Effects of masker-spectral variability and masker fringes in children and adults

This study examined the degree to which masker-spectral variability contributes to children's susceptibility to informational masking. Listeners were younger children (5-7 years), older children (8-10 years), and adults (19-34 years). Masked thresholds were measured using a 2IFC, adaptive procedure for a 300-ms, 1000-Hz signal presented simultaneously with (1) broadband noise, (2) a random-frequency ten-tone complex, or (3) a fixed-frequency ten-tone complex. Maskers were presented at an overall level of 60 dB SPL. Thresholds were similar across age for the noise condition. Thresholds for most children were higher than for most adults, however, for both ten-tone conditions. The average difference in threshold between random and fixed ten-tone conditions was comparable across age, suggesting a similar effect of reducing masker-spectral variability in children and adults. Children appear more likely to be susceptible to informational masking than adults, however, both with and in the absence of masker-spectral variability. The addition of a masker fringe (delayed onset of signal relative to masker) provided a release from masking for fixed and random ten-tone conditions in all age groups, suggesting at least part of the masking observed for both ten-tone maskers was informational.     

Python implementation of the restrained electrostatic potential charge model

The restrained electrostatic potential (RESP) charge model is widely used in molecular dynamics simulations, especially for the AMBER and GAFF force fields. We have implemented the RESP scheme using the accessible and widely used Python language and the NumPy numerical library. This article provides a programming-oriented introduction to the RESP scheme and highlights some of the features of NumPy that are useful in scientific computing.     

On the relationship between the apparent diffusion coefficient and extravascular extracellular volume fraction in human breast cancer

MRI techniques have been developed that can noninvasively probe the apparent diffusion coefficient (ADC) of water via diffusion-weighted MRI (DW-MRI). These methods have found much application in cancer where it is often found that the ADC within tumors is inversely correlated with tumor cell density, so that an increase in ADC in response to therapy can be interpreted as an imaging biomarker of positive treatment response. Dynamic contrast enhanced MRI (DCE-MRI) methods have also been developed and can noninvasively report on the extravascular extracellular volume fraction of tissues (denoted by v_e). By conventional reasoning, the ADC should therefore also be directly proportional to v_e. Here we report measurements of both ADC and v_e obtained from breast cancer patients at both 1.5 and 3.0 T. The 1.5-T data were acquired as part of normal standard of care, while the 3.0-T data were obtained from a dedicated research protocol. We found no statistically significant correlation between ADC and v_e for the 1.5- or 3.0-T patient sets on either a voxel-by-voxel or a region-of-interest (ROI) basis. These data, combined with similar results from other disease sites in the literature, may indicate that the conventional interpretation of either ADC, v_e or their relationship is not sufficient to explain experimental findings.     

Inorganic chemistry and IONiC: an online community bringing cutting-edge research into the classroom

This Viewpoint highlights creative ways that members of the Interactive Online Network of Inorganic Chemists (IONiC) are using journal articles from Inorganic Chemistry to engage undergraduate students in the classroom. We provide information about specific educational materials and networking features available free of charge to the inorganic community on IONiC's web home, the Virtual Inorganic Pedagogical Electronic Resource (VIPEr, www.ionicviper.org ) and describe the benefits of joining this community.     

Asymmetric hydrogenation of alkenes with planar chiral 2-phosphino-1-aminoferrocene-iridium(I) complexes

The first highly enantioenriched and enantiopure planar chiral 2-phosphino-1-aminoferrocene ligands and their Ir(COD)BAr_F complexes are reported. The ligands display bidentate coordination behavior towards iridium, as indicated by trends in ³¹P and ¹H NMR spectra of the phosphine moieties and the α to nitrogen substituents of the amines. All of the new complexes showed good reactivity as catalysts in promoting asymmetric hydrogenation of several prochiral alkenes, with enantioselectivities up to 92%. Iridium complexes of dimethylaminoferrocene derivatives containing P-Ar groups [PPh₂ and P(o-tol)₂] gave the highest levels of asymmetric induction.     

