How to handle the inelastic collapse of a dissipative hard-sphere gas with the TC model

The inelastic hard sphere model of granular material is simple, easily accessible to theory and simulation, and captures much of the physics of granular media. It has three drawbacks, all related to the approximation that collisions are instantaneous: 1) The number of collisions per unit time can diverge, i.e. the ``inelastic collapse'' can occur. 2) All interactions are binary, multiparticle contacts cannot occur and 3) no static limit exists. We extend the inelastic hard sphere model by defining a duration of contact t_c such that dissipation is allowed only if the time between contacts is larger than t_c. We name this generalized model the ``TC model'' and discuss it using examples of dynamic and static systems. The contact duration used here does not change the instantaneous nature of the hard sphere contacts, but accounts for a reduced dissipation during ``multiparticle contacts''. Kinetic and elastic energies are defined as well as forces and stresses in the system. Finally, we present event-driven numerical simulations of situations far beyond the inelastic collapse, possible only with the TC model.Comment: 15 pages, Latex, 14 bw.ps figures + 2 col.ps figures, to be published in Granular Matter 1(3) 199

An Spectrometer for Investigating the Spectral Momentum Density of Thin Films

An (e, 2e) spectrometer has been constructed for detecting scattered and recoiling electrons from a thin solid film. The cross section for observing the two electrons in coincidence is proportional to the spectral momentum density of the target. In this spectrometer the energy of the incident electron beam is 25 keV and the beam current is approximately 40 μA. The energy resolution (FWHM) is ≤4 eV. The momentum resolution (FWHM) can be varied from 0.2 to 1.0 Å−1. Preliminary coincidence data from an amorphous carbon film are presented

A facility to Search for Hidden Particles (SHiP) at the CERN SPS

A new general purpose fixed target facility is proposed at the CERN SPS accelerator which is aimed at exploring the domain of hidden particles and make measurements with tau neutrinos. Hidden particles are predicted by a large number of models beyond the Standard Model. The high intensity of the SPS 400~GeV beam allows probing a wide variety of models containing light long-lived exotic particles with masses below ${\cal O}$(10)~GeV/c$^2$, including very weakly interacting low-energy SUSY states. The experimental programme of the proposed facility is capable of being extended in the future, e.g. to include direct searches for Dark Matter and Lepton Flavour Violation.Comment: Technical Proposa

Pcm telemtry- a new approach using all- magnetic techniques

Digital all-magnetic circuit technique used in pulse code modulation telemetry system

Development of the detector control system for the COMPASS detector at CERN

This document describes the implementation of system control software for the COMPASS experiment at CERN. This work concentrates on the GEM and silicon detectors, but it also includes parts that are generally useful for all kinds of detectors. The only prerequisites were the PVSS II SCADA-system and the JCOP PVSS framework distributed by ITCO at CERN. To achieve the given aims there was work to do both on a C++ framework called SLiC for hardware access and on top of the JCOP framework to customise it for the special needs of the GEM and silicon detectors

A study of Radiation-Tolerant Voltage-Controlled Oscillators designs in 65 nm bulk and 28 nm FDSOI CMOS technologies

Phase-locked loop (PLL) systems are widely employed in integrated circuits for space analog devices and communications systems that operate in radiation environments, where significant perturbations, especially in terms of phase noise, can be generated due to radiation particles. Among all the blocks that form a PLL system, previous research suggests the voltage-controlled oscillator (VCO) is one of the most critical components in terms of radiation tolerance and electric performance. Ring oscillators (ROs) and LC-tank VCOs have been commonly employed in high-performance PLLs. Nevertheless, both structures have drawbacks including a limited tuning range, high sensitivity to phase noise, limited radiation tolerance, and large design areas. In order to fulfill these high-performance requirements, a current-model logic (CML) based RO-VCO is presented as a possible solution capable of reducing the limitations of the commonly used structures and exploiting their advantages. The proposed hybrid VCO model includes passive components in its design which are the key parameters that define oscillation frequency of this structure. This tunable oscillator has been designed and tested in 65nm Bulk and 28 nm Fully depleted silicon-on-insulator (FDSOI) CMOS technologies The 65nm testchip was designed to compare the behavior of the proposed CML VCO with a current-starved RO and a radiation hardened by design (RHBD) LC-tank VCO in terms of tuning range, phase noise, Single event effect (SEE) sensitivity and design area. Simulations were carried out by applying a double exponential current pulse into different sensitive nodes of the three VCOs. In addition, SEE tests were conducted using pulsed laser experiments. Simulation and test results show that a CML VCO can effectively overcome the limitations presented by a RO-VCO and LC-tank VCO, achieving a wide range of tuning, and low sensitivity to noise and SEEs without the need for a large cross-section. Further studies of the proposed CML VCO were done on 28nm FDSOI in order to reduce the leakage current and increase the switching speed. the same current-starved VCO and CML VCO were implemented on this testchip, and simulations were performed by injecting a double exponential current pulse energy into the previously defined sensitive nodes. The results show SEE sensitivity improvement without narrowing the tuning range or affecting the phase noise response

Hardware and Software Studies for the Alignment of the Proton CT

Proton therapy is a form of particle therapy using protons to irradiate tumors as a form of cancer treatment. It is becoming more and more popular around the world, including in Norway. To locate the tumor, conventional CT scan is used today, which uses x-ray beams. The proton energy deposition is then achieved by conversions that are not optimal. Proton computed tomography has several important advantages over the conventional computed tomography. The two main advantages are giving a lower dose to the patient during imaging compared to the conventional method and eliminating the need for conversion of photon attenuation to stopping power for protons, which is a source of error. This is necessary in particle therapy, because the physical properties of photons and protons are very different. Using the same type of particles for both imaging and therapy will potentially increase the accuracy of particle therapy treatment plans. For proton CT to be possible, the detectors need to accurately detect the proton tracks and energy depositions and for that the layers of the proton detectors have to be aligned. This master's thesis is an attempt at finding a method for the purpose of alignment in a proton CT detector.Masteroppgave i medisinsk teknologiMTEK39