Neural activity associated with distinguishing concurrent auditory objects

The neural processes underlying concurrent sound segregation were examined by using event-related brain potentials. Participants were presented with complex sounds comprised of multiple harmonics, one of which could be mistuned so that it was no longer an integer multiple of the fundamental. In separate blocks of trials, short-, middle-, and long-duration sounds were presented and participants indicated whether they heard one sound (i.e., buzz) or two sounds (i.e., buzz plus another sound with a pure-tone quality). The auditory stimuli were also presented while participants watched a silent movie in order to evaluate the extent to which the mistuned harmonic could be automatically detected. The perception of the mistuned harmonic as a separate sound was associated with a biphasic negative-positive potential that peaked at about 150 and 350 ms after sound onset, respectively. Long duration sounds also elicited a sustained potential that was greater in amplitude when the mistuned harmonic was perceptually segregated from the complex sound. The early negative wave, referred to as the object-related negativity (ORN), was present during both active and passive listening, whereas the positive wave and the mistuning-related changes in sustained potentials were present only when participants attended to the stimuli. These results are consistent with a two-stage model of auditory scene analysis in which the acoustic wave is automatically decomposed into perceptual groups that can be identified by higher executive functions. The ORN and the positive waves were little affected by sound duration, indicating that concurrent sound segregation depends on transient neural responses elicited by the discrepancy between the mistuned harmonic and the harmonic frequency expected based on the fundamental frequency of the incoming stimulus.     

Rotational Analysis of the ΔvSiH=3-6 Stretching Vibrational Overtones of HSiD3

The nν₁ SiH stretching overtone transitions of trideuterosilane, HSiD₃, have been recorded by Fourier transform spectroscopy (n=3 and 4) and by intracavity laser absorption spectroscopy (n=5 and 6). The unusually weak 3ν₁ band is affected by considerable intensity and energy perturbations. The 4ν₁ band is also strongly perturbed but the interaction with the dark states is more limited and part of the rotational structure of the v₁=4 upper state could be satisfactorily modeled. Less pronounced perturbations affect the v₁=5 level, newly detected by ICLAS. Its rotational structure is locally perturbed by anharmonic coupling with an unidentified vibrational dark state. The global modeling of the interacting dyad allowed the determination of the perturber parameters and the assignment of extra lines due to an intensity transfer from the v₁=5 bright state to the dark state. In agreement with a previous ICLAS study, the 6ν₁ band near 12 113 cm⁻¹ was found free of perturbation. About six hundred line positions could be reproduced with an rms of 4.6×10⁻³ cm⁻¹, leading to a significantly improved set of rovibrational parameters. The striking evolution of the rotational structure, which exhibits fewer and fewer perturbations when the SiH excitation increases, is discussed.     

On Quantum Phase Transition. II. The Falicov–Kimball Model

The Falicov–Kimball (FK) model⁽¹⁾ involves two types of interacting particles: first the itinerant spinless electrons are quantum particles, secondly the static ions are classical particles. It is striking to see that, despite the simplicity of its hamiltonian, the phase diagram of the FK model is highly sophisticated, moreover it remains in great part conjectural. An antiferromagnetic phase transition was proven for the FK model on a square lattice in the seminal paper of T. Kennedy and E. Lieb.⁽²⁾ This result was extended by Lebowitz and Macris⁽³⁾ to small magnetic field. Then the same result was obtained by using a new method.⁽⁴⁾ The main results of this paper concerns the two dimensional FK model on a square lattice, for which we apply the general results contained in ref. 5. First there exists an effective hamiltonian which is a long range many body Ising model, and which governs the behaviour of the ions. Secondly we compute explicitly the truncated effective hamiltonian up to the fourth order w.r.t. a small parameter (the inverse of the on site energy). Finally we use the classical Pirogov–Sinai theory, to get the hierarchy of the phase diagrams up to the fourth order. More precisely, we show that, when the chemical potential varies, the FK model exhibits, at low temperature, a sequence of phase transitions: first between phases of period two, then of period three, then of period four, and finally of period five. In each case the completeness of the phase diagram is proved. This paper supports the conjecture that the phase diagram of the FK model contains periodic phases outside of a Cantor set.     

Macrotricyclic quaternary tetraammonium receptors: halide anion recognition and interfacial activity at an aqueous interface. A molecular dynamics investigation

We report a molecular dynamics study of the halide inclusion complexes X(-) subset L(4+) of a macrotricyclic tetrahedral receptor L(4+) built from four quaternary ammonium sites connected by six (CH(2))(n) chains. The hydrophilic/hydrophobic character of the complexes is investigated at a water/chloroform interface, represented explicitly and, despite their +3 charge and "spherical" shape, they are found to display amphiphilic behavior and to concentrate at the interface. The more lipophilic N-substituted CH(2)phi derivative, as well as less charged models are more surface active than the N-Me substituted host. In relation with the Hofmeister series, I(-) exo neutralizing counterions are compared with Cl(-) anions and are found to sit closer to the interface, which becomes more neutral. The "macrocyclic interfacial effect" is investigated by a comparison of L(4+) complexes with their acyclic counterparts. Finally, we address the question of anion binding selectivity by L(4+) and its L(1) (4+) and L(2) (4+) topological isomers. F(-) is too small for these three hosts, while I(-) is too big. According to free energy perturbation calculations, Cl(-) is preferred to Br(-), but somewhat more by L(1) (4+) than by L(4+).     

