A measure of curve fitting error for noise filtering diffusion tensor MRI data

A parameter, chi2p, based on the fitting error was introduced as a measure of reliability of DT-MRI data, and its properties were investigated in simulations and human brain data. Its comparison with the classic chi2 revealed its sensitivity to both the goodness of fit and the pixel signal-to-noise-ratio (SNR), unlike the classic chi2, which is sensitive only to the goodness of fit. The new parameter was thus able to separate effectively pixels with coherent signals (having small fitting error and/or high SNR) from those with random signals (having inconsistent fitting and/or low SNR). A practical advantage of chi2p over the classic chi2 was that chi2p is quantified directly from the data of each pixel, without requiring accurate estimation of data-dependent parameters (such as noise variance), which often makes application of the classic chi2 problematic. Analytical approximations of chi2p enabled an objective (data-independent) and automated calculation of a threshold value, used for internal scaling of the chi2p map. Apart from assessing data reliability on a pixel-by-pixel basis, chi2p was used to develop an objective and generic methodology for the exclusion of pixels with unreliable DT information by discarding pixels with chi2p values exceeding the threshold. Pixels corresponding to very low SNR, and poorly fitted cerebrospinal fluid and surrounding brain tissue, had increased chi2p values and were successfully excluded, providing DT anisotropy maps free from artifactual anisotropic appearance.     

Influence of the glass transition on solvent loss from spin-cast glassy polymer thin films

The interdependence of solvent loss and vitrification in spin-cast poly(methyl methacrylate) thin films is explored. Fast measurements of decreases in film thickness, achieved with ellipsometry, indicate that the rate of solvent (toluene) loss decreases sharply when the solvent volume fraction phi(solv) falls below about 0.15 and the film vitrifies. Ellipsometry and microgravimetry show that solvent is lost from a glassy thin film (150 nm thick) over of a period of more than ten hours, which is much longer than would be required if it was limited by diffusion in the glass. These results support the recently-proposed idea that the compression of the glass creates an energy barrier that slows down solvent loss.     

Metabonomic analysis of mouse urine by liquid-chromatography-time of flight mass spectrometry (LC-TOFMS): detection of strain,diurnal and gender differences

The application of HPLC-MS combined with principal components analysis (PCA) to the metabonomic analysis of mouse urine is demonstrated. Urine samples from three strains of mouse were analysed by gradient HPLC-MS combined with positive and negative electrospray time-of-flight mass spectrometry. Analysis of the resulting data using PCA enabled the samples to be discriminated between on the basis of gender, strain and diurnal variation. These preliminary results suggest that HPLC-MS-based approaches may have a useful role in metabonomic analysis that complements existing approaches.     

Unnatural selection: talent identification and development in sport

The early identification of talented individuals has become increasingly important across many performance domains. Current talent identification (TI) schemes in sport typically select on the basis of discrete, unidimensional measures at unstable periods in the athlete's development. In this article, the concept of talent is revised as a complex, dynamical system in which future behaviors emerge from an interaction of key performance determinants such as psychological behaviors, motor abilities, and physical characteristics. Key nonlinear dynamics concepts are related to TI approaches such as sensitivity to initial conditions, transitions, and exponential behavioral distributions. It is concluded that many TI models place an overemphasis on early identification rather than the development of potentially talented performers. A generic model of talent identification and development is proposed that addresses these issues and provides direction for future research.     

Computing isogeny covariant differential modular forms

We present the computation modulo and explicit formulas for the unique isogeny covariant differential modular form of order one and weight called , an isogeny covariant differential modular form of order two and weight denoted by , and an isogeny covariant differential modular form of order two and weight .

     

Optical parametric oscillator with a pulse repetition rate of 39 GHz and 2.1-W signal average output power in the spectral region near 1.5 microm

We present a singly resonant, synchronously pumped optical parametric oscillator with a record-high repetition rate of 39 GHz. The transform-limited 2.2-ps pulses at 1570 nm have as much as 2.1-W average output power. The all-solid-state pump source is based on a diode-pumped passively mode-locked 39-GHz Nd:YVO4 laser and an efficient ytterbium-doped fiber amplifier.     

Double-pass axially resolved confocal Mueller matrix imaging polarimetry

We present experimental depth-resolved complete polarization-sensitive measurements of a stack of linear retarders and glass plates by using what is to the best of our knowledge the first combination of a confocal imaging system with a complete Mueller matrix polarimeter. The axially resolved Mueller matrices were compared with a forward simulation, with good agreement.     

Synthesis and cytotoxicity of novel sansalvamide A derivatives

Described are the syntheses of 14 derivatives of the natural product Sansalvamide A, where two are more active against HCT 116 colon cancer cell lines than the natural product. These derivatives were synthesized using a combinatorial-type strategy that permits elucidation of the amino acid role in the cytotoxicity, and they lay the groundwork for development of new anticancer agents. [structure: see text]