Coupling of actin hydrolysis and polymerization: Reduced description with two nucleotide states

The polymerization of actin filaments is coupled to the hydrolysis of adenosine triphosphate (ATP), which involves both the cleavage of ATP and the release of inorganic phosphate. We describe hydrolysis by a reduced two-state model with a cooperative cleavage mechanism, where the cleavage rate depends on the state of the neighboring actin protomer in a filament. We obtain theoretical predictions of experimentally accessible steady state quantities such as the size of the ATP-actin cap, the size distribution of ATP-actin islands, and the cleavage flux for cooperative cleavage mechanisms.Comment: 6 page

Tomographic Reconstruction from a Few Views: A Multi-Marginal Optimal Transport Approach

19 pagesInternational audienceIn this article, we focus on tomographic reconstruction. The problem is to determine the shape of the interior interface using a tomographic approach while very few X-ray radiographs are performed. We use a multi-marginal optimal transport approach. Preliminary numerical results are presented

Control of the MKQA tuning and aperture kickers of the LHC

The large hadron collider (LHC) at CERN has been equipped with four fast pulsed kicker magnets in RA43 situated at point 4 which are part of the measurement system for the tune and the dynamic aperture of the LHC beam (Beam 1 and Beam 2). For the tune measurement 'Q', the magnets will excite oscillations in part of the beam. This is achieved by means of a generator producing a 5 µs base half-sine pulse of 1.2 kA [1] amplitude, superimposed with a 3rd harmonic to produce a 2 µs flat top. A kick repetition rate of 2 Hz will be possible. To measure the dynamic aperture 'A' of the LHC at different beam energies, the same magnets will also be driven by a more powerful generator which produces a 43 µs base half-sine current pulse of 3.8 kA. For the 'A' mode a thyristor is used as switching element inside the generator. A final third mode named 'AC dipole' will rely on the beam being excited coherently at a frequency close but outside its Eigen-frequencies by an oscillating dipole field. The beam is expected to oscillate at the exciter frequency of 3 kHz with a phase shift of π/2. The 'AC dipole' will use two 18 kW audio amplifiers capable of driving the magnets at 1 kHz(rms) around 3 kHz or between 2.7 kHz and 4 kHz. The complete system uses supervisory control implemented with Siemens PLC technology with added Siemens PROFIsafe safety feature to treat the various interlocks that have been introduced in the circuits and to assu re a safe functioning and provide 'LOCAL' and 'REMOTE' control (via CCC) of the complete installation

Protection of the LHC against Unsynchronised Beam Aborts

An unsynchronised beam abort in the LHC could damage downstream accelerator components, in particular the extraction septum magnets, the experimental low-beta triplet magnet apertures and the tertiary collimators. Although the LHC beam dumping system includes design features to minimise their frequency, such unsynchronised aborts cannot be excluded. A system of protection devices comprising fixed and moveable diluters and collimators will protect the downstream LHC aperture from the misdirected bunches in case of such a failure. The sources of unsynchronised aborts are described, together with the requirements and design of the protection devices and their expected performance. The accompanying operational requirements and envisaged solutions are discussed, in particular the problem of ensuring the local orbit at the protection devices

Automatic conditioning of the LHC injection kickers

The LHC injection systems, located near the interaction regions 2 and 8, comprise 4 fast pulsed kicker magnets (MKI) per ring to bring the beam onto the orbit. Each magnet is housed in a separate vacuum tank. Their nominal operating voltage is 54 kV, and the nominal pulse length 7.86 µs. To prepare these magnets for operation they are once assembled and baked out, gradually subjected to higher and higher voltages and greater pulse lengths, until their voltage holding capability is sufficiently beyond the nominal operating conditions. In the past this "conditioning" was carried out manually, and thus a manpower-intensive, and also technically not optimal procedure. To overcome these drawbacks a program has been developed, running in a Programmable Logic Controller (PLC), which has been used to condition the full suite of LHC injection kickers automatically

The Low-Level Control System for the CERN PS Multi-Turn Extraction Kickers

To reduce the beam losses when preparing high intensity proton beam for the CERN Neutrino to Gran Sasso (CNGS) facility, a new Multi-Turn extraction (MTE) scheme has been implemented in the PS, to replace the present Continuous Transfer (CT) to the SPS. Industrial off-the-shelf components have been used for the low-level part of the MTE kicker control system. National Instruments PXI systems are used to control the high voltage pulse generators and a SIEMENS programmable logic controller (PLC) handles the centralised oil cooling and gas insulation sub-system

A Framework for Decision-based Consistencies

International audienceConsistencies are properties of constraint networks that can be enforced by appropriate algorithms to reduce the size of the search space to be explored. Recently, many consistencies built upon taking decisions (most often, variable assignments) and stronger than (general- ized) arc consistency have been introduced. In this paper, our ambition is to present a clear picture of decision-based consistencies. We identify four general classes (or levels) of decision-based consistencies, denoted by S∆φ, E∆φ, B∆φ and D∆φ, study their relationships, and show that known consistencies are particular cases of these classes. Interestingly, this gen- eral framework provides us with a better insight into decision-based con- sistencies, and allows us to derive many new consistencies that can be directly integrated and compared with other ones