Laminar optical tomography: demonstration of millimeter-scale depth-resolved imaging in turbid media

Laminar optical tomography (LOT) is a new technique that combines the advantages of diffuse optical tomography image reconstruction and a microscopy-based setup to allow noncontact imaging with 100-200-microm resolution effective over depths of 0-2.5 mm. LOT is being developed primarily for multispectral imaging of rat cortex, for which resolving functional dynamics in various layers of the brain's cortex (to depths of 1500 microm) is of increasing interest to neurophysiologists. System design and image reconstruction techniques are described, along with simulation and phantom results that demonstrate the characteristics and limitations of system accuracy and resolution.     

Acoustic wave sensor for barium based on poly[Ni(salen)(crown)] recognition chemistry

Interfacial recognition of barium by a crown ether receptor is quantified using an acoustic wave sensor, and the isotherm characteristics rationalized in terms of solution complexation chemistry and polymer materials properties.     

New insights into the Belousov-Zhabotinskii reaction derived from EQCM measurements at a gold electrode

Electrochemical quartz crystal microbalance experiments were used to study the classical Belousov-Zhabotinskii (BZ) homogeneous oscillating system. This system involves 2 × 10(-3) M Ce(III), 0.28 M malonic acid and 0.063 M bromate as the main initial components in 1 M sulfuric acid solution. The gold-evaporated electrodes on a 10 MHz AT-cut quartz crystal were used for potentiometric and amperometric studies while the changes in crystal frequency provided mass data. Under open-circuit conditions, during the BZ reaction, oscillations of the gold electrode potential in the range ca. 0.8 to 1.07 V (SCE) with a period about 80 s occurred. They were accompanied by periodic 10-15 ng [i.e. ca. 45-70 ng cm(-2)] changes in the electrode mass. At more positive potentials a decrease in electrode mass occurred, while the mass increased at more negative potentials. At a constant applied electrode potential, corresponding to either the upper or the lower potential limit attained under open-circuit conditions, periodic pulses of cathodic current occurred and were accompanied by mass changes. A continuous decrease in the electrode mass occurred at 1.06 V. A detailed examination of the gold electrode behavior in the solutions containing individual components of the system using cyclic voltammetry and quartz crystal microgravimetry provided the information needed to interpret the mass changes that occur in the complete system. No significant changes in the electrode mass occurred in sulfuric acid solution in the potential range where current and mass oscillations take place in the full BZ reaction solution. The same result was found in sulfuric acid solutions containing either Ce(III) or malonic acid. Dissolution of gold occurred in a sulfuric acid solution containing bromate or bromide ions. Adsorption of bromide ions on gold electrode occurred in Br(-)-containing sulfuric acid solution at more negative potentials. In the BZ system, dissolution of gold in the presence of oxidizing (bromate) and complexing (bromide) species causes the decrease in the electrode mass that accompanies the positive potential jump under open-circuit conditions, or the current pulse that occurs at more negative applied constant potentials. Cathodic current pulses occurring at a constant electrode potential (either 0.8 or 1.06 V) are associated with the reduction of Ce(IV) formed as a result of periodic homogeneous oxidation of Ce(III) by bromate. Bromide ions formed in the course of the BZ reaction appear to play a significant role in electrode mass changes, causing a mass decrease at more positive potentials due to dissolution of gold, and a subsequent mass increase at more negative potentials due to adsorption processes.     

The EQCM: electrogravimetry with a light touch

In its simplest manifestation, the electrochemical quartz crystal microbalance (EQCM) is a relatively new device for executing a classical technique, electrogravimetry. The advantages it brought were in situ applicability (notwithstanding prior misconceptions regarding damping by a contacting fluid), exceptional sensitivity and dynamic capability, thereby permitting real-time monitoring of changes in surface populations of species during electrochemically driven processes. The basis of the method relies on the storage and dissipation of energy injected into the interfacial region by a high frequency (megahertz) acoustic wave; the latter is generated by a piezoelectric (generally quartz) resonator. From modest early aspirations, largely associated with the deposition/dissolution of simple adsorbates and thin metal films, the technique has expanded in three strategic respects: materials, phenomena and methodology. In the first instance, extension to thick electroactive films (notably metal oxides and polymers) has generated considerable insight. Second, the sensitivity of the EQCM to viscoelastic phenomena, stress and interfacial slip has been recognized. Considerable attention has been given to viscoelastic processes in redox and conducting polymers: these have been parameterized in terms of shear moduli, whose variation with polymer structure and imposed conditions provides insight into polymer dynamics. Procedures exist for characterizing film stress in harder materials, but this is less well exploited. Interfacial slip remains a poorly understood area. Third, application in the context of diverse electrochemical control functions and integration with other in situ techniques provide many as yet unexploited opportunities. The extent to which these are realised will probably depend on the level of interpretation of the resultant data, which presently underuses the library of modelling protocols available.     

