Copyright (c) 2011 All rights reserved. http://works.bepress.com/tbensky Recent documents in Thomas Bensky en-us Fri, 25 Feb 2011 01:49:26 PST 3600 http://works.bepress.com/tbensky/17 http://works.bepress.com/tbensky/17 Wed, 23 Feb 2011 14:12:12 PST Gathering information from students for learning assessment is a critical need of any teacher. In this paper, the tech-savvy instructor is introduced to basic techniques of creating custom, web-based, student-data collection software. Despite widespread deployment of generalized course management systems, the author argues that small, ultra-customized data collection methodologies, can be of great help in collecting and assessing student input, reducing demands on paper, and easing the familiar grading bottleneck while satisfying an individual's pedagogical needs. Thomas J. Bensky Articles http://works.bepress.com/tbensky/16 http://works.bepress.com/tbensky/16 Wed, 20 Jan 2010 12:19:20 PST By posing a continual stream of pertinent questions, a nonmathematical computer program can prod freshman physics students toward an analytical solution to one-dimensional kinematics problems. Thomas J. Bensky Articles http://works.bepress.com/tbensky/15 http://works.bepress.com/tbensky/15 Mon, 04 Jan 2010 09:28:29 PST For instructors wishing to use physics as part of an international or general education course, the framework for a course based on the “longitude problem” from the 1700s is described. The longitude problem is teeming with basic principles of physics and astronomy, which makes it ideal for a non-science-major-based college-level course. This paper summarizes the longitude problem in the context of conceptual physics and astronomy and outlines an appropriate curriculum. Specifics on teaching such a course in London, as part of an international studies program, are discussed. Thomas J. Bensky Articles http://works.bepress.com/tbensky/14 http://works.bepress.com/tbensky/14 Wed, 07 Jan 2009 12:36:32 PST Unipolar “half-cycle” electric field pulses (HCPs) have been used to recombine free electrons and calcium ions. The field assisted process is very similar to controlled three-body recombination in plasmas. We report on experiments that utilize HCP assisted recombination to probe the probability distribution of continuum electron wave packets and produce bound wave packets that are highly localized in three spatial dimensions. Thomas J. Bensky Articles http://works.bepress.com/tbensky/13 http://works.bepress.com/tbensky/13 Wed, 07 Jan 2009 12:36:28 PST The oscillation between bound-state configurations in a rapidly autoionizing three-body Coulomb system has been directly observed. Using a 500-fsec laser pulse, calcium atoms are excited to the pure 4p3/215d two-electron configuration at an energy greater than 3 eV above the ionization limit. As a result of configuration interaction, the electrons scatter coherently into multiple bound and continuum configurations. The oscillation between the degenerate 4p1/2n′d and 4p3/2nd modes as well as autoionization into 4s1/2εl, 3d3/2εl, and 3d5/2εl continua are observed explicitly using bound-state interferometry. The measured time dependence of the 4p3/215d character is in excellent agreement with the Fourier transform of the frequency domain excitation cross section. To our knowledge, this is the first experimental demonstration of the equivalence of time and frequency domain spectra in a multiconfigurational system involving bound and continuum channels. M. B. Campbell Articles http://works.bepress.com/tbensky/12 http://works.bepress.com/tbensky/12 Wed, 07 Jan 2009 12:36:24 PST A method for experimentally measuring g, the Earth's gravitational acceleration, is presented. This method uses a computer joystick and computer as the primary measuring device. If a computer is available, it costs almost nothing to implement, and can be adapted for use as a high school or undergraduate lab exercise, or as a lecture demonstration. Thomas J. Bensky Articles http://works.bepress.com/tbensky/11 http://works.bepress.com/tbensky/11 Wed, 07 Jan 2009 12:36:20 PST An approach to experimentally measuring the speed of a moving object by direct application of the Doppler effect for sound is discussed. The method presented here uses a Windows computer and sound card to record Doppler shifted sound from a moving source. This sound card approach allows for direct acquisition of Doppler shifted sound intensity as a function of time, affording much analytical and pedagogical freedom in undergraduate lab instruction. In addition, the acquisition of such data allows for the experimental study of not only constant velocity sound sources, but of accelerated sound sources as well. Thomas J. Bensky Articles http://works.bepress.com/tbensky/10 http://works.bepress.com/tbensky/10 Wed, 07 Jan 2009 12:36:16 PST This paper provides a brief introduction to using ray-traced computer graphics for creating illustrations to be used in physics teaching. The article focuses on Povray, a freely available ray-tracing software program. We have found that a ray-traced illustration produced with this software provides a final-image quality that is far superior to hand-drawn illustrations and those produced using standard click-and-draw computer drawing software. Techniques for illustrating time-dependent scenarios are discussed as well. Thomas J. Bensky Articles http://works.bepress.com/tbensky/9 http://works.bepress.com/tbensky/9 Wed, 07 Jan 2009 12:36:12 PST Nighttime water-leaving radiance is a function of the depth-dependent distribution of both the in situ bioluminescence emissions and the absorption and scattering properties of the water. The vertical distributions of these parameters were used as inputs for a modified one-dimensional radiative transfer model to solve for spectral bioluminescence water-leaving radiance from prescribed depths of the water column. Variation in the water-leaving radiance was