Complexity of control on finite automata

We consider control questions for finite automata viewed as input/output systems. In particular, we find estimates of the minimal number of states of an automaton able to control a given automaton. We prove that, on average, feedback closed-loop control automata do not have fewer states than open-loop control automata when the control objective is to steer the controlled automaton to a target state. We compare our approach to other ways of formalizing of formalizing analogous control objectives.     

Destabilizing interactions between the partners of a bifunctional fusion protein

Hybrid MalE–GVP is a bifunctional protein in vitro sinceit binds maltose as protein MalE of Escherichia coli and sinceit is dimeric and specifically binds single-stranded DNA asprotein GVP of phage M13. The oxidation rate of a unique cysteineresidue was used to compare the stabilities of GVP in its freeand hybrid forms, under conditions where MalE was either foldedor unfolded by a denaturing agent. The results showed that boththe covalent link and tertiary non-covalent interactions betweenMalE and GVP destabilized GVP in MalE–GVP. To test whetherGVP had identical structures in its free and hybrid forms, mutationswere used as local conformational probes. The effects of thesemutations on the capabilities of MalE–GVP to dimerizeand to bind single-stranded DNA were assayed in vitro. Theywere compatible with the effects of the same mutations on theglobal activity of free GVP in vivo and with the effects thatcould be predicted from the known data on free GVP, in particularits crystal structure. Thus, one partner of a hybrid proteincan be destabilized by the other partner while maintaining itsstructural and functional characteristics.     

Fast computation of minimal elementary decompositions of metabolic flux vectors

The concept of elementary flux vector is valuable in a number of applications of metabolic engineering. For instance, in metabolic flux analysis, each admissible flux vector can be expressed as a non-negative linear combination of a small number of elementary flux vectors. However a critical issue concerns the total number of elementary flux vectors which may be huge because it combinatorially increases with the size of the metabolic network. In this paper we present a fast algorithm that randomly computes a decomposition of admissible flux vectors in a minimal number of elementary flux vectors without explicitly enumerating all of them.     

Investigation of 3-D mechanical properties of blood vessels using a new in vitro tests system: results on sheep common carotid arteries

In order to investigate the three-dimensional (3-D) mechanical properties of blood vessels, a new experimental device is described allowing in vitro static and dynamic measurements on segments of arteries with high technical performances. Static tests are applied to sheep common carotid arteries. Considering a thick-walled cylindrical model of orthotropic material under large deformations, a classical 3-D approach based on strain energy density is used to calculate the resulting mechanical behavior law in radial and circumferencial directions and stresses distribution throughout the wall thickness. Results are presented with reference to unloaded and zero-stress initial state thanks to simple measurements of inner and outer circumferences. A particular ratio relating the two main stresses (circumferential and longitudinal) is calculated that put into the forth the progressive modifications in the direction of the predominant stress in the wall and the specific radial location where these changes occur. The authors observe that this point location is a function of the test conditions of the specimen, i.e., stretching length and level of pressure     

Achievable budget improvement with Raman amplification and remotelypumped postamplification at transmit side of 622 Mbit/s and 2.5 Gbit/srepeaterless systems

This paper investigates Raman amplification and remotely pumped postamplification in repeaterless systems based on standard fiber. Design rules taking into account self phase modulation are presented along with the achievable power budget improvements     

Passive Q-switching in all-fibre Raman laser with distributed Rayleigh feedback

The experimental demonstration of the all-fibre passive Q-switching operation of a Raman fibre laser is reported. Giant pulses around 1550 nm with a peak power of 1 kW and pulse duration down to 1 ns were obtained with a 10 km-long fibre cavity pumped by a 2.4 W continuous-wave fibre laser source. Reported experimental data indicate that Rayleigh, Brillouin and Raman scatterings are all involved in the pulse generation process.     

Medical certificate of neonatal death]

A specific neonatal death certificate has been put into use in France since April 1997. It must be completed for any infants born alive and deceased between 0 and 27 days. Its content is presented together with the results of an evaluation of its use performed during a 3 month period in 1996. This certificate is aimed to improve the mortality statistics of the neonatal period, thus helping to better define the priorities in the medical care and prevention fields.     

The Lyapunov exponent and joint spectral radius of pairs of matrices are hard—when not impossible—to compute and to approximate

We analyze the computability and the complexity of various definitions of spectral radii for sets of matrices. We show that the joint and generalized spectral radii of two integer matrices are not approximable in polynomial time, and that two related quantities—the lower spectral radius and the largest Lyapunov exponent—are not algorithmically approximable.This work was completed while Blondel was visiting Tsitsiklis at MIT. This research was supported by the ARO under Grant DAAL-03-92-G-0115.     

A sufficient condition for simultaneous stabilization

The condition under which it is possible to find a single controller that stabilizes k single-input single-output linear time-invariant systems p_i(s) (i=1,. . .,k) is investigated. The concept of avoidance in the complex plane is introduced and used to derive a sufficient condition for k systems to be simultaneously stabilizable. A method for constructing a simultaneous stabilizing controller is also provided and is illustrated by an example