Measurements of the generalized electric and magnetic polarizabilities of the proton at low Q2 using the virtual-compton-scattering reaction

The mean square polarizability radii of the proton have been measured for the first time in a virtual-Compton-scattering experiment performed at the MIT-Bates out-of-plane scattering facility. Response functions and polarizabilities obtained from a dispersion analysis of the data at Q2 = 0.057 GeV2/c2 are in agreement with O(p3) heavy baryon chiral perturbation theory. The data support the dominance of mesonic effects in the polarizabilities.     

Initial value problem solution of nonlinear shallow water-wave equations

The initial value problem solution of the nonlinear shallow water-wave equations is developed under initial waveforms with and without velocity. We present a solution method based on a hodograph-type transformation to reduce the nonlinear shallow water-wave equations into a second-order linear partial differential equation and we solve its initial value problem. The proposed solution method overcomes earlier limitation of small waveheights when the initial velocity is nonzero, and the definition of the initial conditions in the physical and transform spaces is consistent. Our solution not only allows for evaluation of differences in predictions when specifying an exact initial velocity based on nonlinear theory and its linear approximation, which has been controversial in geophysical practice, but also helps clarify the differences in runup observed during the 2004 and 2005 Sumatran tsunamigenic earthquakes.     

The Bradley–Terry condition is L1-testable

We provide an algorithm with constant running time that given a weighted tournament $T$, distinguishes with high probability of success between the cases that $T$ can be represented by a Bradley–Terry model, or cannot even be approximated by one. The same algorithm tests whether the corresponding Markov chain is reversible.     

An Eberhard-Like Theorem for Pentagons and Heptagons

Eberhard proved that for every sequence (p _k ), 3≤k≤r, k≠6, of nonnegative integers satisfying Euler’s formula ∑ _k≥3(6−k)p _k =12, there are infinitely many values p ₆ such that there exists a simple convex polyhedron having precisely p _k faces of size k for every k≥3, where p _k =0 if k>r. In this paper we prove a similar statement when nonnegative integers p _k are given for 3≤k≤r, except for k=5 and k=7 (but including p ₆). We prove that there are infinitely many values p ₅,p ₇ such that there exists a simple convex polyhedron having precisely p _k faces of size k for every k≥3. We derive an extension to arbitrary closed surfaces, yielding maps of arbitrarily high face-width. Our proof suggests a general method for obtaining results of this kind.     

Direct injection liquid chromatography/electrospray ionization mass spectrometric horse urine analysis for the quantification and confirmation of threshold substances for doping control. II. Determination of theobromine

In equine sport, theobromine is prohibited with a threshold level of 2 µg mL^?1 in urine, hence doping control laboratories have to establish quantitative and qualitative methods for its determination. Two simple liquid chromatography/mass spectrometry (LC/MS) methods for the identification and quantification of theobromine were developed and validated using the same sample preparation procedure but different mass spectrometric systems: ion trap mass spectrometry (ITMS) and time‐of‐flight mass spectrometry (TOFMS). Particle‐free diluted urine samples were directly injected into the LC/MS systems, avoiding the time‐consuming extraction step. 3‐Propylxanthine was used as the internal standard. The tested linear range was 0.75–15 µg mL^?1. Matrix effects were evaluated analyzing calibration curves in water and different fortified horse urine samples. A great variation in the signal of theobromine and the internal standard was observed in different matrices. To overcome matrix effects, a standard additions calibration method was applied. The relative standard deviations of intra‐ and inter‐day analysis were lower than 8.6 and 7.2%, respectively, for the LC/ITMS method and lower than 5.7 and 5.8%, respectively, for the LC/TOFMS method. The bias was less than 8.7% for both methods. The methods were applied to two case samples, demonstrating simplicity, accuracy and selectivity. Copyright © 2009 John Wiley & Sons, Ltd.     

