Physics

We developed a microdisplay-based microscope projection photolithography (MDMPP) technique in which a liquid crystal (LC) microdisplay is used as a reconfigurable photomask for a microscope projector. The LC microdisplay provides a significant advantage in terms of cost and speed since patterns can be generated through software instead of redesigning and fabricating glass photomasks. The constructed MDMPP system could produce line patterns as narrow as 2.4 um, smaller than that specified by the diffraction limit, with the aid of a 4X objective lens. The achievement of a linewidth smaller than the theoretical limit may be ascribed to a combination of overexposure and the underetching effect, in addition to the good optical performance of the system. In a diffraction experiment performed with fabricated slits, the application of the MDMPP technique helped provide various patterns of the slits, demonstrating the potential usefulness of the MDMPP system in undergraduate optics courses. We expect that MDMPP can contribute to the field of physics education and various areas of research, such as chemistry and biology, in the future.

Measuring the coefficient of kinetic friction is much more difficult than that of the static counterpart. Here we report a simple method using minimal tool to accurately measuring the coefficient of kinetic friction. We employed an inclined plane, the tool for measuring time, and a protractor. This method is much simpler and cheaper than other methods reported by some authors previously. The results are consistent with the date reported elsewhere.

Since its serendipitous discovery in 1896 by Henry Becquerel, radioactivity has called the attention of both the scientific community and the broad audience due to its intriguing nature, its multiple applications and its controversial uses. For this reason, the teaching of the phenomenon is considered a key ingredient in the path towards developing critical-thinking skills in many secondary science education curricula. Despite being one of the basic concepts in general physics courses, the scientific teaching literature of the last 40 years reports a great deal of misconceptions and conceptual errors related to radioactivity that seemingly appear regardless of the context. This study explores, for the first time, the knowledge status on the topic on a sample of N=191 secondary school students and Y=29 Physics-and-Chemistry trainee teachers in the Spanish region of Valencia. To this aim, a revised version of a diagnostic tool developed by Martins \cite{Mar92} has been employed. In general, the results reveal an evolution from a widespread dissenting notion on the phenomenon, which is staunchly related to danger, hazard and destruction in the lowest educational levels, towards a more rational, relative and multidimensional perspective in the highest ones. Furthermore, the great overlap of the ideas, emotions and attitudes of the inquired individuals with the main misconceptions and conceptual mistakes reported in the literature for different educational contexts unveils the urgent need to develop new teaching strategies leading to a meaningful learning of the associated nuclear science concepts.

Physics education researchers (PER) commonly use complete-case analysis to address missing data. For complete-case analysis, researchers discard all data from any student who is missing any data. Despite its frequent use, no PER article we reviewed that used complete-case analysis provided evidence that the data met the assumption of missing completely at random (MCAR) necessary to ensure accurate results. Not meeting this assumption raises the possibility that prior studies have reported biased results with inflated gains that may obscure differences across courses. To test this possibility, we compared the accuracy of complete-case analysis and multiple imputation (MI) using simulated data. We simulated the data based on prior studies such that students who earned higher grades participated at higher rates, which made the data missing at random (MAR). PER studies seldom use MI, but MI uses all available data, has less stringent assumptions, and is more accurate and more statistically powerful than complete-case analysis. Results indicated that complete-case analysis introduced more bias than MI and this bias was large enough to obscure differences between student populations or between courses. We recommend that the PER community adopt the use of MI for handling missing data to improve the accuracy in research studies.

We describe a simple method to experimentally determine the frequency dependencies of the per-unit-length resistance and conductance of transmission lines. The experiment is intended as a supplement to the classic measurement of the transient response of a transmission line to a voltage step or pulse. In the transient experiment, an ideal (lossless) model of the transmission line is used to determine the characteristic impedance and signal propagation speed. In our experiment, the insertion losses of various coaxial cables are measured as a function of frequency from 1 to 2000 MHz. A full distributed circuit model of the transmission line that includes both conductor and dielectric losses is needed to fit the frequency dependence of the measured insertion losses. Our model assumes physically-sensible frequency dependencies for the per-unit-length resistance and conductance that are determined by the geometry of the coaxial transmission lines used in the measurements.

