Controlling the false positive rate in fuzzy clustering using randomization: application to fMRI activation detection

Despite its potential advantages for fMRI analysis, fuzzy C-means (FCM) clustering suffers from limitations such as the need for a priori knowledge of the number of clusters, and unknown statistical significance and instability of the results. We propose a randomization-based method to control the false-positive rate and estimate statistical significance of the FCM results. Using this novel approach, we develop an fMRI activation detection method. The ability of the method in controlling the false-positive rate is shown by analysis of false positives in activation maps of resting-state fMRI data. Controlling the false-positive rate in FCM allows comparison of different fuzzy clustering methods, using different feature spaces, to other fMRI detection methods. In this article, using simulation and real fMRI data, we compare a novel feature space that takes the variability of the hemodynamic response function into account (HRF-based feature space) to the conventional cross-correlation analysis and FCM using the cross-correlation feature space. In both cases, the HRF-based feature space provides a greater sensitivity compared to the cross-correlation feature space and conventional cross-correlation analysis. Application of the proposed method to finger-tapping fMRI data, using HRF-based feature space, detected activation in sub-cortical regions, whereas both of the FCM with cross-correlation feature space and the conventional cross-correlation method failed to detect them.     

Synthesis of the fully functionalized ABCDE ring moiety of ciguatoxin

A fully functionalized ABCDE ring moiety of ciguatoxin (CTX), the major causative agent of ciguatera poisoning, was synthesized for the first time. The present strategy involves the efficient installation of the C5-dihydroxybutenyl substituent and construction of the tetrahydrooxepin E ring using a novel alpha-chlorosulfide synthon. [structure: see text]     

Total synthesis of (+)-tanikolide via oxidative lactonization

(+)-Tanikolide has been synthesized in eight linear steps with a 31% overall yield. The key step in the synthesis utilizes a recently developed tandem oxidative cleavage-lactonization of a precursor alkenol to deliver the lactone moiety.     

Upper limits on a stochastic background of gravitational waves

The Laser Interferometer Gravitational-Wave Observatory has performed a third science run with much improved sensitivities of all three interferometers. We present an analysis of approximately 200 hours of data acquired during this run, used to search for a stochastic background of gravitational radiation. We place upper bounds on the energy density stored as gravitational radiation for three different spectral power laws. For the flat spectrum, our limit of omega0 < 8.4 x 10(-4) in the 69-156 Hz band is approximately 10(5) times lower than the previous result in this frequency range.     

Transformations in the medium-range order of fused silica under high pressure

Molecular dynamics simulations of fused silica at shock pressures reproduce the experimental equation of state of this material and explain its characteristic shape. We demonstrate that shock waves modify the medium-range order of this amorphous system, producing changes that are only clearly revealed by its ring size distribution. The ring size distribution remains practically unchanged during elastic compression but varies continuously after the transition to the plastic regime.     

Lithium trifluoromethanesulfonate (LiOTf) as a recyclable catalyst for highly efficient acetylation of alcohols and diacetylation of aldehydes under mild and neutral reaction conditions

A variety of alcohols and aldehydes were reacted with acetic anhydride at room temperature in the presence of a catalytic amount of lithium triflate (LiOTf) to produce the corresponding esters and 1,1-diacetates, respectively, in good to excellent yields under essentially neutral reaction conditions. Sensitive functional groups such as PhCO(2)-, OMe, and OTBDMS ethers survived intact under the described reaction conditions.     

Facile oxidation of aldehydes to acids and esters with Oxone

[reaction: see text] A highly efficient, mild, and simple protocol is presented for the oxidation of aldehydes to carboxylic acids utilizing Oxone as the sole oxidant. Direct conversion of aldehydes in alcoholic solvents to their corresponding ester products is also reported. These reactions may prove to be valuable alternatives to traditional metal-mediated oxidations.     

