Spectroscopic Study of Acid-base Equilibria and Ion Pairing in Supercritical Methanol

Acid-base equilibria between 2,5-dichlorophenol (DCP) and various bases (LiOH, NaOH, and KOH) were studied in ambient to supercritical methanol, by measuring the absorption spectrum of DCP at alkali metal hydroxide molalities ranging up to 10 mmol⋅kg⁻¹, at temperatures up to 250 °C and a pressure of 25.0 MPa. The spectrum was deconvoluted into contributions for the acidic (HA) and basic (A⁻) forms of DCP, taking into account a blue shift of the phenolate (A⁻) spectrum due to the effect of ion pairing with an alkali metal cation. Degrees of dissociation of DCP determined from the spectra suggested that the dissociation constant of DCP has a maximum around 150 °C, whereas that of KOH decreases with temperature. The phenolate-alkali metal ion pairing was examined from the peak shift of the phenolate spectrum in the presence of Li⁺, Na⁺, and K⁺. A smaller cation radius and higher temperature (thus a lower dielectric constant for methanol) give rise to stronger electrostatic interaction in the ion pair. The basicities of the alkali metal hydroxides in supercritical methanol were compared using DCP as an indicator, and were shown to follow the order LiOH < NaOH ≤ KOH. This order is the same as that for the catalytic effect of alkali metal hydroxides on the methylation of phenol in supercritical methanol (Takebayashi et al.: Ind. Eng. Chem. Res. 47:704–709, 2008). Electronic Supplementary Material  The online version of this article () contains supplementary material, which is available to authorized users.     

The interaction of ultrathin films of Ni and Pd with W(110): an XPS study

The interaction of ultrathin films of Ni and Pd with W(110) has been examined using X-ray photoelectron spectroscopy (XPS) and the effects of annealing temperature and adsorbate coverage (film thickness) are investigated. The XPS data show that the atoms in a monolayer of Pd or Ni supported on W(110) are electronically perturbed with respect to the surface atoms of Pd(100) and Ni(100). The magnitude of the electronic perturbations is larger for Pd than for Ni adatoms. Our results indicate that the difference in Pd(3d_5/2) XPS binding energies between a pseudomorphic monolayer of Pd on W(110) and the surface atoms of Pd(100) correlates with the variations observed for the desorption temperature of CO (i.e., the strength of the Pd---CO bond) on these surfaces. A similar correlation is seen for the Ni(2p_3/2) XPS binding energies of Ni/W(110) and Ni(100) and the CO desorption temperatures from the surfaces. The shifts in XPS binding energies and CO desorption temperatures can be explained in terms of: (1) variations that occur in the Ni---Ni and Pd---Pd interactions when Ni and Pd adopt the lattice parameters of W(110) in a pseudomorphic adlayer; and (2) transfer of electron density from the metal overlayer to the W(110) substrate upon adsorption. Measurements of the Pd(3d_5/2) XP binding energy of Pd/W(110) as a function of film thickness indicate that the Pd---W interaction affects the electronic properties of several layers of Pd atoms.     

Stability and Synchronization of a Ring of Identical Cells with Delayed Coupling

We consider a ring of identical elements with time delayed, nearest neighbour coupling. The individual elements are modelled by a scalar delay differential equation which includes linear decay and nonlinear delayed feedback. The linear stability of the trivial solution is completely analyzed and illustrated in the parameter space of the coupling strength and the coupling delay. Conditions for global stability of the trivial solution are also given. The bifurcation and stability of nontrivial synchronous solutions from the trivial solution is analyzed using a centre manifold construction.Dedicated to Professor Shui-Nee Chow on the occasion of his 60th birthday.     

Further assessment of forward pressure level for in situ calibration

Quantifying ear-canal sound level in forward pressure has been suggested as a more accurate and practical alternative to sound pressure level (SPL) calibrations used in clinical settings. The mathematical isolation of forward (and reverse) pressure requires defining the The?venin-equivalent impedance and pressure of the sound source and characteristic impedance of the load; however, the extent to which inaccuracies in characterizing the source and/or load impact forward pressure level (FPL) calibrations has not been specifically evaluated. This study examined how commercially available probe tips and estimates of characteristic impedance impact the calculation of forward and reverse pressure in a number of test cavities with dimensions chosen to reflect human ear-canal dimensions. Results demonstrate that FPL calibration, which has already been shown to be more accurate than in situ SPL calibration, can be improved particularly around standing-wave null frequencies by refining estimates of characteristic impedance. Better estimates allow FPL to be accurately calculated at least through 10 kHz using a variety of probe tips in test cavities of different sizes, suggesting that FPL calibration can be performed in ear canals of all sizes. Additionally, FPL calibration appears a reasonable option when quantifying the levels of extended high-frequency (10-18 kHz) stimuli.     