XAS characterization of end-on and side-on peroxoiron(III) complexes of the neutral pentadentate N-donor ligand N-methyl-N,N',N'-tris(2-pyridylmethyl)ethane-1,2-diamine

Peroxo intermediates are implicated in the catalytic cycles of iron enzymes involved in dioxygen metabolism. X-ray absorption spectroscopy has been used to gain insight into the iron coordination environments of the low-spin complex [Fe(III)(Me-TPEN)(eta(1)-OOH)](2+)(1) and the high-spin complex [Fe(III)(Me-TPEN)(eta(2)-O(2))](+)(2)(the neutral pentadentate N-donor ligand Me-TPEN =N-methyl-N,N',N'-tris(2-pyridylmethyl)ethane-1,2-diamine) and obtain metrical parameters unavailable from X-ray crystallography. The complexes exhibit relatively large pre-edge peak areas of approximately 15 units, indicative of iron centers with significant distortions from centrosymmetry. These distortions result from the binding of peroxide, either end-on hydroperoxo for 1 (r(Fe-O)= 1.81A) or side-on peroxo for 2 (r(Fe-O)= 1.99 A). The XAS analyses of 1 strongly support a six-coordinate low-spin iron(III) center coordinated to five nitrogen atoms from Me-TPEN and one oxygen atom from an end-on hydroperoxide ligand. However, the XAS analyses of 2 are not conclusive: Me-TPEN can act either as a pentadentate ligand to form a seven-coordinate peroxo complex, which has precedence in the DFT geometry optimization of [Fe(III)(N4Py)(eta(2)-O(2))](+)(the neutral pentadentate N-donor ligand N4Py =N,N-bis(2-pyridylmethyl)-N-bis(2-pyridyl)methylamine), or as a tetradentate ligand with a dangling pyridylmethyl arm to form a six-coordinate peroxo complex, which is precedented by the crystal structure of [Fe(2)(III)(Me-TPEN)(2)(Cl)(2)(mu-O)](2+).     

Density functional study of neutral allopurinol tautomeric forms

Optimized structures and total molecular energy density functional theory calculations for the 14 possible neutral allopurinol tautomers give the decreasing stability order for the three most stable forms. Several molecular and electronic structure properties, the stabilities in oxidation and reduction processes, the tautomeric equilibrium constants, and the IR vibrational spectra were obtained for these. Those properties corresponding to the ketonic forms are discussed and compared with the theoretical ones for the two most stable species of the isomer hypoxanthine. A noticeable agreement is found between the predicted properties and the experimental behavior known up to date for both isomers. ©1999 John Wiley & Sons, Inc. J Comput Chem 20: 200–206, 1999     

Synthesis and characterization of amphiphilic diblock copolymers of methyl tri(ethylene glycol) vinyl ether and isobutyl vinyl ether

Water-soluble diblock copolymers of methyl tri(ethylene glycol) vinyl ether (hydrophilic block) and isobutyl vinyl ether (hydrophobic block) of different molecular weights and composition were synthesized by living cationic polymerization. The molecular weight and comonomer composition of these copolymers were determined by GPC and ¹H NMR spectroscopy, respectively. Aqueous solutions of the copolymers were characterized in terms of their micellar behavior using dynamic light scattering, aqueous GPC, and dye solubilization. All the copolymers formed aggregates with the exception of a diblock copolymer with only two hydrophobic monomer units. The micellar hydrodynamic size scaled with the 0.61 power of the number of hydrophobic units, in good agreement with a theoretical exponent of 0.73. An increase in the length of the hydrophobic block at constant hydrophilic block length or an increase in the overall polymer size at constant block length ratio both resulted in lower critical micelle concentrations (cmcs). The cloud points of 1% w/w aqueous solutions of the polymers were determined by turbidimetry. An increase in the length of the hydrophobic block at constant hydrophilic block length caused a decrease in the cloud points of the copolymers. However, an increase in the overall polymer size at constant block length ratio led to an increase in the cloud point. © 1996 John Wiley & Sons, Inc.