John W Belcher

Massachusetts Institute of Technology (MIT), Physics, Emeritus

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Address: Room 587 Building 37
Massachusetts Institute of Technology
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Papers by John W Belcher

Voyager Plasma Science Instrument

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Alfvén Waves in the Interplanetary Medium

A study of the wave properties of the microscale fluctuations (scale lengths of .01 a.u. and less... more A study of the wave properties of the microscale fluctuations (scale lengths of .01 a.u. and less) in the interplanetary medium is presented using plasma and magnetic field data from Mariner V (Venus 1967). The reduction procedure for the magnetic field data is summarized, and descriptions are given of the MIT plasma data and the merged plasma/field data tapes used in the analysis. Observationally, it is found that large amplitude, nonsinusoidal Alfven waves propagating outward from the sun with a broad wavelength range from 103 to 5 x 106km dominate the microscale structure at least 50% of the time. The waves frequently have an energy density comparable both to the unperturbed magnetic field energy density and to the thermal energy density. The purest examples of the Alfven waves are found in high velocity solar wind streams and on their trailing edges. The largest amplitude waves occur in the compression regions at the leading edges of high velocity streams where the velocity incr...

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Large-amplitude Alfvén waves in the interplanetary medium: Mariner 5

Journal of Geophysical Research, 1969

Correlation coefficients greater than 0.8 in absolute value between the radial components of the ... more Correlation coefficients greater than 0.8 in absolute value between the radial components of the interplanetary magnetic field and the solar wind velocity are found at least 30% of the time in five months of data from Mariner 5 (Venus 1967). They can best be explained as due to large-amplitu.de, aperiodic AlfvSn waves propagating outward from the sun along the average magnetic field direction. The magnetic fluctuations on such occasions are predominantly normal to the average field direction, have characteristic times of the general order of one hour, and the fluctuations in density are relatively small. ful to Drs. H. S. Bridge and A. J. Lazarus for supplying extensive and detailed data from the Mariner 5 plasma probe experiment, to I)rs. P. J. Coleman, Jr., and D. E. Jones, our co-experimenters on the magnetometer experiment, for the use of the magnetometer data, and to all of these Mariner experimenters for stimulating discussions.

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Comparison of electromagnetic and gravitational radiation: What we can learn about each from the other

American Journal of Physics, 2013

We compare the nature of electromagnetic fields and gravitational fields in linearized general re... more We compare the nature of electromagnetic fields and gravitational fields in linearized general relativity. We carry out this comparison both mathematically and visually. In particular, the “lines of force” visualizations of electromagnetism are contrasted with the recently introduced tendex/vortex eigenline technique for visualizing gravitational fields. Specific solutions, visualizations, and comparisons are given for an oscillating point quadrupole source. Among the similarities illustrated are the quasistatic nature of the near fields, the transverse 1/r nature of the far fields, and the interesting intermediate field structures connecting these two limiting forms. Among the differences illustrated are the meaning of field line motion and of the flow of energy.

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ElectroVR: An Electrostatic Playground for Collaborative, Simulation-Based Exploratory Learning in Immersive Virtual Reality

Computer Supported Collaborative Learning, Jun 1, 2019

The ElectroVR interactive demonstration allows two participants to occupy a single physical and i... more The ElectroVR interactive demonstration allows two participants to occupy a single physical and immersive virtual space with one another, in which they can learn through spatial interaction with an electrostatics simulation sandbox. Narrative sequences optionally offer exposition of key principles and suggestions of exploratory activities. The demo shows three key approaches operating in tandem: collocated, multiuser , positionally tracked Virtual Reality (VR); a spatial simulation-based exploratory learning environment; and a playback system that presents narrative sequences prepared by instructors in the virtual environment. As such, it offers a novel and powerful embodiment of the "4E learning" paradigm that is the theme of this conference.

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Magnetic holes are isolated intervals of depleted interplanetary magnetic field (IMF) strength on... more Magnetic holes are isolated intervals of depleted interplanetary magnetic field (IMF) strength on timescales of several seconds to several hours. These intervals have been seen as often as several times per day in the ecliptic and at high heliospheric latitudes from 1 AU to 5.4 AU. We present a scale-free statistical technique for identifying magnetic holes and evaluating their significance relative to turbulent fluctuations in the solar wind. We apply this technique in a comprehensive search for magnetic holes in the Wind and ACE magnetometer data streams through 2004. Using magnetic field and ion measurements on the Wind spacecraft, we present the first statistical study of magnetic hole plasma signatures on the kinetic scale and we present a comparison of magnetic holes as kinetic and microscale phenomena. Magnetic holes are shown to be pressure-balanced structures with similar properties on all scales. Temperature anisotropy measurements are combined with magnetic field measurements to give direct evidence that the mirror-mode instability in the solar wind is a likely source of magnetic holes. Two-satellite correlations between ACE and Wind indicate that magnetic holes are stationary with respect to the solar wind and elongated along the IMF.

