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The geometry of small causal diamonds is systematically studied, based on three distinct constructions that are common in the literature, namely the geodesic ball, the Alexandrov interval and the light cone cut. The causal diamond geometry is calculated perturbatively using Riemann normal coordinate expansion up to the leading order in both vacuum and nonvacuum. We provide a collection of results including the area of the codimension-two edge, the maximal hypersurface volume and their isoperimetric ratio for each construction, which will be useful for any applications involving the quantitative properties of causal diamonds. In particular, by solving the dynamical equations of the expansion and the shear on the light cone, we find that intriguingly only the light cone cut construction yields an area deficit proportional to the Bel-Robinson superenergy density W in four-dimensional spacetime, but such a direct connection fails to hold in any other dimension. We also compute the volume of the Alexandrov interval causal diamond in vacuum, which we believe is important but missing from the literature. Our work complements and extends the earlier works on the causal diamond geometry by Gibbons and Solodukhin [Phys. Lett. B 649, 317 (2007)], Jacobson, Senovilla and Speranza [Classical Quantum Gravity 35, 085005 (2018)] and others [J. Myrheim, CERN Report No. CERN-TH-2538, 1978; M. Roy, D. Sinha, and S. Surya, Phys. Rev. D 87, 044046 (2013); I. Jubb, Classical Quantum Gravity 34, 094005 (2017)]. Some potential applications of our results in mathematical general relativity and quantum gravity are discussed.
Three causal diamond constructions are illustrated here. The size parameter l (green), orientation Ua (yellow), diamond edge Sl (blue) and diamond origin O are indicated for each causal diamond. Σ specifies the spacelike hypersurface with maximal volume and its domain of dependence D(Σ) defines the causal diamond DSl.
Infrared spectra indicate the coordination of the ligand to the metal ions through the oxygen of the P=O group. IR and conductance show that the nitrate groups are all coordinated. Electronic spectral shapes have been interpreted in terms of an eight coordinate geometry around the metal ions.
In this video David rapidly explains all the concepts in 1D motion and also quickly solves a sample problem for each concept. Keep an eye on the side scroll see how far along you've made it in the review video. Created by David SantoPietro.
In this video David quickly explains each 2D motion concept and does a quick example problem for each concept. Keep an eye on the scroll to the right to see where you are in the review. Created by David SantoPietro.
This 12 session course is designed for the beginning or novice archer and uses recurve indoor target bows and equipment. The purpose of the course is to introduce students to the basic techniques of indoor target archery emphasizing the care and use of equipment, range safety, stance and shooting techniques, scoring and competition.
Students use ultrasonic sensors and LEGO MINDSTORMS NXT robots to emulate how bats use echolocation to detect obstacles. They measure the robot's reaction times as it senses objects at two distances and with different sensor threshold values, and again after making adjustments to optimize its effectiveness. Like engineers, they gather and graph data to analyze a given design (from the tutorial) and make modifications to the sensor placement and/or threshold values in order to improve the robot's performance (iterative design). Students see how problem solving with biomimicry design is directly related to understanding and making observations of nature.
Students learn how engineers gather data and model motion using vectors. They learn about using motion-tracking tools to observe, record, and analyze vectors associated with the motion of their own bodies. They do this qualitatively and quantitatively by analyzing several examples of their own body motion. As a final presentation, student teams act as engineering consultants and propose the use of (free) ARK Mirror technology to help sports teams evaluate body mechanics. A pre/post quiz is provided.
This is a really fun and informative lesson that I do with my high school Programming/technology class to break up the monotony of beginner programming. However; this lesson can be used and applied in essentially any class and for many purposes, and to address many areas. One of the other really nice things about this lesson is that it can be extended to hit many points including physics, math, and advanced engineering.
In this task students interpret two graphs that look the same but show very different quantities. The first graph gives information about how fast a car is moving while the second graph gives information about the position of the car. This problem works well to generate a class or small group discussion. Students learn that graphs tell stories and have to be interpreted by carefully thinking about the quantities shown.
An interactive applet and associated web page that demonstrate how to find the perpendicular distance between a point and a line using trigonometry, given the coordinates of the point and the slope/intercept of the line. The applet has a line with sliders that adjust its slope and intercept, and a draggable point. As the line is altered or the point dragged, the distance is recalculated. The grid and coordinates can be turned on and off. The distance calculation can be turned off to permit class exercises and then turned back on the verify the answers. The applet can be printed as it appears on the screen to make handouts. The web page has a full description of the concept of the concepts, a worked example and has links to other pages relating to coordinate geometry. Applet can be enlarged to full screen size for use with a classroom projector. This resource is a component of the Math Open Reference Interactive Geometry textbook project at
Students' understanding of how robotic ultrasonic sensors work is reinforced in a design challenge involving LEGO MINDSTORMS(TM) NXT robots and ultrasonic sensors. Student groups program their robots to move freely without bumping into obstacles (toy LEGO people). They practice and learn programming skills and logic design in parallel. They see how robots take input from ultrasonic sensors and use it to make decisions to move, resulting in behavior similar to the human sense of sight but through the use of sound sensors, more like echolocation. Students design-test-redesign-retest to achieve successful programs. A PowerPoint presentation and pre/post quizzes are provided.
Students develop and solidify their understanding of the concept of "perimeter" as they engage in a portion of the civil engineering task of land surveying. Specifically, they measure and calculate the perimeter of a fenced in area of "farmland," and see that this length is equivalent to the minimum required length of a fence to enclose it. Doing this for variously shaped areas confirms that the perimeter is the minimal length of fence required to enclose those shapes. Then students use the technology of a LEGO MINDSTORMS(TM) NXT robot to automate this task. After measuring the perimeter (and thus required fence length) of the "farmland," students see the NXT robot travel around this length, just as a surveyor might travel around an area during the course of surveying land or measuring for fence materials. While practicing their problem solving and measurement skills, students learn and reinforce their scientific and geometric vocabulary.
Following is a complete list of doctoral graduates of the Department of Computer Science, with their dissertation titles. Graduates of other departments or schools, whose primary adviser was a member of the Department of Computer Science, are also listed.
UNC Libraries: Except where noted, all of the dissertations listed here are available from the libraries at UNC-Chapel Hill. Those from the most recent year will not immediately be available, however.
See-through near-eye displays with the form factor and field of view of eyeglasses are a natural choice for augmented reality systems: the non-encumbering size enables casual and extended use and large field of view enables general-purpose spatially registered applications. However, designing displays with these attributes is currently an open problem. Support for enhanced realism through mutual occlusion and the focal depth cues is also not found in eyeglasses-like displays.
This dissertation provides a new strategy for eyeglasses-like displays that follows the principles of computational displays, devices that rely on software as a fundamental part of image formation. Such devices allow more hardware simplicity and flexibility, showing greater promise of meeting form factor and field-of-view goals while enhancing realism. This computational approach is realized in two novel and complementary see-through near-eye display designs. The first subtractive approach filters omnidirectional light through a set of optimized patterns displayed on a stack of spatial light modulators, reproducing a light field corresponding to in-focus imagery. The design is thin and scales to wide fields of view; see-through operation is achieved with transparent components placed directly in front of the eye. Preliminary support for focal cues and environment occlusion is also demonstrated. The second additive approach uses structured point light illumination to form an image with a near minimal set of rays. Each of an array of defocused point light sources is modulated by a region of a spatial light modulator, essentially encoding an image in the focal blur. See-through operation is also achieved with transparent components, and thin form factors and wide fields of view >100 degrees are demonstrated.
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