Sparse 1D discrete Dirac operators I: Quantum transport

Some dynamical lower bounds for one-dimensional discrete Dirac operators with different classes of sparse potentials are presented, and the particular role of the particle mass is emphasized.     

Stereoselective synthesis of o-bromo (or iodo)aryl P-chirogenic phosphines based on aryne chemistry

The efficient synthesis of chiral or achiral tertiary phosphines bearing an o-bromo (or iodo)aryl substituent is described. The key step of this synthesis is based on the reaction of a secondary phosphine borane with the 1,2-dibromo (or diiodo)arene, owing to the formation in situ of an aryne species in the presence of n-butyllithium. When P-chirogenic secondary phosphine boranes were used, the corresponding o-halogeno-arylphosphine boranes were obtained without racemization in moderate to good yields and with ee up to 99%. The stereochemistry of the reaction, with complete retention of the configuration at the P atom, has been established by X-ray structures of P-chirogenic o-halogenophenyl phosphine borane complexes. The decomplexation of the borane was easily achieved without racemization using DABCO to obtain the free o-halogeno-arylphosphines in high yields.     

NMR hand-held moisture sensor.

An open magnet design, hand-held NMR sensor head is presented. Wood moisture content and cement hydration tests demonstrate the potential of the tool for in-situ material assessment. The magnetic field distribution was adjusted by positioning blocks of permanent magnets using millimeter scale 3-dimensional magnetic field modeling. A low Q-factor circuit was used for spin-echo sequences with short echo times.     

Adsorption and preconcentration of 2,4-dichlorophenoxyacetic acid on a chemically modified silica gel surface

The herbicide 2,4-dichlorophenoxyacetic acid (2,4-D), chemically anchored to a silica gel surface, was used to adsorb and preconcentrate the same herbicide from aqueous solutions at room temperature. From a series of adsorption isotherms adjusted to a modified Langmuir equation, the maximum number of moles adsorbed was calculated as 4.67 x 10(-5) mol g(-1), with the highest retention capacity at pH 5. This modified silica gel was used in a column for preconcentrating trace levels of 2,4-D. The preconcentrated herbicide can be directly eluted with methanol with a recovery efficiency higher than 97%. The concentration factor was 8.33.     

catena‐Poly­[fac‐tri­chloro­methyl­tin(IV)‐μ‐[meso‐1,2‐bis­(phenyl­sulfinyl)­ethane‐O:O′]]

In the title compound, [SnCl₃(CH₃)(C₆H₅SOCH₂)₂]_n, the octahedral Sn^IV centres are bridged by meso‐1,2‐bis­(phenyl­sulfinyl)­ethane ligands forming infinite chains along the [100] direction.     

Biseugenol Exhibited Anti-Inflammatory and Anti-Asthmatic Effects in an Asthma Mouse Model of Mixed-Granulocytic Asthma

In the present work, the anti-inflammatory and antiasthmatic potential of biseugenol, isolated as the main component from n-hexane extract from leaves of Nectandra leucantha and chemically prepared using oxidative coupling from eugenol, was evaluated in an experimental model of mixed-granulocytic asthma. Initially, in silico studies of biseugenol showed good predictions for drug-likeness, with adherence to Lipinski’s rules of five (RO5), good Absorption, Distribution, Metabolism and Excretion (ADME) properties and no alerts for Pan-Assay Interference Compounds (PAINS), indicating adequate adherence to perform in vivo assays. Biseugenol (20 mg·kg⁻¹) was thus administered intraperitoneally (four days of treatment) and resulted in a significant reduction in both eosinophils and neutrophils of bronchoalveolar lavage fluid in ovalbumin-sensitized mice with no statistical difference from dexamethasone (5 mg·kg⁻¹). As for lung function parameters, biseugenol (20 mg·kg⁻¹) significantly reduced airway and tissue damping in comparison to ovalbumin group, with similar efficacy to positive control dexamethasone. Airway hyperresponsiveness to intravenous methacholine was reduced with biseugenol but was inferior to dexamethasone in higher doses. In conclusion, biseugenol displayed antiasthmatic effects, as observed through the reduction of inflammation and airway hyperresponsiveness, with similar effects to dexamethasone, on mixed-granulocytic ovalbumin-sensitized mice.     

