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Page 140 of 851

  • 21 - The Future of Planetary Rings Studies

  • from IV - Concluding Material
  • Edited by Matthew S. Tiscareno, Carl D. Murray, Queen Mary University of London
  • Book:
    Planetary Ring Systems
    Published online:
    26 February 2018
    Print publication:
    22 March 2018, pp 577-579

  • Summary

    INTRODUCTION

    The preceding chapters in this book have provided ample evidence for the growing maturity of planetary ring studies. The wealth of data, particularly from spacecraft observations, has resulted in the discovery of new phenomena and a total reevaluation of our knowledge of ring systems. Therefore, this seems like an appropriate point at which to assess progress and speculate on the future direction of research in this field.

    Planetary ring systems are among the most beautiful and iconic structures in the solar system, and continue to play a unique role as vehicles for discovery. This occurs in at least three ways: (i) as detectors of their environment, (ii) as records of the history and origin of their planetary system, and (iii) as natural laboratories for understanding astrophysical disks.

    The main rings of each of the giant planets are extensive but delicate systems, with surface areas that are far larger than those of neighboring moons. Therefore, while the surfaces of moons in outer planet systems provide a more permanent record of impacts and internal processes, rings can catch and amplify traces of planetary and interplanetary processes. Transient ejecta clouds provide direct evidence of the population of external impactors (Chapters 3 and 9), and corrugations in the rings of Jupiter and Saturn provide longer-lived records of larger impactors (Chapters 6 and 12). Patterns in dusty rings also give information regarding the nearby planetary magnetic fields (Chapters 12 and 14). Finally, spiral waves in dense rings impart detailed information about the moons that raise them (Chapter 3), and the precession of narrow rings yields some of the most accurate current knowledge of the internal structure of the giant planets (Chapter 11).

    Whether rings represent the material left over from the planetary formation process or the debris from a tidally disrupted object, they still provide invaluable evidence of the history and origin of their respective planetary systems. At Uranus, the apparently sourceless ν ring and the closely packed orbits of nearby small moons seem to tell of an eventful history for that planetary system (Chapter 4). Particle mass and size distributions and accompanying spectral data, including local variations across a ring system (see Chapter 3), constrain source materials and evolutionary histories while a proper understanding of all the dynamical processes at work is key to obtaining accurate estimates of the age of a ring system (Chapter 18).

  • Chapter 9 - Extraterrestrial INtelligence

  • Edited by David A. Rothery, The Open University, Milton Keynes, Iain Gilmour, The Open University, Milton Keynes, Mark A. Sephton, Imperial College London
  • Book:
    An Introduction to Astrobiology
    Published online:
    12 April 2019
    Print publication:
    01 March 2018, pp 301-326

  • Summary

    Introduction

    What do we mean by intelligence? This is not an easy question to answer in a philosophical sense. However, if we are willing to accept a subjective answer, then we can start by declaring that humans are intelligent. This still leaves a question mark over many other species on the Earth. If we are willing to be more specific still, then we can consider only intelligence that is capable of communicating signals across space. At present this is the only type of extraterrestrial intelligence we can hope to discover. So, for the purposes of this chapter, when we refer to intelligent life it should be understood that we mean life that can engage in interstellar communication. (In this pragmatic usage, humans have been ‘intelligent’ for only a few decades and Newton, Darwin and many other great scientists of the past don't actually qualify as having been intelligent life.)

    With our pragmatic interpretation of intelligence, SETI, the Search for Extraterrestrial Intelligence, is a well-defined problem: we must search for signals from life elsewhere in the Universe. Given our current technology, only signals transmitted as electromagnetic radiation are detectable, though there is also the possibility that we may be visited by an alien spacecraft or encounter a robotic messenger device. A plausible example of the latter would be an autonomous interstellar probe, probably with a high level of artificial intelligence, loaded with information that its home civilization wished to share. Such a device is known as a Bracewell probe, after the Australian scientist Ronald Bracewell (1921–2007) who proposed the concept in 1960. A Bracewell probe could be intended to be encountered physically, or a short-range (less than interstellar) communications strategy could be used, but in either case it would need to travel at least decades and maybe far longer to reach us. Seeking signs of alien artifacts, ranging from small probes to colossal works of astroengineering, is referred to as SETA (Search for Extraterrestrial Artifacts). We will focus here on searching for signals originating from the alien's home planet, and thus on SETI rather than SETA.

  • Resources

  • Yoni Kahn, Princeton University, New Jersey, Adam Anderson
  • Book:
    Conquering the Physics GRE
    Published online:
    16 February 2018
    Print publication:
    01 March 2018, pp xii-xiv

  • Summary

    Here we collect all the texts we recommend and will refer to in the review chapters. If you're wondering why books by Griffiths show up so often, it's likely because he was on the question-writing committee for the Physics GRE several years ago. Anecdotally, we know that questions are recycled very often (which is why so few exams have been released), so it's likely that many of the questions you'll see on your exam were written by Griffiths or consciously modeled after his books.

  • • Classical Mechanics: Whatever book you used for freshman physics should suffice here. For a more in-depth review of advanced topics, try Classical Dynamics of Particles and Systems by S.T. Thornton and J.B. Marion.