Dynamic behavior in diplatinum metalloreceptors

Diplatinum metalloreceptors anti-4a and anti-4b exhibit dynamic behavior in solution that is modified by anion binding. An X-ray crystal structure determination of anti-4a supports its proposed solution structure.     

Spin densities in a ferromagnetic bimetallic chain compound: polarized neutron diffraction and DFT calculations

The spin population distribution in the ferromagnetically coupled hetero-bimetallic chain compound [MnNi(NO(2))(4)(en)(2)] (en = 1,2-ethanediamine) has been investigated by means of polarized neutron diffraction experiments, and the results compared with those from theoretical estimates obtained via calculations based on density functional theory on dinuclear molecular models of the chain. The spin distributions obtained from experiment and from theory are consistent and reflect a larger spin delocalization from the Ni atom due to the more covalent character of the Ni-N bonds compared to the Mn-O ones. Also a nearly isotropic spin distribution is observed for the more ionic d(5) Mn(2+) ion and a clearly anisotropic distribution for the d(8) Ni(2+) ion. The use of dinuclear molecular models for the calculation of the exchange coupling constant between Ni and Mn provide upper and lower limits (+17.6 and -4.2 cm(-)(1)) for the experimentally determined value (+1.3 cm(-)(1)), depending on how the missing part of the chain is simulated, but yield essentially the same spin distribution. The Mn(II)-Ni(II) weak ferromagnetic coupling in the chain is interpreted in a spin delocalization mechanism as resulting from the weakness of the overlap between the magnetic orbitals centered on nickel and those centered on manganese which are only weakly delocalized on the ligands.     

Estimation and correction of matrix effects in gas chromatographic pesticide multiresidue analytical methods with a nitrogen-phosphorus detector

The assessment of matrix effects in the quantification of organophosphorus pesticides in fruit and vegetables by GC-NPD, were studied applying ANCOVA. Calibration curves prepared in solvent were compared with calibration curves prepared in a blank matrix extract for eight different commodities, establishing whether the matrix induces systematic or proportional errors in the quantification of the pesticides. In such cases correction functions were obtained and validated by quantifying spiked samples using solvent calibrations and applying the correction functions to the data obtained. The results were compared with those obtained by quantification using matrix-matching calibrations and with those from 100% recovery experiments. It was found that the matrix effects can be avoided using the correction functions. Finally the contribution of the correction functions to the uncertainty of the results was estimated as well as their stability during a four month period.     

Photogenotoxicity of mammalian cells: a review of the different assays for in vitro testing

During the past several years, phototoxicity has been studied at the molecular level, and these studies have provided new insights in the field of DNA lesion characterization, DNA repair and cell response to ultraviolet (UV)-induced stress. The development of new antibiotics and antiinflammatory drugs has highlighted the necessity to develop the assessment of phototoxicity in the safety evaluation of new chemical compounds. This paper aims at reviewing the known molecular mechanisms of the cellular response to UV-induced stress, the in vitro methods that can be proposed and used to screen for toxicity of sunlight and the photosensitization process resulting from the activation of drugs by light. UV sources, biological systems and endpoints of interest in that particular objective are listed. Phototoxic effects span from the cytotoxic-apoptotic effect to the induction of primary DNA damage, DNA repair and a variety of stress genes acting on the cell cycle and the fate of the cell. Ultimately, it can lead to the induction of hereditary DNA modification. A variety of assays are proposed to specifically address all these particular consequences of UV-induced toxicity.     

Characterization of multimetallic grid-type complexes by electrospray mass spectrometry

The self-assembly of the terdentate ligands 1a-h, based on terpyridine-like binding sites, with octahedrally coordinated metal ions, such as Fe(II), Co(II), Cu(II), Zn(II), Cd(II), Hg(II) and Pb(II), leads to the formation of the supramolecular grid-type complexes 2a-c(M(II)), 3d-g(M(II)) and 4h(M(II)). The structures and compositions of these coordination complexes in solution were deduced from electrospray mass spectrometry (ESMS) measurements. The results agree with the data available from x-ray radiocrystallography in the solid state and/or NMR spectroscopy in solution. ESMS may be applied in cases where other methods are difficult to use or inconclusive. This study stresses the power of ESMS in supramolecular chemistry.     

Evidence of an equilibrium between selenides and osmium(VIII) reagents and selenoxides and osmium(VI) reagents

Driving the equilibrium between selenides and osmium(VIII) reagents with selenoxides and osmium(VI) by a subsequent reaction (rearrangement of allyl selenoxides to allyl alcohols or addition of osmium(VIII) species on C=C double bonds) to one side, allows the transformation of methyl geranyl selenides to linalool and of methyl citronellyl selenoxide to 6,7-dihydroxy citronellyl selenide.