were unable to solve similar new problems after learning from an online problem solving tutorial. The current study examines the effectiveness of two methods to improve students' subsequent problem solving performance. First, an "on-ramp" module designed to help students develop proficiency in relevant basic skills was added prior to the tutorial. We found that students' performance on subsequent modules improved significantly over the previous year, and in one of the two sequences we found evidence to support that the improvement was due to the addition of the on-ramp module rather than other irrelevant factors. Second, a new "transfer" module was added after the tutorial and before the final quiz module in which half of the students were given a comparecontrast task and the other half were asked to answer tutorial-style scaffolding questions. On the subsequent quiz module, we did not find significant performance differences between the two conditions, nor did students' performance significantly improve over the previous year. The study demonstrated that mastery-style online homework can serve as an efficient and flexible method for evaluating the effectiveness of new instructional designs.
Physical Review Physics Education Research, 2018
Several prior studies in introductory physics have found a gender gap, i.e., a difference between... more Several prior studies in introductory physics have found a gender gap, i.e., a difference between male and female students' performance on conceptual assessments such as the Force Concept Inventory (FCI) and the Conceptual Survey of Electricity and Magnetism (CSEM) with male students performing better than female students. Moreover, prior studies in the context of mathematics have also found that activation of a negative stereotype about a group or stereotype threat, e.g., asking test takers to indicate their ethnicity before taking a test, can lead to deteriorated performance of the stereotyped group. Here, we describe two studies in which we investigated the impact of interventions on the gender gap on the FCI and CSEM in large (more than 100 students) introductory physics courses at a large research university. In the first study, we investigated whether asking introductory physics students to indicate their gender immediately before taking the CSEM increased the gender gap compared to students who were not asked for this information. We found no difference in performance between male and female students in the two conditions. In the second study, which was conducted with several thousand introductory physics students, we investigated the prevalence of the belief that men generally perform better in physics than women and the extent to which this belief is correlated with the performance of both female and male students on the FCI and the CSEM in algebra-based and calculus-based physics courses. We found that at the end of the year-long calculus-based introductory physics sequence, in which female students are significantly underrepresented, agreeing with a gender stereotype was correlated negatively with the performance of female students on the conceptual physics surveys. The fact that female students who agreed with the gender stereotype performed worse than female students who disagreed with it at the end of the year-long calculus-based physics course may partly be due to an increased stereotype threat that female students who agree with the stereotype may experience in this course in which they are severely underrepresented.
MRS Proceedings, 1996
ABSTRACTUsing a two dimensional self-consistent field theory, we investigate the interactions bet... more ABSTRACTUsing a two dimensional self-consistent field theory, we investigate the interactions between two planar surfaces that are coated with terminally-anchored homopolymers. One surface is coated with A chains and the other is covered with B homopolymers. The chains are grafted at low densities and the B polymers are chosen to be solvophobic, while the A chains are relatively solvophilic. We determine the morphology of the layers and the energy of interaction asthe surfaces are compressed. Our results provide guidelines for controlling the interaction between polymer-coated colloidal particles.
Aps March Meeting Abstracts, Mar 1, 1997
The Journal of Physical Chemistry B, 1997
Using a two-dimensional self-consistent field calculation and scaling theory, we investigate the ... more Using a two-dimensional self-consistent field calculation and scaling theory, we investigate the interaction between two planar surfaces where: (1) each surface is grafted with both solvophilic and solvophobic homopolymers and (2) both surfaces are coated with solvophobic polyelectrolytes. The chains are tethered by one end and grafted at relatively low densities. For both systems, we determine the morphology of the layers and the energy of interaction as the layers are compressed. The energy of interaction versus distance profiles show a wide region of attraction as the surfaces are brought together. This attractive interaction is due to the self-assembled structures that appear at low grafting densities in poor solvents. Furthermore, for polyelectrolytes at high degrees of ionization (R), compressing the layers results in a novel first-order phase transition: the uniformly stretched, charged chains spontaneously associate into aggregates (pinned micelles) on the surfaces. At both low and high R, the free energy versus distance profiles reveal distinct minima, which indicate an optimal separation between the surfaces. Our findings provide guidelines for controlling the interactions between coated colloidal particles and yield design criteria for driving colloids to self-assemble into ordered arrays.