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Improving Students’ Understanding of Electromagnetic Principles with an Alternator Design-Build-Test Project

2019 ASEE Annual Conference & Exposition Proceedings

Science educators face a challenge of developing and implementing technology-rich learning materi... more Science educators face a challenge of developing and implementing technology-rich learning materials and environments, especially in higher education. The Technology-Enabled Active Learning (TEAL) Project at MIT involves media-rich software for simulation and visualization in freshman physics. The objective of the project is to transform the way physics is taught in large enrollment physics classes at MIT in order to increase students' conceptual and analytical understanding and decrease failure rates in these courses. The approach is designed to help students develop better intuition about, and conceptual models of, electromagnetic phenomena. The reform is centered on an "active learning" approach-a collaborative, hands-on environment, with the use of desktop experiments, visualizations, web-based assignments, and a personal response system. The objective of the research is to assess cognitive outcomes of MIT undergraduate students who study electromagnetism in a large-scale TEAL setting and compare them with outcomes obtained in small-scale TEAL and traditional settings. We compared three groups: small-scale TEAL implementation, large-scale TEAL implementation, and traditional setting. Our study establishes that the TEAL-studio format has a significant and strong positive effect on the learning outcomes of MIT freshmen. The TEAL format enhanced the students' ability to transfer electromagnetic concepts from abstract to concrete.

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The MIT TEAL Simulations and Visualizations in Electromagnetism

Aps March Meeting Abstracts, Mar 1, 2007

Learning (TEAL) Project at MIT has developed a broad range of 3D visualizations and simulations t... more Learning (TEAL) Project at MIT has developed a broad range of 3D visualizations and simulations to foster student intuition about electromagnetic fields and phenomena (see http://web.mit.edu/8.02t/www/802TEAL3D/). In this talk we discuss the software approaches we use to create these simulations, including Macromedia Shockwave and Java 3D applets for interactive visualization, passive animations created with 3ds max, and the Dynamic Line Integral Convolution (DLIC) method for constructing time dependent representations of the electromagnetic field at close to the resolution of the computer display (Sundquist, 2003). The DLIC method, in particular, is far superior in delineating the spatial and temporal structure of fields as compared to e.g. field line displays or vector field grids. We also report on the use of these visualizations in instruction at the freshmen level. Our strong opinion is that for effective student learning, such visualizations must be embedded in a software framework for their interactive delivery. This "guided inquiry" framework is essential to influence and optimize what students take away from the visualizations. In our current research, we are delivering our visualizations using a commercial package, Addison Wesley's MasteringPhysics (MP), although any guided inquiry delivery system such as MP will be able to interact with our simulation software. We have released our Java 3D simulation software as open source with a liberal open source license (see http://jlearn.mit.edu/tealsim/), with support from the Davis Educational Foundation.

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Detecting the termination shock and beyond

AIP Conference Proceedings, 1999

Based on Voyager 2 observations, a numerical model of the heliosphere, which includes the mutual ... more Based on Voyager 2 observations, a numerical model of the heliosphere, which includes the mutual interaction of the interstellar medium, solar wind plasma, and interstellar hydrogen, is employed to speculate on the possible crossing of the termination shock b y the Voyager spacecraft. The multiple crossings caused by large-scale solar wind uctuations are studied quantitatively. In the event that Voyager 2 reaches the interstellar medium, the possibility of detecting interstellar ions with the MIT plasma experiment instrument (PLS) is discussed.

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Plasma Flow Turbulent Sheath

We find that the sheath regions between fast interplanetary mass ejections (ICMEs) and their prec... more We find that the sheath regions between fast interplanetary mass ejections (ICMEs) and their preceding shocks are often characterized by plasma depletion and mirror wave structures, analogous to planetary magnetosheaths. A case study of these signatures in the sheath of a magnetic cloud (MC) shows that a plasma depletion layer (PDL) coincides with magnetic field draping around the MC. In the same event, we observe an enhanced thermal anisotropy and plasma beta as well as anti-correlated density and magnetic fluctuations which are signatures of mirror mode waves. We perform a superposed epoch analysis of ACE and Wind plasma and magnetic field data from different classes of ICMEs to illuminate the general properties of these regions. For MCs preceded by shocks, the sheaths have a PDL with an average duration of 6 hours (corresponding to a spatial span of about 0.07 AU), a proton temperature anisotropy T ⊥p T p ≃ 1.2-1.3 and are marginally unstable to the mirror instability. Plasma depletion and mirror waves may also appear in the case of ICMEs with preceding shocks which are not MCs but at a reduced level. ICMEs without shocks are not associated with these features. These differences between the three ICME categories imply that these features depend on the ICME geometry and the extent of upstream solar wind compression by the ICMEs. We discuss the implications of these features for a variety of crucial physical processes including magnetic reconnection, formation of magnetic holes and energetic particle modulation in the solar wind. Sun ICME Plasma Flow Shock Field Lines Turbulent Sheath Figure 1. Schematic diagram of the turbulent sheath between an ICME and the preceding shock in the solar equatorial plane, illustrating the field line draping and consequent plasma flow.