consistent with local episodic physical forcing events, with tidal forcing, terrestrial runoff, particulate accumulation, and biological responses influencing the shorter timescale dynamics. There was a >90 nm shift in the peak water-leaving radiance from blue (~474 nm) to green as light propagated to the surface. In addition to clues in ecosystem responses to physical forcing, the temporal dynamics in intensity and spectral quality of water-leaving radiance provide suitable ranges for assessing detection. This may provide the information needed to estimate the depth of internal light sources in the ocean, which is discussed in part 2 of this paper. Mark A. Moline Articles http://works.bepress.com/tbensky/8 http://works.bepress.com/tbensky/8 Wed, 07 Jan 2009 12:36:08 PST We report the first observation of ionization of Rydberg atoms by subpicosecond, circularly polarized THz radiation. The field amplitude in these pulses is non-negligible for only one-quarter of an optical cycle. The experiment is performed in the short-pulse regime, where the duration of the ionizing pulse is shorter than the classical Kepler period of the Rydberg electron. We find that the ionization probability for these atoms is remarkably insensitive to the time-varying polarization of the THz field. Thomas J. Bensky Articles http://works.bepress.com/tbensky/7 http://works.bepress.com/tbensky/7 Wed, 07 Jan 2009 12:36:04 PST Subpicosecond half-cycle pulses and a single-shot imaging detector have been used to monitor the evolution of electronic radial wave packets in calcium. The time-dependent momentum-space probability distribution is obtained using the impulsive momentum retrieval (IMR) method. The measured distributions are compared to the results of quantum and classical simulations allowing a comprehensive evaluation of the benefits and limitations of the IMR method. M. B. Campbell Articles http://works.bepress.com/tbensky/6 http://works.bepress.com/tbensky/6 Wed, 07 Jan 2009 12:36:00 PST Instructors who wish to implement an interactive lecture style, such as peer instruction, have the need to collect feedback from students in a lecture environment. We present a computer-controlled electronic circuit that allows for quick, rigorous, and accurate measurement and reporting of student feedback in the lecture environment. Thomas J. Bensky Articles http://works.bepress.com/tbensky/5 http://works.bepress.com/tbensky/5 Wed, 07 Jan 2009 12:35:56 PST Picosecond laser pulses have been used to produce Rydberg wave packets in calcium atoms in the presence of a strong static electric field. The dynamics of the Stark wave packets have been observed by measuring the momentum-space probability distribution as a function of time. The full precession of the electronic orbital angular momentum, the appearance of a large-amplitude, linear oscillation of the electronic dipole moment, and a pronounced, periodic up-down asymmetry in the momentum distribution are all observed directly. M. B. Campbell Articles http://works.bepress.com/tbensky/4 http://works.bepress.com/tbensky/4 Wed, 07 Jan 2009 12:35:52 PST Rydberg atoms are ionized by nearly unipolar, subpicosecond electromagnetic pulses. Deviations from a perfectly unidirectional pulse are found to alter substantially the ionization probability as a function of peak field. Quantitative agreement between classical theory and experiment is achieved if the pulse imperfections are significantly attenuated. N. E. Tielking Articles http://works.bepress.com/tbensky/3 http://works.bepress.com/tbensky/3 Wed, 07 Jan 2009 09:47:02 PST We have developed a new instrument for monitoring electronic wavepacket dynamics using a single electromagnetic pulse pair. The operation of the device is analogous to that of single-shot cross-correlators commonly used to monitor the temporal evolution of short laser pulses. We have used the instrument to probe wavepacket evolution over time scales ranging from 100 psec to less than 1 fsec. The device reduces the amount of time required to collect pump-probe time delay data by orders of magnitude, greatly reducing the deleterious effects of experimental drifts. In addition, the single-shot feature provides real-time feedback as to the affect of various experimental parameters on the electron dynamics, allowing us to literally tune-up our equipment to enhance desired behavior at specific times. M. B. Campbell Articles http://works.bepress.com/tbensky/2 http://works.bepress.com/tbensky/2 Tue, 06 Jan 2009 16:56:03 PST Seawater has been irradiated using a train of 70 ns flashes from a 440 nm laser source. This wavelength is on resonance with the blue absorption peak of Chlorophyll pigment associated with the photosystem of in vitro phytoplankton. The resulting fluorescence at 685 nm is instantaneously recorded during each laser pulse using a streak camera. Delayed fluorescence is observed, yielding clues about initiation of the photosynthetic process on a nanosecond time scale. Further data processing allows for determination of the functional absorption cross section, found to be 0:0095 Å2, which is the first reporting of this number for in vitro phytoplankton. Unlike other flash-pump studies of Chlorophyll, using a LED or flashlampbased sources, the short laser pulse used here does not reveal any pulse-to-pulse hysteresis (i.e., variable fluorescence), indicating that the laser pulses used here are not able to drive the photosynthetic process to completion. This is attributed to competition from a back reaction between the photoexcited photosystem II and the intermediate electron acceptor. The significance of this work as a new type of deployable ocean fluorimeter is discussed, and it is believed the apparatus will have applications in thin-layer phytoplankton research. Thomas J. Bensky Articles http://works.bepress.com/tbensky/1 http://works.bepress.com/tbensky/1 Tue, 06 Jan 2009 16:46:25 PST Thomas J. Bensky Course Readers