Progress in Surface Science, 1997
Using self-consistent field calculations and scaling analysis, we determined the property of poly... more Using self-consistent field calculations and scaling analysis, we determined the property of polymers that are tethered onto impenetrable, solid surfaces or adsorbed onto penetrable interfaces. In the case of impenetrable solids, we consider homogeneous walls, as well as surfaces containing chemically distinct patterns. These findings provide guidelines for tailoring the morphology of the polymer layer and thereby controling the interaction
Polymer International, 2000
... Research Article. Effect of polymer architecture on the miscibility of polymer/clay mixtures.... more ... Research Article. Effect of polymer architecture on the miscibility of polymer/clay mixtures.Chandralekha Singh,; Anna C Balazs. Article first published online: 13 JUL 2000. ... Funded by. Army Office of Research; ONR. Grant Number: N00014-91-J-1363. SEARCH. ...
Macromolecules, 2000
ABSTRACT
Macromolecules, 1996
... Ekaterina B. Zhulina, Chandralekha Singh, and Anna ... The parameter n i , c (r) is the... more ... Ekaterina B. Zhulina, Chandralekha Singh, and Anna ... The parameter n i , c (r) is the number density at r of molecules of type i in conformation c. In the enthalpic term, the indices j and k run over all the different types of segments and φ j (r) represents the average density of ...
Macromolecules, 1998
ABSTRACT We use scaling theory and two-dimensional self-consistent field calculations to investig... more ABSTRACT We use scaling theory and two-dimensional self-consistent field calculations to investigate the adsorption of copolymers onto heterogeneous surfaces, which represent the surface of the influenza virus. The copolymers contain “stickers” that are highly attracted to receptors on the viral surface. We vary the sticker concentration and determine the conformation of the adsorbed chains on the heterogeneous substrate. We then calculate the interaction energy as a function of distance between this polymer-coated surface and a bare interface, which represents the surface of a red blood cell. The results show that there is an optimal range of the sticker concentrations that sterically inhibit contact between the two surfaces. The findings help rationalize recent experiments, which show that the extent of inhibition depends on the fraction of stickers in adsorbing copolymer.
Macromolecules, 1996
Using a two-dimensional self-consistent field theory, we investigate the interaction between two ... more Using a two-dimensional self-consistent field theory, we investigate the interaction between two planar surfaces where (1) each surface is grafted with both A and B homopolymers and (2) one surface is coated with end-grafted A's and the other is coated with end-grafted B's. The chains are grafted at low densities and the B polymers are chosen to be solvophobic. We vary the solvent affinity of the A chains and the interaction between the A and B monomers. We determine the morphology of the layers and the energy of interaction as the layers are compressed. The energy of interaction versus distance profiles show a wide region of attraction as the surfaces are brought together. This attractive interaction is due to the self-assembled structures that appear at low grafting densities in poor solvents. The properties of the attraction can be tailored, as we demonstrate in a simple scaling picture. Our findings indicate that fine control over the pair interaction function of coated colloidal particles can be gained through grafting mixtures of homopolymers.
Langmuir, 1999
Using numerical and analytical self-consistent field (SCF) calculations, we investigate the inter... more Using numerical and analytical self-consistent field (SCF) calculations, we investigate the interactions between two closely spaced surfaces and the surrounding polymer melt, which contains a volume fraction of end-functionalized polymers. The functionalized polymers contain two reactive "stickers", one at each end of the chain, that are highly attracted to the surfaces. The surfaces model clay crystallites, or sheets. Through the calculations, we determine the free energy profiles as the surfaces are pried apart and the polymer fills the gap. The free energy vs distance plots reveal a distinctive minimum, even at very small volume fractions of the end-functionalized chains. Thus, the presence of these telechelic polymers promotes the formation of thermodynamically stable intercalated composites, where the polymers enhance the separation between the silicate sheets. However, the telechelic chains prohibit the creation of the more desirable exfoliated structures, where the sheets are uniformly dispersed throughout the polymer matrix. The results provide guidelines for significantly enhancing the separation between the sheets, thus possibly making properties of the intercalated composites more like the exfoliated material.