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Design and Evaluation of a Learner-Centric Immersive Virtual Learning Environment for Physics Education

Lecture Notes in Computer Science, 2013

ABSTRACT There is a growing interest in virtual immersive environments such as virtual worlds for... more ABSTRACT There is a growing interest in virtual immersive environments such as virtual worlds for gaming, socialization, and also learning purpose. Frequently three major issues are mentioned, when using 3D worlds for educational scenarios: high technical requirements, low user acceptance and missing technical know-how. The last two issues can be decreased using an elaborate user-centric design with focus on the pedagogical objectives to improve the user experience and enhance the usability. This paper discusses design principles for immersive, three-dimensional environments and in-world tools with focus on pedagogical aspects and presents based on these principles an implementation of a virtual world environment for physics education which integrates the pedagogical model TEAL. A first showcase was built in Open Wonderland and evaluated and tested by student groups and domain experts with focus on usability and pedagogical ambitions. The evaluation shows how the implementation of a learning-centric model focusing on the pedagogical main objectives and designed in-line with the usability guidelines can minimize issues such as user acceptance and missing technical know-how.

Technology for active learning

Materials Today, 2003

Traditional science courses, even nowadays, present science as a collection of facts, while scien... more Traditional science courses, even nowadays, present science as a collection of facts, while scientific methodology is presented as homogeneous and based on empirical research. This leads to a static and context-independent view of discovery outcomes. Students are required to memorize facts without questioning either their development or relationship to other scientific or nonscientific knowledge 5. These problems, which result in high attrition and failure rates among students, have been found in both high school and undergraduate physics courses. Some researchers cite the lack of a common language between mathematicians and physicists as the root of learning difficulties experienced by physics students 6. Other studies place the blame on traditional teaching methods, which reward memorization over conceptual thinking 7 or just simply do not address adequately the needs of individual classes 8. Cognitive psychologists and educators have pointed to a strong relation between visual abilities and learning science 9. Problem solving in physics often requires visualizing abstract physical concepts or manipulating diagrams and graphs, demanding high visual and cognitive capabilities. Hestenes emphasized the necessity of developing teaching models that encourage conceptual understanding in physics classrooms 10. Teaching models are playing an increasing role in the science curriculum 11. Science educators and instructors agree that students need to understand the models of scientific phenomena with which they are presented 12 and to be able to construct their own 13. If students are to fully understand a model's nature and implications, it should cover a broad

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Temperature Anisotropy in a Shocked Plasma: Mirror-Mode Instabilities in the Heliosheath

The Astrophysical Journal, 2007

We show that temperature anisotropies induced at a shock can account for interplanetary and plane... more We show that temperature anisotropies induced at a shock can account for interplanetary and planetary bow shock observations. Shocked plasma with enhanced plasma beta is preferentially unstable to the mirror mode instability downstream of a quasi-perpendicular shock and to the firehose instability downstream of a quasi-parallel shock, consistent with magnetic fluctuations observed downstream of a large variety of shocks. Our theoretical analysis of the solar wind termination shock suggests that the magnetic holes observed by Voyager 1 in the heliosheath are produced by the mirror mode instability. The results are also of astrophysical interest, providing an energy source for plasma heating.

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Determining the Magnetic Field Orientation of Coronal Mass Ejections from Faraday Rotation

The Astrophysical Journal, 2007

We describe a method to measure the magnetic field orientation of coronal mass ejections (CMEs) u... more We describe a method to measure the magnetic field orientation of coronal mass ejections (CMEs) using Faraday rotation (FR). Two basic FR profiles, Gaussian-shaped with a single polarity or "N"-like with polarity reversals, are produced by a radio source occulted by a moving flux rope depending on its orientation. These curves are consistent with the Helios observations, providing evidence for the flux-rope geometry of CMEs. Many background radio sources can map CMEs in FR onto the sky. We demonstrate with a simple flux rope that the magnetic field orientation and helicity of the flux rope can be determined 2-3 days before it reaches Earth, which is of crucial importance for space weather forecasting. An FR calculation based on global magnetohydrodynamic (MHD) simulations of CMEs in a background heliosphere shows that FR mapping can also resolve a CME geometry curved back to the Sun. We discuss implementation of the method using data from the Mileura Widefield Array (MWA).

