A multimodality investigation of cerebral hemodynamics and autoregulation in pharmacological MRI

Pharmacological MRI (phMRI) methods have been widely applied to assess the central hemodynamic response to pharmacological intervention as a surrogate for changes in the underlying neuronal activity. However, many psychoactive drugs can also affect cardiovascular parameters, including arterial blood pressure (BP). Abrupt changes in BP or the anesthetic agents used in preclinical phMRI may impair cerebral blood flow (CBF) autoregulation mechanisms, potentially introducing confounds in the phMRI response. Moreover, relative cerebral blood volume (rCBV), often measured in small-animal phMRI studies, may be sensitive to BP changes even in the presence of intact autoregulation. We applied laser Doppler flowmetry and MRI to measure changes in CBF and microvascular CBV induced by increasing doses of intravenous norepinephrine (NE) challenge in the halothane-anesthetized rat. NE is a potent vasopressor that does not cross the blood-brain barrier and mimics the rapid BP changes typically observed with acute drug challenges. We found that CBF autoregulation was maintained over a BP range of 60-120 mmHg. Under these conditions, no significant central rCBV responses were observed, suggesting that microvascular rCBV changes in response to abrupt changes in perfusion pressure are negligible within the autoregulatory range. Larger BP responses were accompanied by significant changes in both CBV and CBF that might confound the interpretation of phMRI results.     

Detection loophole in asymmetric bell experiments

The problem of closing the detection loophole with asymmetric systems, such as entangled atom-photon pairs, is addressed. We show that, for the Bell inequality I3322, a minimal detection efficiency of 43% can be tolerated for one of the particles, if the other one is always detected. We also study the influence of noise and discuss the prospects of experimental implementation.     

The racemate cage. Influence of p(1),n(1) salt occurrence on enantiomer separation processes. The case of trans-chrysanthemic acid

The occurrence of p(1),n(1) salt when accompanied by substrate self-association can have profound effects on enantiomer separation processes of non-racemic mixtures, impeding the complete recovery of the major enantiomer through formation of an inescapable racemate cage.     

Cohomological construction of relative twists

Let g be a complex, semi-simple Lie algebra, h⊂g a Cartan subalgebra and D a subdiagram of the Dynkin diagram of g. Let gD⊂lD⊆g be the corresponding semi-simple and Levi subalgebras and consider two invariant solutions Φ∈g(Ug⊗3???) and of the pentagon equation for g and gD respectively. Motivated by the theory of quasi-Coxeter quasitriangular quasibialgebras [V. Toledano Laredo, Quasi-Coxeter algebras, Dynkin diagram cohomology and quantum Weyl groups, math.QA/0506529], we study in this paper the existence of a relative twist, that is an element F∈lD(Ug⊗2???) such that the twist of Φ by F is ΦD. Adapting the method of Donin and Shnider [J. Donin, S. Shnider, Cohomological construction of quantized universal enveloping algebras, Trans. Amer. Math. Soc. 349 (1997) 1611-1632], who treated the case of an empty D, so that lD=h and ΦD=¹⊗3, we give a cohomological construction of such an F under the assumption that ΦD is the image of Φ under the generalised Harish-Chandra homomorphism . We also show that F is unique up to a gauge transformation if lD is of corank 1 or F satisfies FΘ=F²¹ where Θ∈Aut(g) is an involution acting as −1 on h.     

Comparison of kinetic and continuum approaches for simulation of shock wave/boundary layer interaction

The present paper, which is a collaboration between three different research groups, analyzes the efficiency of various numerical approaches to describe the complex problem of shock wave/boundary layer interaction. Computations were carried out based on a kinetic approach (Direct Simulation Monte Carlo method) and on two continuum approaches (Navier-Stokes equations and quasigasdynamic equations), which are validated by comparison with experimental results obtained in the R5Ch blowdown Hypersonic Wind Tunnel in ONERA. The influence of the slip boundary conditions for two continuum approaches are also studied. The results obtained by all models display the good prediction of the main structure of the flow and the levels of the flux coefficients are very close to those measured. The implementation of the slip boundary condition for the continuum approaches improves the agreement with the experimental data. Received 12 July 2001 / Accepted 24 May 2002 /Published online 4 December 2002 Correspondence to: D. Zeitoun (e-mail: David.Zeitoun@polytech.univ-mrs.fr) An abridged version of this paper was presented at the 23rd Int. Symposium on Shock Waves at Fort Worth, Texas, from July 22 to 27, 2001     

On the convergence rate of a cusp-corrected damped multipole expansion for the second-order H-H+ induction energy

The improvement in the convergence rate of the damped multipole expansion for the second order H-H⁺ induction energy due to the inclusion into the first-order function of a term satisfying the electron-proton cusp condition is quantitatively investigated. Following a technique suggested by Schwartz, the multipole contributions to the energy are put in the form of series ordered by inverse powers of the quantum number l. It is shown that, for high values of l, the dependence of the leading terms is raised from l ^-4 to l ^-6 by the cusp correction.     

Methylene blue as an electrochemical indicator for DF508 cystic fibrosis mutation detection

Cystic fibrosis is one of the most common life-shortening, childhood-onset inherited diseases. Among the 1,000 known cystic fibrosis-related mutations, DF508 is the most common, with a frequency varying between 50% and 70% according to geographical areas and population typology. In this work, we report the use of methylene blue as an electrochemical reporting agent in the discrimination of synthetic PCR analogue of the DF508 cystic fibrosis mutation (Mut) from the wild type (Wt). At optimum experimental condition, a discrimination factor between mutant and wild type of approximately 1.5-fold was found. The proposed assay was quantitative and linear in the range of 10–100 nM, exhibiting a limit of detection of 2.64 nM. Electrochemical studies at variable ionic strength conditions allowed further elucidation of the mechanism of the methylene blue (MB)–DNA interaction. To the best of our knowledge, this is the first report of detection of hybridisation solely via guanine-specific MB–DNA interaction simultaneously in MB solution, independent of electrostatic interaction as demonstrated in the ionic strength study. The introduction of formamide in the hybridization buffer, to improve discrimination, was also investigated. Finally, mutant wild type discrimination was demonstrated, at 10 nM concentration, with the use of a multi-sensor setup.     

Reduced dipole pseudospectra for the accurate tabulation of C6 dispersion coefficients

The possibility of tabulating accurate reduced dipole pseudospectra of single molecules is of great importance for obtaining reliable dipole dispersion constants from which C₆ dispersion coefficients can be derived for all possible interacting pairs. Use of an efficient interpolation procedure allows to obtain dispersion constants from analytical integration of the Casimir–Polder integral over the product of frequency-dependent polarizabilities (FDPs) at imaginary frequencies. FDP calculations can then be done at a few selected frequencies, so overcoming at a time the difficulties arising from numerical quadratures and sensibly reducing the computational demand. In the static case, appropriately reduced n-term pseudospectra are obtained by forcing in an optimal way large N-term extended pseudospectra to be converted to FDPs using the same interpolation technique. Calculations performed at the eight frequencies arising by choosing n = 4 (four-term approximation) in the optimized interpolation procedure, give reduced dipole pseudospectra from which isotropic C₆ dispersion coefficients and γ₆ anisotropy coefficients are obtained in almost perfect agreement with the result of the most accurate data available from the literature and of recently proposed variational techniques.