Aerodynamic and acoustic voice measurements of patients with vocal nodules: variation in baseline and changes across voice therapy.

An important clinical issue concerns the efficacy of current voice therapy approaches in treating voice disorders, such as vocal nodules. Much research focuses on finding reliable methods for documentation of treatment results. In this second treatment study of ten patients with vocal nodules, who participated in a behaviorally based voice therapy program, 11 aerodynamic (transglottal air pressure and glottal waveform) and acoustic (spl, f0, and spectrum slope) measures were used. Three pretherapy baseline assessments were carried out, followed by one assessment after each of five therapy phases. Measurements were made of two types of speech materials: Strings of repeated /pae/ syllables and sustained /ae/ phonations in two loudness conditions: comfortable loudness and loud voice. The data were normalized using z-scores, which were based on data from 22 normal subjects. The results showed that the aerodynamic measures reflected the presence of vocal pathology to a higher degree than did the acoustic spectral measures, and they should be useful in studies comparing nodule and normal voice production. Large individual session-to-session variation was found for all measures across pretherapy baseline recordings, which contributed to nonsignificant differences between baseline and therapy data.     

Polymer modification using difluoromethane (HFC 32) and carbon dioxide

The infusion of difluoromethane (HFC 32) and CO₂ into polystyrene and polyethylene has been characterized using a quartz crystal microbalance technique over a range of temperatures and pressures. The results were adequately modeled by Flory‐Huggins theory. Significant plasticization was observed in the polymeric materials and it is shown that manipulation of the experimental temperature, pressure, and rate of depressurisation can cause significant changes in the morphology of the samples. It is demonstrated for the first time how rate constant data for the kinetics of gas sorption can be extracted quickly and easily from in situ quartz crystal microbalance measurements. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 1072–1083, 2006     

OnL 2-homology and asphericity

We useL ² methods to show that if a group with a presentation of deficiency one is an extension ofZ by a finitely generated normal subgroup then the 2-complex corresponding to any presentation of optimal deficiency is aspherical and to prove a converse of the Cheeger-Gromov-Gottlieb theorem relating Euler characteristic and asphericity. These results are applied to the Whitehead conjecture, 4-manifolds and 2-knot groups.     

Crystal and geometry‐optimized structure of an anthracene‐based Diels–Alder adduct

Computational calculations of an anthracene‐based Diels–Alder adduct, namely, 17‐ethyl‐1‐hydroxymethyl‐17‐azapentacyclo[6.6.5.0^2,7.0^9,14.0^15,19]nonadeca‐2,4,6,9,11,13‐hexaene‐16,18‐dione, C₂₁H₁₉NO₃, predicting density functional theory (DFT) optimized geometries in the gas phase are compared in terms of accuracy relative to the solid‐state crystal structure and computational cost. Crystal structure determination and Hirshfeld surface analysis of the racemic product reveal that the molecules are linked by O—H…O=C hydrogen bonds between the hydroxy and carbonyl groups, accounting for 9.5% of the intermolecular contacts, while H…H contacts represent 56.9% of the total. Boltzmann population analysis of computed relative rotamer abundances in the gas phase are based on lower‐level geometry optimization and thermochemical corrections coupled with higher‐level electronic energy calculations using the B2PLYP double‐hybrid functional. As expected, the choice of density functional has a greater effect than the basis set on accuracy for all levels of theory. For any given functional, increasing the basis set size did not always correlate with increasingly accurate structures. The hybrid functional B3LYP without dispersion correction routinely gave the closest approximations to the crystal structure where the B3LYP/aug‐cc‐pVDZ combination afforded the best structure (r.m.s. deviation = 0.1314 Å). However, the B3LYP/6‐31+G(d,p) level of theory represents the best compromise between accuracy (r.m.s. deviation = 0.1388 Å) and cost as it yielded appreciably accurate results in a fraction of the time compared to other method combinations.     

Free Products and 4-Dimensional Connected Sums

We show that a closed 4-manifold whose fundamental group isa nontrivial free product is stably homeomorphic to one whichadmits a corresponding decomposition into a connected sum, andthat connected sums of copies of S¹ x S³ and S¹ x S³ may becharacterized up to s-cobordism by their fundamental group,Euler characteristic and orientability. These results are appliedto obtain weak splitting and triviality theorems for links inS⁴.