The Mystery of the Benzene-Oxide/Oxepin Equilibrium—Heavy-Atom Tunneling Reversed by Solvent Interactions

The equilibrium between benzene oxide ( 1 ) and oxepin ( 2 ) is of large importance for understanding the degradation of benzene in biological systems and in the troposphere. Our studies reveal that at cryogenic temperatures, this equilibration is governed by rare heavy-atom tunneling. In solid argon at 3 K, 1 rearranges to 2 via tunneling with a rate constant of approximately 5.3×10⁻⁵ s⁻¹. Thus, in a nonpolar environment, 2 is slightly more stable than 1 , in agreement with calculations at the CCSD(T) level of theory. However, if the argon is doped with 1 % of H₂O or CF₃I as typical hydrogen or halogen bond donors, respectively, weak complexes of 1 and 2 are formed, and now 2 is tunneling back to form 1 . Thus, by forming non-covalent complexes, 1 becomes slightly more stable than 2 and the direction of the heavy-atom tunneling is reversed.     

Non-Markovian Diffusion Over a Saddle with a Generalized Langevin Equation

The diffusion over a simple parabolic barrier is exactly solved with a non-Markovian Generalized Langevin Equation. For a short relaxation time, the problem is shown to be similar to a Markovian one, with a smaller effective friction. But for longer relaxation time, the average trajectory starts to oscillate and the system can have a very fast first passage over the barrier. For very long relaxation times, the solution tends to a zero-friction limit. PACS: 02.50.EY, 05.40.−a, 25.70.Jj     

Threat localization in QR explosive detection systems

The detection of explosives for the purpose of aviation security is an important task for preventing terrorism acts and smuggling. A number of methods for explosive screening have been developed. For the purpose of aviation security, the inspections are performed on passengers, their carry-on luggage, checked baggage, and cargo containers. An effective explosive detection system should be capable of reporting the type of energetic material, the mass, the object shape and its location within the volume being scanned. Quadrupole resonance (QR) is a mature technique for detecting and classifying explosives concealed in unopened containers. We report recent research on threat localization techniques, aimed to enhance the efficiency of QR-based baggage scanner systems. The methods investigated for threat localization are based on the effect of inhomogeneous static magnetic fields, nonuniform radio-frequency excitation, and the use of spatially selective radio-frequency coils for one- and two-dimensional mapping.     

Anomalous small‐angle X‐ray scattering characterization of composites based on sulfonated poly(ether ether ketone), zirconium phosphates,and zirconium oxide

The morphology and distribution of zirconium oxide and zirconium phosphates in a matrix of sulfonated poly(ether ether ketone) (SPEEK) were investigated with anomalous small‐angle X‐ray scattering (ASAXS) and electron microscopy. ASAXS revealed that ZrO₂ was distributed in the SPEEK matrix in the form of nanoparticles smaller than 13 Å. A decrease in the conductivity suggested that the sulfonic groups were bound to the zirconium oxo species at the particle surface. Furthermore, two kinds of membranes containing zirconium phosphate were investigated. In one case, the phosphate was directly dispersed in the polymer solution for the casting of the membrane. In the other case, the phosphate was previously treated with n‐propyl ammonium and polybenzimidazole. From ASAXS data, the fractal dimension could be estimated. Mass‐fractal behavior was confirmed for the SPEEK membrane containing previously exfoliated zirconium phosphate, with aggregates of 6.3–165 Å. Surface‐fractal behavior was detected for membranes with untreated phosphates, with aggregates of 6.4–185 Å. The untreated phosphates caused an increase in the permeability, without changing the proton conductivity much. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 567–575, 2004