Speedy motions of a body immersed in an infinitely extended medium

We study the motion of a classical point body of mass M, moving under the action of a constant force of intensity E and immersed in a Vlasov fluid of free particles, interacting with the body via a bounded short range potential Psi. We prove that if its initial velocity is large enough then the body escapes to infinity increasing its speed without any bound "runaway effect". Moreover, the body asymptotically reaches a uniformly accelerated motion with acceleration E/M. We then discuss at a heuristic level the case in which Psi(r) diverges at short distances like g r^{-a}, g,a>0, by showing that the runaway effect still occurs if a<2.Comment: 15 page

On the propagation of a perturbation in an anharmonic system

We give a not trivial upper bound on the velocity of disturbances in an infinitely extended anharmonic system at thermal equilibrium. The proof is achieved by combining a control on the non equilibrium dynamics with an explicit use of the state invariance with respect to the time evolution.Comment: 14 page

Cucker–Smale Type Dynamics of Infinitely Many Individuals with Repulsive Forces

We study the existence and uniqueness of the time evolution of a system of infinitely many individuals, moving in a tunnel and subjected to a Cucker–Smale type alignment dynamics with compactly supported communication kernels and to short-range repulsive interactions to avoid collisions

2-D constrained Navier-Stokes equation and intermediate asymptotics

We introduce a modified version of the two-dimensional Navier-Stokes equation, preserving energy and momentum of inertia, which is motivated by the occurrence of different dissipation time scales and related to the gradient flow structure of the 2-D Navier-Stokes equation. The hope is to understand intermediate asymptotics. The analysis we present here is purely formal. A rigorous study of this equation will be done in a forthcoming paper

The GBT: A proposed architecure for multi-Gb/s data transmission in high energy physics

The future upgrade of the LHC accelerator, the SLHC, will increase the beam luminosity by a factor of ten leading to a corresponding growth of the amounts of data to be treated by the data transmission and acquisition systems. The development of the GBT chipset addresses this issue providing a means to increase the bandwidth available to transmit data to and from the counting room. The GigaBit Transceiver (GBT) architecture will provide the support to transmit simultaneously the three types of information required to run an experiment in a hostile radiation environment over a multipurpose link. This paper describes the GBT link architecture and some aspects of its implementation. As this project is still in the specification phase, detailed features might change prior to the final silicon fabrication

An 80 Mbit/s radiation-tolerant optical receiver for the CMS digital optical link

The CMS tracker slow control system will use approximately 1000 digital optical links for the transmission of timing, trigger and control signals. In this system, the 80 Mbit/s optical receiver at the detector end of each optical link has to be radiation hard since it will operate in the severe radiation environment of the CMS tracker (10 Mrad in 10 years). We have developed a prototype circuit in a 0.25 mu m commercial CMOS process using radiation tolerant layout practices to achieve the required radiation tolerance. This effective technique consists in the systematic use of enclosed (edgeless) NMOS transistors and guardrings, and relies in the natural total dose hardness of the thin gate oxide of deep submicron processes. The circuit features an automatic gain control loop allowing detection of wide dynamic range input signals (-20 to -3 d Bm) with minimum noise, compatible with the maximum expected radiation-induced drop in quantum efficiency of the PIN photodiode. A second feedback loop compensates a photodiode leakage current up to 100 mu A, and the circuit outputs an LVDS signal. Four receiver channels were integrated in a 2*2 mm/sup 2/ chip, out of which two were simultaneously bonded to two PIN photodiodes, and their BER performance was measured before and after an irradiation with 10 keV X-rays up to 20 Mrad (SiO/sub 2/). (11 refs)