Search Results

Inertial confinement by spherical implosion

Stefano Atzeni and JÜrgen Meyer-Ter-Vehn

in The Physics of Inertial Fusion: BeamPlasma Interaction, Hydrodynamics, Hot Dense Matter

The concept of inertial confinement fusion (ICF) is to burn a few milligrams of fuel compressed to more than 1000 times liquid density within the time interval in which mass inertia keeps the burning ... More

The concept of inertial confinement fusion (ICF) is to burn a few milligrams of fuel compressed to more than 1000 times liquid density within the time interval in which mass inertia keeps the burning fuel together. The required densities can be obtained by imploding a spherical shell ‘target’ (or ‘capsule’) by high-power radiation (laser beams, ion beams, X-rays). Deposition of the beam energy leads to heating and ablation of the surface of the shell and generates the pressure that drives the implosion. The stages of shell implosion, ignition, and propagating burn are then essentially independent of the driver and the irradiation scheme. This chapter discusses the principles of inertial confinement fusion in a simple, almost self-contained manner, and illustrates them by 1-D simulation results of the implosion of a typical direct-drive laser-driven ICF target. Aspects of implosion symmetry are discussed and illustrated by 2-D simulations. The energy output of ICF reactor-size targets is also briefly described.Less

Hohlraum targets

Stefano Atzeni and JÜrgen Meyer-Ter-Vehn

in The Physics of Inertial Fusion: BeamPlasma Interaction, Hydrodynamics, Hot Dense Matter

Hohlraum targets are a special class of ICF targets, in which capsule ablation is driven by the thermal radiation inside a cavity, the so-called hohlraum. In this scheme, the laser or ion beams do ... More

Hohlraum targets are a special class of ICF targets, in which capsule ablation is driven by the thermal radiation inside a cavity, the so-called hohlraum. In this scheme, the laser or ion beams do not drive the capsule directly, and one therefore calls it indirect drive. Expressions for X-ray conversion efficiency are derived for incident laser and ion beams. Radiation confinement inside the cavity is discussed in terms of the wall albedo, which measures the re-emission of absorbed radiation by the heated wall. The radiative transfer between the walls is treated approximately by means of the viewfactor method. Simple estimates are derived for the hohlraum temperature of the black-body radiation. Simulations of radiatively driven implosions are presented in the context of targets for ion beam fusion.Less

1945 and the Atomic Bomb

Colin F. Baxter

in The Secret History of RDX: The Super-Explosive that Helped Win World War II

World War II ended with unexpected suddenness. The dropping of two atomic bombs appeared to make conventional explosives obsolete; however, RDX and Composition B played a critical role in creating ... More

World War II ended with unexpected suddenness. The dropping of two atomic bombs appeared to make conventional explosives obsolete; however, RDX and Composition B played a critical role in creating the detonation shockwave that “squeezed” the plutonium core of the “Fat Man” bomb that was dropped on Nagasaki, Japan.Less

The Beaubourg Effect: Implosion and Deterrence

Steve Redhead

in The Jean Baudrillard Reader

This chapter is an extract from Baudrillard’s Simulacra and Simulation, with an editorial overview

Moral Sphere Collapses

Philippe Rochat

in Moral Acrobatics: How We Avoid Ethical Ambiguity by Thinking in Black and White

We live in well-separated moral spheres, typically well compartmentalized, but they can collapse. These spheres are delimited by context and people, each calling for different moral biases and codes. ... More

We live in well-separated moral spheres, typically well compartmentalized, but they can collapse. These spheres are delimited by context and people, each calling for different moral biases and codes. We develop a remarkable ability to switch moral codes depending on people and circumstances, as exemplified by Hitler and his pet dog or Ariel Castro with his child and neighbors. However, collapse between these spheres may happen causing great anxieties and, in some instances, can be lethal. Moral code implosions due to such collapse are the main cause of guilt, a major conundrum of human psychology.Less

A Heart Made of Abundance

Philippe Rochat

in Moral Acrobatics: How We Avoid Ethical Ambiguity by Thinking in Black and White

The fictive story of John wearing multiple hats for one head and his sudden mental collapse is an illustration of what personhood might be, in particular the true nature of who we are as moral ... More

The fictive story of John wearing multiple hats for one head and his sudden mental collapse is an illustration of what personhood might be, in particular the true nature of who we are as moral agents. The self as moral agent is a process, not a static thing. There is no objective moral agent in itself, just as there is no objective cloud in itself: there is just something revealed in transition. The self as moral agent is revealed in transition from code to code, sphere to sphere, like the cloud is revealed by the constant transition of air masses from gas to solid state.Less

Specific Phobias

Vladan Starcevic, MD, PhD

in Anxiety Disorders in Adults: A Clinical Guide

Specific phobias (also referred to as simple phobias and isolated phobias) represent a heterogeneous group of disorders characterized by excessive and/or irrational ... More

