Physics of Particle Detection

In this review the basic interaction mechanisms of charged and neutral particles are presented. The ionization energy loss of charged particles is fundamental to most particle detectors and is therefore described in more detail. The production of electromagnetic radiation in various spectral ranges leads to the detection of charged particles in scintillation, Cherenkov and transition radiation counters. Photons are measured via the photoelectric effect, Compton scattering or pair production, and neutrons through their nuclear interactions. A combination of the various detector methods helps to identify elementary particles and nuclei. At high energies absorption techniques in calorimeters provide additional particle identification and an accurate energy measurement.Comment: 32 pages, LaTeX, 21 figure

Tumour Therapy with Particle Beams

Photons are exponentially attenuated in matter producing high doses close to the surface. Therefore they are not well suited for the treatment of deep seated tumours. Charged particles, in contrast, exhibit a sharp increase of ionisation density close to the end of their range, the so-called Bragg-peak. The depth of the Bragg-peak can be adjusted by varying the particle's energy. In parallel with the large energy deposit the increase in biological effectiveness for cell killing at the end of the range provides an ideal scalpel for the surgeon effectively without touching the surface tissue. Consequently proton therapy has gained a lot of ground for treating well localized tumours. Even superior still are heavy ions, where the ionisation pattern is increased by the square of their charge.Comment: 12 pages, Latex, 11 figure

High-level planning for dextrous manipulation

Journal ArticleThe development of mechanical end effectors capable of dextrous manipulation is a rapidly growing and quite successful field of research. It has in some sense put the focus on control issues, in particular, how to control these remarkably anthropomorphic manipulators to perform the deft movement that we take for granted in the human hand. The objective of this paper is the creation of a framework within which constraints involving the manipulator, the object, and the hand/object interaction can be exploited to direct a goal oriented manipulation. The analysis here is targeted for the Utah/MIT dextrous manipulator, but will support any general purpose dextrous manipulation system?

Task defined grasp force solutions

Journal ArticleForce Control for dextrous manipulation has been approached algebraically with a great deal of success, however, the computational burden created when such approaches are applied to grasps consisting of many contacts is prohibitive. This paper describes a procedure which restricts the complexity of the algebraic system of equations, and makes use of mathematical programming techniques to select a solution which is optimal with respect to an objective function. The solution is constrained by contact surface friction properties and the kinematic limitations of the hand. The application of the procedure to the selection of minimal internal grasp forces which allow the application of task defined external forces is described. Examples of the procedure are presented

Apparent symmetries in range data

technical reportA procedure for extracting symmetrical features from the output of a range scanner is described which is insensitive to sensor noise and robust with respect to object surface complexity. The acquisition of symmetry descriptors for rigid bodies from a range image was in this case motivated by the need to direct pre-grasp configurations in dextrous manipulation systems. However, object symmetries are powerful features for object identification/matching and correspond explicitly to useful geometric object models such as generalized cylinder representations?

A survey of dextrous manipulation

technical reportThe development of mechanical end effectors capable of dextrous manipulation is a rapidly growing and quite successful field of research. It has in some sense put the focus on control issues, in particular, how to control these remarkably humanlike manipulators to perform the deft movement that we take for granted in the human hand. The kinematic and control issues surrounding manipulation research are clouded by more basic concerns such as: what is the goal of a manipulation system, is the anthropomorphic or functional design methodology appropriate, and to what degree does the control of the manipulator depend on other sensory systems. This paper examines the potential of creating a general purpose, anthropomorphically motivated, dextrous manipulation system. The discussion will focus on features of the human hand that permit its general usefulness as a manipulator. A survey of machinery designed to emulate these capabilities is presented. Finally, the tasks of grasping and manipulation are examined from the control standpoint to suggest a control paradigm which is descriptive, yet flexible and computationally efficient1

A control paradigm for general purpose manipulation systems

Journal ArticleMechanical end effectors capable of dextrous manipulation are now a reality. Solutions to the high level control issues, however, have so far proved difficult to formulate. We propose a methodology for control which produces the functionality required for a general purpose manipulation system. It is clear that the state of a hand/object system is a complex interaction between the geometry of the object, the character of the contact interaction, and the conditioning of the manipulator. The objective of this work is the creation of a framework within which constraints involving the manipulator, the object, and the hand/object interaction can be exploited to direct a goal oriented manipulation strategy. The set of contacts that are applied to a task can be partitioned into subsets with independent objectives. The individual contacts may then be driven over the interaction surface to improve the state of the grasp while the configuration of the hand addresses the application of required forces. A system of this sort is flexible enough to manage large numbers of contacts and to address manipulation tasks which require the removal and replacement of fingers in the grasp. A simulator has been constructed and results of its application to position synthesis for initial grasps is presented. A discussion of the manipulation testbed under construction at the University of Utah employing the Utah/MIT Dextrous hand is presented

Quantum time of flight distribution for cold trapped atoms

The time of flight distribution for a cloud of cold atoms falling freely under gravity is considered. We generalise the probability current density approach to calculate the quantum arrival time distribution for the mixed state describing the Maxwell-Boltzmann distribution of velocities for the falling atoms. We find an empirically testable difference between the time of flight distribution calculated using the quantum probability current and that obtained from a purely classical treatment which is usually employed in analysing time of flight measurements. The classical time of flight distribution matches with the quantum distribution in the large mass and high temperature limits.Comment: 6 pages, RevTex, 4 eps figure

Non-equilibrium dynamics of stochastic point processes with refractoriness

Stochastic point processes with refractoriness appear frequently in the quantitative analysis of physical and biological systems, such as the generation of action potentials by nerve cells, the release and reuptake of vesicles at a synapse, and the counting of particles by detector devices. Here we present an extension of renewal theory to describe ensembles of point processes with time varying input. This is made possible by a representation in terms of occupation numbers of two states: Active and refractory. The dynamics of these occupation numbers follows a distributed delay differential equation. In particular, our theory enables us to uncover the effect of refractoriness on the time-dependent rate of an ensemble of encoding point processes in response to modulation of the input. We present exact solutions that demonstrate generic features, such as stochastic transients and oscillations in the step response as well as resonances, phase jumps and frequency doubling in the transfer of periodic signals. We show that a large class of renewal processes can indeed be regarded as special cases of the model we analyze. Hence our approach represents a widely applicable framework to define and analyze non-stationary renewal processes.Comment: 8 pages, 4 figure

Spectrum and Charge Ratio of Vertical Cosmic Ray Muons up to Momenta of 2.5 TeV/c

The ALEPH detector at LEP has been used to measure the momentum spectrum and charge ratio of vertical cosmic ray muons underground. The sea-level cosmic ray muon spectrum for momenta up to 2.5 TeV/c has been obtained by correcting for the overburden of 320 meter water equivalent (mwe). The results are compared with Monte Carlo models for air shower development in the atmosphere. From the analysis of the spectrum the total flux and the spectral index of the cosmic ray primaries is inferred. The charge ratio suggests a dominantly light composition of cosmic ray primaries with energies up to 10^15 eV