We adopted survival analysis for the viewing durations of massive open online courses. The hazard function of empirical duration data is dominated by a bathtub curve and has the Lindy effect in its tail. To understand the evolutionary mechanisms underlying these features, we categorized learners into two classes due to their different distributions of viewing durations, namely lognormal distribution and power law with exponential cutoff. Two random differential equations are provided to describe the growth patterns of viewing durations for the two classes respectively. The expected duration change rate of the learners featured by lognormal distribution is supposed to be dependent on their past duration, and that of the rest learners is supposed to be inversely proportional to time. Solutions to the equations predict the features of viewing duration distributions, and those of the hazard function. The equations also reveal the feature of memory and that of memorylessness for the viewing behaviors of the two classes respectively.

A self-training scheme geared at inducing students to improve their skills through independent homework is presented. The motivation is to identify an inexpensive, yet effective tool for raising the competence level of students in the Fundamental Sciences (in particular Physics). Since globally existing financial restrictions do not allow for extensive supervised work, a scheme is devised where the additional personal training is rewarded through bonuses in the grade, while safeguarding against the danger of cheating. Overburdening the instructors is avoided through the use of computer-based grading of homework, while a carefully chosen bonus plan, weighted by the grades obtained in supervised tests, counters the effects of potential cheating.

Problem solving in physics and mathematics have been characterized in terms of five phases by Schonfeld and these have previously been used to describe also online and blended behavior. We argue that expanding the use of server logs to make detailed categorizations of student actions can help increase knowledge about how students solve problems. We present a novel approach for analyzing server logs that relies on network analysis and principal component analysis. We use the approach to analyze student interactions with an online textbook that features physics problems. We find five 'components of behavioral structure': Complexity, Linear Length, Navigation, Mutuality, and Erraticism. Further, we find that problem solving sessions can be divided into three over-arching groups that differ in their Complexity and further into ten clusters that also differ on the other components. Analyzing typical sessions in each cluster, we find ten different behavioral structures,which we describe in terms of Schonfeld's phases. We suggest that further research integrates this approach with other methodological approaches to get a fuller picture of how learning strategies are employed by students in settings with online features.

This study uses positional analysis to describe the student interaction networks in four research-based introductory physics curricula. Positional analysis is a technique for simplifying the structure of a network into blocks of actors whose connections are more similar to each other than to the rest of the network. This method describes social structure in a way that is comparable between networks of different sizes and densities and can show large-scale patterns such as hierarchy or brokering among actors. We detail the method and apply it to class sections using Peer Instruction, SCALE-UP, ISLE, and context-rich problems. At the level of detail shown in the blockmodels, most of the curricula are more alike than different, showing a late-term tendency to form coherent subgroups that communicate actively among themselves but have few inter-position links. This pattern may be a network signature of active learning classes, but wider data collection is needed to investigate.

International Masterclasses (IMC) have developed since their introduction in 2005. Masterclasses for International Day of Women and Girls in Science (IDWGS) and World Wide Data Day (W2D2) are innovations that began two years ago and are going well. With IDWGS masterclasses, a new pathway has been opened for high school girls to be encouraged in physics. W2D2 establishes new ways to bring masterclass activities directly to high school classrooms. New masterclass measurements beyond those for the LHC have been developed and tested, notably the MINERvA neutrino masterclass, which is the first IMC offering in neutrino physics and the first based on a Fermilab experiment. In the MINERvA measurement, students are able to study interactions of a neutrino beam with carbon nuclei, using conservation of momentum to draw conclusions. Other masterclass measurements related to Belle II and medical imaging are also in the testing stage. More neutrino masterclasses are in development as well, especially for MicroBooNE. A longer-term goal is the creation of a DUNE masterclass measurement as that facility reaches the data-taking stage.