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Herbert S. Bridge

Physics Today, 1996

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How Does Technology-Enabled Active Learning Affect Undergraduate Students' Understanding of Electromagnetism Concepts?

Journal of the Learning Sciences, 2005

Educational technology supports meaningful learning and enables the presentation of spatial and d... more Educational technology supports meaningful learning and enables the presentation of spatial and dynamic images, which portray relationships among complex concepts. The Technology-Enabled Active Learning (TEAL) Project at the Massachusetts Institute of Technology (MIT) involves media-rich software for simulation and visualization in freshman physics carried out in a specially redesigned classroom to facilitate group interaction. These technology-based learning materials are especially useful in electromagnetism to help students conceptualize phenomena and processes. This study analyzes the effects of the unique learning environment of the TEAL project on students' cognitive and affective outcomes. The assessment of the project included examining students' conceptual understanding before and after studying electromagnetism in a media-rich environment. We also investigated the effect of this environment on students' preferences regarding the various teaching methods. As part of the project, we developed pre-and posttests consisting of conceptual questions from standardized tests, as well as questions designed to assess the effect of visualizations and experiments. The research population consisted of 811 undergraduate students. It consisted of a small-and a large-scale experimental groups and a control group. TEAL students improved their conceptual understanding

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How Much Have They Retained? Making Unseen Concepts Seen in a Freshman Electromagnetism Course at MIT

Journal of Science Education and Technology, 2007

The introductory freshmen electromagnetism course at MIT has been taught since 2000 using a studi... more The introductory freshmen electromagnetism course at MIT has been taught since 2000 using a studio physics format entitled TEAL-Technology Enabled Active Learning. TEAL has created a collaborative, hands-on environment where students carry out desktop experiments, submit web-based assignments, and have access to a host of visualizations and simulations. These learning tools help them visualize unseen electromagnetic concepts and develop stronger intuition about related phenomena. A previous study has shown that students who took the course in the TEAL format (the experimental group) gained significantly better conceptual understanding than those who took it in the traditional lecture-recitation format (the control group). The present longitudinal study focuses on the extent to which these two research groups (experimental and control) retain conceptual understanding about a year to 18 months after finishing the course. It also examines students attitudes about whether the teaching format (TEAL or traditional) contributes to their learning in advanced courses. Our research has indicated that the long-term effect of the TEAL course on studentsÕ retention of concepts was significantly stronger than that of the traditional course. This research is significant because it documents the long-term cognitive and affective impact of the TEAL studio physics format on learning outcomes of MIT students.

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Plasma depletion and mirror waves ahead of interplanetary coronal mass ejections

Journal of Geophysical Research: Space Physics, 2006

We find that the sheath regions between fast interplanetary coronal mass ejections (ICMEs) and th... more We find that the sheath regions between fast interplanetary coronal mass ejections (ICMEs) and their preceding shocks are often characterized by plasma depletion and mirror wave structures, analogous to planetary magnetosheaths. A case study of these signatures in the sheath of a magnetic cloud (MC) shows that a plasma depletion layer (PDL) coincides with magnetic field draping around the MC. In the same event, we observe an enhanced thermal anisotropy and plasma beta as well as anticorrelated density and magnetic fluctuations which are signatures of mirror mode waves. We perform a superposed epoch analysis of ACE and Wind plasma and magnetic field data from different classes of ICMEs to illuminate the general properties of these regions. For MCs preceded by shocks, the sheaths have a PDL with an average duration of 6 hours (corresponding to a spatial span of about 0.07 AU) and a proton temperature anisotropy T⊥p/T∥p ≃ 1.2–1.3, and are marginally unstable to the mirror instability. ...

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Constraints on the global structure of magnetic clouds: Transverse size and curvature

Journal of Geophysical Research, 2006

We present direct evidence that magnetic clouds (MCs) have highly flattened and curved cross sect... more We present direct evidence that magnetic clouds (MCs) have highly flattened and curved cross section resulting from their interaction with the ambient solar wind. Lower limits on the transverse size are obtained for three MCs observed by ACE and Ulysses from the latitudinal separation between the two spacecraft, ranging from 40°to 70°. The cross-section aspect ratio of the MCs is estimated to be no smaller than 6:1. We offer a simple model to extract the radius of curvature of the cross section, based on the elevation angle of the MC normal distributed over latitude. Application of the model to Wind observations from 1995 to 1997 (close to solar minimum) shows that the cross section is bent concavely outward by a structured solar wind with a radius of curvature of $0.3 AU. Near solar maximum, MCs tend to be convex outward in the solar wind with a uniform speed; the radius of curvature is proportional to the heliographic distance of MCs, as demonstrated by Ulysses observations between 1999 and 2003. These results improve our knowledge of the global morphology of MCs in the pre-Stereo era, which is crucial for space weather prediction and heliosphere studies.

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