  • • Electricity and Magnetism: D.J. Griffiths, Introduction to Electrodynamics. This book covers everything you'll need to know about electricity and magnetism on the GRE, except for circuits. For circuits and a review of the most basic electricity andmagnetism problems, which Griffiths glosses over, consult any standard freshman physics textbook. A good treatment of electromagnetic waves can also be found in R.K. Wangsness, Electromagnetic Fields. E. Purcell, Electricity and Magnetism is an extremely elegant introduction emphasizing physical concepts rather than mathematical formalism, should you need to relearn the basics of any topic. Under no circumstances should you consult Jackson! It's far too advanced for anything you'll need for the GRE.

  • • Optics and Waves: Like classical mechanics, nearly all the relevant information is covered in your freshman physics textbook. Anything you're missing can be found in the relevant chapters of Introduction to Electrodynamics by Griffiths.

  • • Thermodynamics and Statistical Mechanics: No overwhelming recommendation here. Thermal Physics and Elementary Statistical Physics by C. Kittel, or Fundamentals of Statistical and Thermal Physics by F. Reif, are decent. Statistical Physics, by F. Mandl has some decent pedagogy and the nice feature of many problems with worked solutions. Fermi's Thermodynamics is a classic for the most basic aspects of the subject.

  • Preface

  • Yoni Kahn, Princeton University, New Jersey, Adam Anderson
  • Book:
    Conquering the Physics GRE
    Published online:
    16 February 2018
    Print publication:
    01 March 2018, pp ix-x

  • Summary

    Conquering the Physics GRE represents the combined efforts of two MIT graduate students frustrated with the lack of decent preparation materials for the Physics GRE subject test. When we took the exams, in 2007 and 2009, we did what any student in the internet age would do – searched the various online bookstores for “physics GRE prep,” “physics GRE practice tests,” and so on. We were puzzled when the only results were physics practice problems that had nothing to do with the GRE specifically or, worse, GRE practice books having nothing to do with physics. Undeterred, we headed to our local brick-and-mortar bookstores, where we found a similar situation. There were practice books for every single GRE subject exam, except physics. Further web searches unearthed www.grephysics.net, containing every problem and solution from every practice test released up to that point, and www.physicsgre.com, a web forum devoted to discussing problems and strategies for the test. We discovered these sites had sprung up thanks to other frustrated physicists just like us: there was no review material available, so students did the best they could with the meager material that did exist. This situation is particularly acute for students in smaller departments, who have fewer classmates with whom to study and share the “war stories” of the GRE.

    This book endeavors to fix that situation. Its main contribution is a set of three full-length practice tests and fully worked solutions, designed to be as close as possible in style, difficulty, content distribution, and format to the actual GRE exam. We have also included review material for all of the nine content areas on the Physics GRE exam: classical mechanics, electricity and magnetism, optics and waves, thermodynamics and statistical mechanics, quantum mechanics, atomic physics, special relativity, laboratory methods, and specialized topics. To our knowledge, this is the first time that reviews of standard undergraduate subjects such as classical mechanics and thermodynamics have been paired with less standard it material such as laboratory methods in the same text, specifically focused on aspects of these subjects relevant for the GRE. Exam-style practice problems and worked solutions are included for each review chapter, giving over 150 additional GRE-style practice problems in addition to the 300 from the exams. The shorter chapters have review problems at the very end, while the longer ones have review problems distributed throughout the chapter.

  • 8 - Specialized Topics

  • Yoni Kahn, Princeton University, New Jersey, Adam Anderson
  • Book:
    Conquering the Physics GRE
    Published online:
    16 February 2018
    Print publication:
    01 March 2018, pp 146-158

  • Summary

    The Specialized Topics questions on the Physics GRE are probably the most unique aspect of the test. It's hard to think of any other test (other than TV game shows) in which a full 10% is random assorted knowledge. This may seem daunting, but with smart preparation, these questions actually offer a huge advantage.

    The special topics questions are almost entirely pure knowledge recall, otherwise known as fact regurgitation. This is the kind of knee-jerk memorization you probably hated in high-school chemistry or biology. When confronted by a special topics question, you'll either know it or you won't. If you know it, that's one question down in under 10 seconds, which gives you a huge bonus on time for the more difficult calculational questions. If you don't know it, you probably won't be able to figure out the answer just by reasoning through it, and you may waste 5 or more minutes second-guessing yourself when stuck between two equally appealing answer choices. The optimum strategy, then, is to amass a basic knowledge of as many areas of cutting-edge physics as possible, just enough to make the associations between “buzzwords” and concepts that will allow you to recall the required knowledge.

    Luckily, this kind of studying is dead easy. Every couple days, take a break from your normal Physics GRE practice and just read. Pick up a basic textbook in an advanced subject you're unfamiliar with (for example, if you're aiming towards high-energy, choose an introductory solid-state physics or electrical engineering textbook), and don't bother working any problems; just read the book as if it were a novel. You might learn something new and interesting, but that's not really the point: by reading this way, you'll be forming connections and associations in your memory that you might not even be aware of. It's likely you won't be able to remember exactly what you read, but if prompted by a keyword that shows up on the GRE, your memory will spring into action with that feeling of “I've seen this somewhere before.” That's really all you need for these kinds of questions.

Page 140 of 851