The Journal of Chemical Physics, 1998
ABSTRACT Using scaling theory and a two-dimensional self-consistent field calculation (SCF), we d... more ABSTRACT Using scaling theory and a two-dimensional self-consistent field calculation (SCF), we determine the morphology and phase behavior of charged polymers tethered by one end onto a flat substrate, and immersed in a poor solvent. For degrees of ionization, alpha, below a critical value, alpha*, the effects of the poor solvent dominate and the tethered chains collapse into pinned micelles on the planar surface. For values of alpha>alpha*, the chains extend to form a laterally uniform layer. This collapsed-to-stretched transformation constitutes a first-order phase transition. The specific routes to this transition are dependent on the relative solvent quality, and are described via the scaling theory. The structure of the layers above and below alpha* can be visualized through the polymer density profiles, which are obtained from the SCF calculations. The SCF calculations also show agreement with predictions from the scaling analysis.
Accounts of Chemical Research, 1999
Physical Review Physics Education Research
Creating equitable learning environments has been an area of significant focus for physics educat... more Creating equitable learning environments has been an area of significant focus for physics education researchers in recent years. Here we introduce a framework that posits that grade penalty is a measure of academic self-concept and investigate if there are gender differences in grade penalties in physics courses for students majoring in physics. In order to quantify grade penalty, we define grade anomaly as the difference between a student's grade in a course under consideration and their grade point average (GPA) in all other classes thus far. A grade anomaly lower than students expected grade based on their GPA is a grade penalty and higher than expected average grade is a grade bonus. Our framework posits that since women have traditionally been marginalized in physics, female physics majors are more likely to be negatively impacted by a grade penalty in their courses since their academic self-concept as a physics major hinges on them securing a certain grade. In the study presented here, we examine the average grade anomalies across a number of courses for female and male physics majors. We find that these students received grade penalties in almost all physics courses studied, though there were grade bonuses in a few laboratory courses. We also find that in physics courses, on average, women often had larger grade penalties than men, especially in introductory courses. We hypothesize that, because their grade penalties are often larger than men's, women's decisions to pursue a physics major and career may be particularly affected by grade penalties received in their various courses. Furthermore, the grade penalty measure can be easily computed by the physics programs concerned with equity.
arXiv (Cornell University), Feb 22, 2016
being certain to turn off your signature before sending: SUBSCRIBE jpteo-l. When issues are publi... more being certain to turn off your signature before sending: SUBSCRIBE jpteo-l. When issues are published online, subscribers will receive electronic notification of availability. JPTEO is published on an irregular basis, but with an expectation of four issues per calendar year. JPTEO is available free of charge through the JPTEO website. It is downloadable in portable document file (PDF) format. All contents of this publication are copyrighted by the Illinois State University Department of Physics. REVIEWERS The following individuals have graciously agreed to serve as reviewers for this publication. This publication would not be possible without their assistance.
KYLEM. WHITCOMB, Z. YASEMIN KALENDER, TIMOTHY J. NOKES-MALACH, CHRISTIAN D. SCHUNN and CHANDRALEK... more KYLEM. WHITCOMB, Z. YASEMIN KALENDER, TIMOTHY J. NOKES-MALACH, CHRISTIAN D. SCHUNN and CHANDRALEKHA SINGH Department of Physics and Astronomy, University of Pittsburgh, Allen Hall, 3941 O’Hara St, Pittsburgh, PA 15260, USA. E-mail: kmw136@pitt.edu, zyk2@pitt.edu, clsingh@pitt.edu Learning Research and Development Center, University of Pittsburgh, LRDC, 3939 O’Hara St, Pittsburgh, PA 15260, USA. E-mail: nokes@pitt.edu, schunn@pitt.edu