Specific phobias (also referred to as simple phobias and isolated phobias) represent a heterogeneous group of disorders characterized by excessive and/or irrational fear of one of relatively few and usually related objects, situations, places, phenomena, or activities (phobic stimuli). The phobic stimuli are either avoided or endured with intense anxiety or discomfort. People with specific phobias are aware that their fear is unreasonable, but this does not diminish the intensity of the fear. Rather, they are quite distressed about being afraid or feel handicapped by their phobia. Specific phobias are frequently encountered in the general population, but they are relatively uncommon in the clinical setting. Most phobias have a remarkable tendency to persist, prompting an assumption that they cannot be easily extinguished because of their ‘‘purpose’’ to protect against danger. Specific phobias are deceptively simple, as they are easy to describe and recognize but often difficult to understand. There are several conceptual problems and a number of issues associated with specific phobias:… 1. Where are the boundaries of specific phobias? How can we develop better criteria on the basis of which specific phobia could be distinguished as a psychiatric disorder from fears and avoidance considered to be within the realm of ‘‘normality?’’ 2. How can specific phobias be taken seriously by both the sufferers and clinicians? 3. In view of the considerable differences between various types of specific phobias, should they continue to be grouped together? 4. Should specific phobias be grouped on the basis of whether they are driven by fear or disgust? 5. In view of its unique features, should the blood-injection-injury type of specific phobia be given a separate psychopathological, diagnostic, and nosological status? 6. Considering a significant overlap between situational phobias and agoraphobia, should they be grouped together, along a hypothetical situational phobia/agoraphobia spectrum? 7. What is the relationship between specific phobias and other psychopathology? Are they relatively isolated from other disorders, both cross-sectionally and longitudinally, or should they more appropriately be conceptualized as a predisposition to or a risk factor for some psychiatric conditions? 8. How specific are pathways that lead to specific phobias? 9. Has the dominant treatment model for specific phobias, based on exposure therapy, exhausted its potential? Is the tendency for specific phobias to persist adequately addressed by treatments derived from learning theory? Less

Production, Uses, and Stocks of Fissile Materials

Harold A. Feiveson

in Unmaking the Bomb: A Fissile Material Approach to Nuclear Disarmament and Nonproliferation

Fissile materials can sustain a nuclear chain reaction and are used in weapons and as reactor fuels. This chapter explains the production and use of the most common fissile materials, highly enriched ... More

Fissile materials can sustain a nuclear chain reaction and are used in weapons and as reactor fuels. This chapter explains the production and use of the most common fissile materials, highly enriched uranium and plutonium. The highly enriched uranium typically used in weapons is enriched to 90 percent or higher in the isotope uranium-235. Gaseous diffusion was used to produce most of the highly enriched uranium in the world, but has been replaced by gas centrifuge technology. Plutonium is produced from uranium in reactors and separated from spent nuclear fuel in a reprocessing plant. Plutonium of almost any isotopic composition, including that produced in civilian power reactors, is weapons usable. In the bomb that destroyed Hiroshima, a gun-type assembly was used to create a supercritical mass of highly enriched uranium able to sustain an explosive chain reaction, while the Nagasaki weapon used a plutonium implosion compression assembly. In modern thermonuclear weapons, an implosion fission “primary” ignites a fusion-fission “secondary.” Such weapons generally typically contain about 3?4 kilograms of plutonium and 15?25 kilograms of highly enriched uranium.Less

Beowulf: Dragon Slayer (1975)

Chris Bishop

in Medievalist Comics and the American Century

Failure can be just as illuminating as success, and so this looks at the alarmingly short-lived Beowulf: Dragon Slayer. By the mid-1970s, when the Anglo-Saxon hero appeared in his own title series, ... More

Failure can be just as illuminating as success, and so this looks at the alarmingly short-lived Beowulf: Dragon Slayer. By the mid-1970s, when the Anglo-Saxon hero appeared in his own title series, Beowulf, the Anglo-Saxon poem, was yet to transition from an academic to a popular milieu, and a continuous and steadfastly nationalist interpretation made it very difficult for the poem’s eponymous hero to get the sort of traction enjoyed by folk heroes such as Robin Hood or Thor. Subsequently, Beowulf: Dragon Slayer, despite the innate worthiness of its subject and despite the efforts of DC heavyweights like Michael Uslan, was doomed before issue one hit the newsstands.Less

Limiting behavior of Julia sets of singularly perturbed rational maps

Robert L. Devaney

Araceli Bonifant, Mikhail Lyubich, and Scott Sutherland (eds)

in Frontiers in Complex Dynamics: In Celebration of John Milnor's 80th Birthday

This chapter surveys dynamical properties of the families fsubscript c,𝜆(z) = zⁿ + c + λ‎/zᵈ for n ≥ 2, d ≥ 1, with c corresponding to the center of a hyperbolic component of the Multibrot set. These ... More

This chapter surveys dynamical properties of the families fsubscript c,𝜆(z) = zⁿ + c + λ‎/zᵈ for n ≥ 2, d ≥ 1, with c corresponding to the center of a hyperbolic component of the Multibrot set. These rational maps produce a variety of interesting Julia sets, including Sierpinski carpets and Sierpinski gaskets, as well as laminations by Jordan curves. The chapter describes a curious “implosion” of the Julia sets as a polynomial psubscript c = zⁿ + c is perturbed to a rational map fsubscript c,𝜆. In this way the chapter shows yet another way of producing rational maps through “singular” perturbations of complex polynomials.Less