Uniform boundedness of the inverse of a Jacobian matrix arising in regularized interior-point methods

This short communication analyses a boundedness property of the inverse of a Jacobian matrix that arises in regularized primal-dual interior-point methods for linear and nonlinear programming. This result should be a useful tool for the convergence analysis of these kinds of methods.     

Acousto-optic light deflection in an Al2O3 optical waveguide structure

The total deflection of an optical guided wave by a surface acoustic wave (SAW) in a silicon-based SiO₂/AL₂O₃/SiO₂ optical waveguide structure is reported. The SAW is generated by an interdigital transducer with piezoelectric ZnO deposited on top of the optical waveguide structure.     

Repeated Quantum Non-Demolition Measurements: Convergence and Continuous Time Limit

We analyze general enough models of repeated indirect measurements in which a quantum system interacts repeatedly with randomly chosen probes on which von Neumann direct measurements are performed. We prove, under suitable hypotheses, that the system state probability distribution converges after a large number of repeated indirect measurements, in a way compatible with quantum wave function collapse. We extend this result to mixed states and we prove similar results for the system density matrix. We show that the convergence is exponential with a rate given by some relevant mean relative entropies. We also prove that, under appropriate rescaling of the system and probe interactions, the state probability distribution and the system density matrix are solutions of stochastic differential equations modeling continuous-time quantum measurements. We analyze the large time behavior of these continuous time processes and prove convergence.     

Detection of 28 neurotransmitters and related compounds in biological fluids by liquid chromatography/tandem mass spectrometry

This work presents two liquid chromatography/tandem mass spectrometry (LC/MS/MS) acquisition modes: multiple reaction monitoring (MRM) and neutral loss scan (NL), for the analysis of 28 compounds in a mixture. This mixture includes 21 compounds related to the metabolism of three amino acids: tyrosine, tryptophan and glutamic acid, two pterins and five deuterated compounds used as internal standards. The identification of compounds is achieved using the retention times (RT) and the characteristic fragmentations of ionized compounds. The acquisition modes used for the detection of characteristic ions turned out to be complementary: the identification of expected compounds only is feasible by MRM while expected and unexpected compounds are detected by NL. In the first part of this work, the fragmentations characterizing each molecule of interest are described. These fragmentations are used in the second part for the detection by MRM and NL of selected compounds in mixture with and without biological fluids. Any preliminary extraction precedes the analysis of compounds in biological fluids.     

Charge order, metallic behavior, and superconductivity in La2-xBaxCuO4 with x=1/8

The ab-plane optical properties of a cleaved single crystal of La2-xBaxCuO4 for x=1/8 (Tc approximately =2.4 K) have been measured over a wide frequency and temperature range. The low-frequency conductivity is Drude-like and shows a metallic response with decreasing temperature. However, below approximately =60 K, corresponding to the onset of charge-stripe order, there is a rapid loss of spectral weight below about 40 meV. The behavior is quite different from that typically associated with the pseudogap in the normal state of the cuprates. Instead, the gapping of the normal-state single-particle excitations looks surprisingly similar to that observed in superconducting La2-xSrxCuO4, including the presence of a residual Drude peak with reduced weight.     

Local path-following property of inexact interior methods in nonlinear programming

We study the local behavior of a primal-dual inexact interior point methods for solving nonlinear systems arising from the solution of nonlinear optimization problems or more generally from nonlinear complementarity problems. The algorithm is based on the Newton method applied to a sequence of perturbed systems that follows by perturbation of the complementarity equations of the original system. In case of an exact solution of the Newton system, it has been shown that the sequence of iterates is asymptotically tangent to the central path (Armand and Benoist in Math. Program. 115:199?C222, 2008). The purpose of the present paper is to extend this result to an inexact solution of the Newton system. We give quite general conditions on the different parameters of the algorithm, so that this asymptotic property is satisfied. Some numerical tests are reported to illustrate our theoretical results.     

Effects of manganese injected into rat nostrils: implications for in vivo functional study of olfaction using MEMRI

Manganese-enhanced magnetic resonance imaging (MEMRI) is a powerful tool for visualizing neuronal pathways and mapping brain activity modulation. A potential drawback of MEMRI lies in the toxic effects of manganese (Mn), which also depend on its administration route. The aim of this study was to analyze the effects of Mn doses injected into the nostrils of rats on both olfactory perception and MRI contrast enhancement. For this purpose, doses in the range 0-8 μmol MnCl₂ were tested. Behavioral items were quantified with and without odor stimulation during the first 2 h following Mn injection. The MRI study was performed after 16 h of intermittent olfactory stimulations. Behavioral results showed that, during the early period following Mn administration, spontaneous motor activity was not affected, while odor-related behaviors were dose-dependently reduced. MRI results showed that, in the primary olfactory cortex, contrast was rapidly enhanced for Mn doses up to 0.3 μmol and very slowly above. This dose of 0.3 μmol Mn can thus be taken as the optimal dose for injection into rat nostrils to ensure a reproducible contrast in MRI studies while sparing olfactory perception.     

Measurement of an exceptionally weak electron-phonon coupling on the surface of the topological insulator Bi2Se3 using angle-resolved photoemission spectroscopy

Gapless surface states on topological insulators are protected from elastic scattering on nonmagnetic impurities which makes them promising candidates for low-power electronic applications. However, for widespread applications, these states should have to remain coherent at ambient temperatures. Here, we studied temperature dependence of the electronic structure and the scattering rates on the surface of a model topological insulator, Bi2Se3, by high-resolution angle-resolved photoemission spectroscopy. We found an extremely weak broadening of the topological surface state with temperature and no anomalies in the state's dispersion, indicating exceptionally weak electron-phonon coupling. Our results demonstrate that the topological surface state is protected not only from elastic scattering on impurities, but also from scattering on low-energy phonons, suggesting that topological insulators could serve as a basis for room-temperature electronic devices.     

Photoemission spectroscopy of magnetic and nonmagnetic impurities on the surface of the Bi2Se3 topological insulator

Dirac-like surface states on surfaces of topological insulators have a chiral spin structure that suppresses backscattering and protects the coherence of these states in the presence of nonmagnetic scatterers. In contrast, magnetic scatterers should open the backscattering channel via the spin-flip processes and degrade the state's coherence. We present angle-resolved photoemission spectroscopy studies of the electronic structure and the scattering rates upon the adsorption of various magnetic and nonmagnetic impurities on the surface of Bi2Se3, a model topological insulator. We reveal a remarkable insensitivity of the topological surface state to both nonmagnetic and magnetic impurities in the low impurity concentration regime. Scattering channels open up with the emergence of hexagonal warping in the high-doping regime, irrespective of the impurity's magnetic moment.