Polarons, bipolarons, and side-by-side polarons in reduction of oligofluorenes

The nature of charge carriers in conjugated polymers was elucidated through optical spectroscopy following single- and multielectron reduction of 2,7-(9,9-dihexylfluorene) oligomers, F(n), n = 1-10, yielding spectra with the two bands typical of polarons upon single reduction. For short oligomers addition of a second electron gave a single band demonstrating the classic polaron-bipolaron transition. However, for long oligomers double reductions yielded spectra with two bands, better described as two polarons, possibly residing side-by-side in the F(n) chains. The singly reduced anions do not appear to delocalize over the entire length of the longer conjugated systems; instead they are polarons occupying approximately four fluorene repeat units. The polarons of F(3) and F(4) display sharp absorption bands, but for longer oligomers the bands broaden, possibly due to fluctuations of the lengths of these unconfined polarons. DFT calculations with long-range-corrected functionals were fully consistent with the experiments describing polarons in anions, bipolarons in dianions of short oligomers, and side-by-side polarons in dianions of long oligomers, while results from standard functionals were not compatible with the experimental results. The computations found F(10)(2-), for example, to be an open-shell singlet ( ≈ 1), with electrons in two side-by-side orbitals, while dianions of shorter oligomers experienced a gradual transition to bipolarons with states of intermediate character at intermediate lengths. The energies and extinction coefficients of each anionic species were measured by ultraviolet-visible-near-infrared absorption spectroscopy with chemical reduction and pulse radiolysis. Reduction potentials determined from equilibria mirrored oxidation potentials reported by Chi and Wegner. Anions of oligomers four or more units in length contained vestigial neutral (VN) absorption bands that arise from neutral parts of the chain. Energies of the VN bands correspond to those of oligomers shorter by four units.     

Simultaneous PET–MRI in oncology: a solution looking for a problem?

With the recent development of integrated positron emission tomography–magnetic resonance imaging (PET–MRI) scanners, new possibilities for quantitative molecular imaging of cancer are realized. However, the practical advantages and potential clinical benefits of the ability to record PET and MRI data simultaneously must be balanced against the substantial costs and other requirements of such devices. In this review, we highlight several of the key areas where integrated PET–MRI measurements, obtained simultaneously, are anticipated to have a significant impact on clinical and/or research studies. These areas include the use of MR-based motion corrections and/or a priori anatomical information for improved reconstruction of PET data, improved arterial input function characterization for PET kinetic modeling, the use of dual-modality contrast agents, and patient comfort and practical convenience. For widespread acceptance, a compelling case could be made if the combination of quantitative MRI and specific PET biomarkers significantly improves our ability to assess tumor status and response to therapy, and some likely candidates are now emerging. We consider the relative advantages and disadvantages afforded by PET–MRI and summarize current opinions and evidence as to the likely value of PET–MRI in the management of cancer.     

Synthesis of novel furo-pyran derivatives via reaction between an isocyanide and alkylidene-substituted Meldrum’s acid

An unexpected four-component (3+1) reaction of an alkyl isocyanide with alkylidene-substituted Meldrum’s acid in CH₂Cl₂ at room temperature produces imino-furopyranones in good yields. The structures of the products are deduced from their IR, ¹H NMR, and ¹³C NMR spectra and by X-ray analysis. The products are structurally similar to 2H-furo[2,3-c]pyran-2-one natural products.     

A Fast Algorithm for Two-Dimensional Elliptic Problems

In this paper, we extend the work of Daripa et al. [14–16,7] to a larger class of elliptic problems in a variety of domains. In particular, analysis-based fast algorithms to solve inhomogeneous elliptic equations of three different types in three different two-dimensional domains are derived. Dirichlet, Neumann and mixed boundary value problems are treated in all these cases. Three different domains considered are: (i) interior of a circle, (ii) exterior of a circle, and (iii) circular annulus. Three different types of elliptic problems considered are: (i) Poisson equation, (ii) Helmholtz equation (oscillatory case), and (iii) Helmholtz equation (monotone case). These algorithms are derived from an exact formula for the solution of a large class of elliptic equations (where the coefficients of the equation do not depend on the polar angle when written in polar coordinates) based on Fourier series expansion and a one-dimensional ordinary differential equation. The performance of these algorithms is illustrated for several of these problems. Numerical results are presented.