A simple 5-DOF walking robot for space station application

Robots on the NASA space station have a potential range of applications from assisting astronauts during EVA (extravehicular activity), to replacing astronauts in the performance of simple, dangerous, and tedious tasks; and to performing routine tasks such as inspections of structures and utilities. To provide a vehicle for demonstrating the pertinent technologies, a simple robot is being developed for locomotion and basic manipulation on the proposed space station. In addition to the robot, an experimental testbed was developed, including a 1/3 scale (1.67 meter modules) truss and a gravity compensation system to simulate a zero-gravity environment. The robot comprises two flexible links connected by a rotary joint, with a 2 degree of freedom wrist joints and grippers at each end. The grippers screw into threaded holes in the nodes of the space station truss, and enable it to walk by alternately shifting the base of support from one foot (gripper) to the other. Present efforts are focused on mechanical design, application of sensors, and development of control algorithms for lightweight, flexible structures. Long-range research will emphasize development of human interfaces to permit a range of control modes from teleoperated to semiautonomous, and coordination of robot/astronaut and multiple-robot teams

Decay rate and other properties of the positronium negative ion

A new method for detecting the positronium minus ion is described, and the possibility of a long positronium mean free path in a solid is discussed

Not Everyone Works for BigLaw: A Response to Neil J. Dilloff

In a law review article entitled The Changing Cultures and Economics of Large Law Firm Practice and Their Impact on Legal Education, DLA Piper partner Neil J. Dilloff details recent changes in the way that BigLaw does business. He then suggests a number of improvements in legal education ostensibly compelled by the new economic realities of large firm practice. While many of Attorney Dilloff\u27s suggestions make very good sense, several problems exist. In this short essay, we take the position that law schools should not pattern current reforms solely on the needs of BigLaw. Instead, we suggest that reforming legal education requires law schools to rethink the tradition of merely teaching students to think like lawyers. Rather than upholding the status quo of a generally liberal arts pursuit to the study of law, law school curricula, particularly in upper-division classes, should focus on producing lawyers ready and able to practice in a variety of contexts

Pair Events in Superluminal Optics

When an object moves faster than emissions it creates, it may appear at two positions simultaneously. The appearance or disappearance of this bifurcation is referred to as a pair event. Inherently convolved with superluminal motion, pair events have no subluminal counterparts. Common examples of superluminal motions that exhibit pair events include Cherenkov radiation, sonic booms, illumination fronts from variable light sources, and rotating beams. The minimally simple case of pair events from a single massive object is explored here: uniform linear motion. A pair event is perceived when the radial component of the object's speed toward the observer drops from superluminal to subluminal. Emission from the pair creation event will reach the observer before emission from either of the two images created. Potentially observable image pair events are described for sonic booms and Cherenkov light. To date, no detection of discrete images following a projectile pair event have ever been reported, and so the pair event nature of sonic booms and Cherenkov radiation, for example, remains unconfirmed. Recent advances in modern technology have made such pair event tracking feasible. If measured, pair events could provide important information about object distance and history.Comment: 13 pages, 3 figures. in press: Annalen der Physi

Explanation, prediction, causation – an unholy trinity? Appreciative comments on Philosophy and Methods in Political Science

In this short but critical appreciation of Keith Dowding’s seminal Philosophy and Methods of Political Science I reflect on the distinctive treatment of both realism and explanation in contemporary political science that its author offers, expressing rather more sympath y for the former than the latter. I welcome his critique of the use and misuse of ‘isms’ in much of the existing literature, whilst pointing to some potential inconsistencies; I accept his broad and inclusive understanding of philosophic realism; and I pr aise Dowding for putting the question of explanation – and its adequacy – at the heart of the philosophy of political science (where I think it belongs). Yet I reject the idea that prediction is or, indeed, should be central to all social scientific expla nation. Similarly I take issue with the contention that we are typically distracted by questions of causation, suggesting that the presentation of a ‘credibly causal’ narrative is the crux of adjudicating good from bad explanation. I explore the implicat ions of such a position and conclude with comments on Dowding’s call for the reproducibility and transparency of data

Cross Border State Sales and Use Taxation After \u3ci\u3eSouth Dakota v. Wayfair\u3c/i\u3e: A New Paradigm for E-Commerce

For over 50 years, U.S. Supreme Court precedents held that state sales taxes could not be constitutionally applied against retailers with no physical presence in the taxing states. As a result, many states implemented use tax laws to supplement sales tax laws, essentially requiring each resident consumer to self-report and pay taxes on purchases made from out of state retailers. However, these use tax laws were largely ignored. Moreover, with the advent of online retail (“e-tail”), many sales on which states previously collected sales tax from local stores essentially converted to “tax-free” sales because many online sellers (“e-tailers”) had no physical nexus to the states in which the products were delivered. As online sales continued to take up a larger percentage of all purchases, states struggled to secure sales and use tax revenue consistent with the physical nexus standard. In recent years, many states implemented laws that required e-tailers to collect sales taxes not based upon physical presence, but upon annual dollar value or number of sales into the states (called, “economic nexus”). However, enforceability of the economic nexus laws was questionable in light of past U.S. Supreme Court decisions. Additionally, with more than 9,600 sales taxing jurisdictions with varying rules and rates, many argued that compliance would create an undue burden on interstate commerce in violation of the Commerce Clause of the U.S. Constitution. South Dakota was one of the states to implement an economic nexus law, and it was challenged on constitutional grounds. In June 2018, in the matter of South Dakota v. Wayfair, et al., the U.S. Supreme Court held in favor of South Dakota, overturning the physical nexus standard and allowing economic nexus sales taxation of online sales based upon dollar value or number of sales alone. This article summarizes state sales and use tax laws, prior Supreme Court precedent, and the South Dakota v. Wayfair decision. It then examines current economic nexus and similar laws, compliance issues, and possible solutions for the e-tailer client

Algorithms for Highly Symmetric Linear and Integer Programs

This paper deals with exploiting symmetry for solving linear and integer programming problems. Basic properties of linear representations of finite groups can be used to reduce symmetric linear programming to solving linear programs of lower dimension. Combining this approach with knowledge of the geometry of feasible integer solutions yields an algorithm for solving highly symmetric integer linear programs which only takes time which is linear in the number of constraints and quadratic in the dimension.Comment: 21 pages, 1 figure; some references and further comments added, title slightly change

Transistor Circuits

Contains reports on three research projects