Improving the Photocatalytic Activity of Modified Anatase TiO2 with Different Concentrations of Aluminum under Visible Light: Mechanistic Survey

Visible light‐driven Al‐doped TiO₂ with different aluminum contents (2, 5 and 10 mol%) were synthesized via a facile sol–gel method. Fourier transform infrared (FTIR), UV‐visible diffuse reflectance, energy dispersive X‐ray (EDX) spectroscopy as well as X‐ray diffraction (XRD), X‐ray fluorescence (XRF) and scanning electron microscopy (SEM) methods were used for the characterization of the obtained nanoparticles. The photocatalytic performance of the samples was evaluated by the degradation of rhodamine B (RhB) under visible light irradiation. The yield of the degradation RhB was estimated to be 71%, 89%, 65% and 56%, for the bare TiO₂, 2%, 5% and 10% Al‐doped TiO₂, respectively. It was found that 2 mol% of Al‐doped TiO₂ shows the best photocatalytic performance. In low concentration of dopant, separation of photogenerated electron–hole pairs promoted, and subsequently, the degradation efficiency increased. It was proposed that the degradation of RhB by 2 mol% Al‐doped TiO₂ photocatalyst follows both N‐deethylation and chromophore cleavage mechanisms, while the N‐deethylation still predominated over cleavage of dye chromophore structure. The key role of hydroxyl radicals in RhB degradation was verified by the effects of scavengers. In addition, the photocatalyst can be reused for three runs without any significant loss of its catalytic activity.     

Absolute stereochemical determination of chiral carboxylic acids

Monoamidation of 1,4-diaminobenzene with alpha-chiral carboxylic acids leads to a carrier strategy for absolute stereochemical determination with bis-zinc porphyrin tweezers by exciton-coupled circular dichroism (ECCD). The helicity induced in the porphyrin tweezers upon complexation with the derivatized carrier originates from the preferred conformation of the C(carbonyl)-C(chiral) bond. Correct ECCD signs can be predicted by the rotamer that places the large group perpendicular to the carbonyl group with the small group facing the porphyrin. [reaction: see text]     

Ultrasonic velocities, densities, viscosities, electrical conductivities, Raman spectra, and molecular dynamics simulations of aqueous solutions of Mg(OAc)2 and Mg(NO3)2: Hofmeister effects and ion pair formation

The ultrasonic velocities, densities, viscosities, and electrical conductivities of aqueous solutions of magnesium nitrate and magnesium acetate have been measured from dilute to saturation concentrations at 0 < or = t/degrees C < or = 50. The temperature derivative of the isentropic compressibility, kappa(s), became zero at 2.28 and 2.90 mol kg(-1) for Mg(OAc)2 and Mg(NO3)2 solutions, respectively, at 25 degrees C. The total hydration numbers of the dissolved ions were estimated to be, respectively, 24.3 and 19.2 at these concentrations. Differences in kappa(s) for various M2+ salts, using the present and literature data, correlated with reported M2+-OH2 bond lengths and to a lesser extent with cationic charge densities (ionic radii). The influence of anions on kappa(s) appears to follow the Hofmeister series and also correlates approximately with the anionic charge density. Substantial differences between Mg(OAc)2(aq) and Mg(NO3)2(aq) occur with respect to their structural relaxation times (derived from compressibility and viscosity data) and their electrical conductivities. These differences were attributed to a much greater ion association in Mg(OAc)2 solutions. Raman spectra recorded at 28 degrees C confirmed the presence of various types of contact ion pairs including mono- and bidentate complexes in Mg(OAc)2(aq). In Mg(NO3)2(aq), only noncontact ion pairs appear to be formed even at high concentrations. The experimental results are supported by molecular dynamics simulations, which also reveal the much stronger tendency of OAc- compared to NO3- to associate with Mg2+ in aqueous solutions. The simulations also allow an evaluation of the ion-ion and ion-water radial distribution functions and cumulative sums and provide a molecular picture of ion hydration in Mg(OAc)2(aq) and Mg(NO3)2(aq) at varying concentrations.