Active to sterile neutrino mixing limits from neutral-current interactions in MINOS

Results are reported from a search for active to sterile neutrino oscillations in the MINOS long-baseline experiment, based on the observation of neutral-current neutrino interactions, from an exposure to the NuMI neutrino beam of 7.07×10(20) protons on target. A total of 802 neutral-current event candidates is observed in the Far Detector, compared to an expected number of 754 ± 28(stat) ± 37(syst) for oscillations among three active flavors. The fraction f(s) of disappearing ν(μ) that may transition to ν(s) is found to be less than 22% at the 90% C.L.     

Measurement of the neutrino mass splitting and flavor mixing by MINOS

Measurements of neutrino oscillations using the disappearance of muon neutrinos from the Fermilab NuMI neutrino beam as observed by the two MINOS detectors are reported. New analysis methods have been applied to an enlarged data sample from an exposure of 7.25×10(20) protons on target. A fit to neutrino oscillations yields values of |Δm(2)|=(2.32(-0.08)(+0.12))×10(-3) eV(2) for the atmospheric mass splitting and sin(2)(2θ)>0.90 (90% C.L.) for the mixing angle. Pure neutrino decay and quantum decoherence hypotheses are excluded at 7 and 9 standard deviations, respectively.     

The 2-D growth of gold on single-layer graphene/Ru(0001): Enhancement of CO adsorption

The growth and morphology of two-dimensional (2-D) gold islands on a single-layer graphene supported on Ru(0001) have been studied by scanning tunneling microscopy (STM). Our findings show that gold exhibits 2-D structures up to a gold dosage of 0.75 equivalent monolayers, and that these 2-D gold islands are thermally stable at room temperature. Parallel polarization modulation infrared reflection absorption spectroscopic (PM-IRAS) and high resolution electron energy loss spectroscopic (HREELS) studies indicate that carbon monoxide (CO) adsorbs on these 2-D gold islands at 85 K, showing a characteristic CO stretching feature at 2095 cm^? 1 for a saturation coverage of CO. The red shift of the CO stretching frequency compared to that on charge neutral gold is consistent with electron transfer from graphene to gold, i.e., an electron-rich gold overlayer. Preliminary data obtained by dosing molecular oxygen onto this CO pre-covered surface suggest that the 2-D gold islands catalyze the oxidation of CO.     

The hydrological response of heavy clay grassland soils to rainfall in south‐west England using δ2H

Stable isotopes of water have been previously used in catchment studies to separate rain‐event water from pre‐event groundwater. However, there are a lack of studies at the smaller scale looking at the separation of event water from pre‐event water. This is particularly relevant for heavy clay soil systems through which the movement of water is uncertain but is thought to be rainwater‐dominated. The data presented here were collected at a rural site in the south‐west of England. The historic rainfall at the site was isotopically varied but similar to the global meteoric water line, with annual weighted means of ?37‰ for δ²H and ?5.7‰ for δ¹⁸O and with no seasonal variation. Drainage was sampled from the inter‐flow (surface runoff + lateral through‐flow) and drain‐flow (55 cm deep mole drains) pathways of two 1 ha lysimeters during two rainfall events, which had δ²H values of ?68‰ and ?92‰, respectively. The δ²H values of the lysimeter drainage water suggest that there was no contribution of event water during the first, small discharge (Q) event; however, the second larger event did show isotopic variation in δ²H values negatively related to Q indicating that rainwater was contributing to Q. A hydrograph separation indicated that only 49–58% of the inter‐flow and 18–25% of the drain‐flow consisted of event water. This was surprising given that these soil types are considered retentive of soil water. More work is needed on heavy clay soils to understand better the nature of water movement from these systems. Copyright © 2010 John Wiley & Sons, Ltd.