Evidence of dispersion in an artificial water-saturated sand sediment

A laboratory experiment was conducted to measure the speed of sound in an artificial water-saturated granular sediment composed of cleaned and sorted medium-grained sand and degassed distilled water. The experiment was conducted within a range of frequencies where dispersion is predicted by a number of existing models. Between 2 and 4 kHz, the sound speed was inferred from measurements of the resonance frequencies of a thin-walled cylindrical container filled with the material. An elastic waveguide model was used to account for the effect of the finite impedance of the walls, although this effect was found to be small. From 20 to 300 kHz, the sound speed was obtained directly from time-of-flight measurements within the sediment. Dispersion in close agreement with the Williams effective density fluid model [K. L. Williams, J. Acoust. Soc. Am. 110, 2276-2281 (2001)] was observed.     

Solvation of Calcium–Phosphate Headgroup Complexes at the DPPC/Aqueous Interface

The effects of sodium (Na⁺) and calcium (Ca²⁺) cations on model zwitterionic dipalmitoylphosphatidylcholine (DPPC) monolayers spread on metal chloride salt solutions are investigated by means of vibrational sum frequency generation (VSFG) and heterodyne‐detected (HD)‐VSFG spectroscopy. VSFG and HD‐VSFG spectra in the OH stretching region reveal cation‐specific effects on the interfacial water′s H‐bonding network, knowledge of which has been limited to date. It is found that low‐concentrated Ca²⁺ more strongly perturbs interfacial water organization relative to highly concentrated Na⁺. At higher Ca²⁺ concentrations, the water H‐bonding network at the DPPC/CaCl₂ interface reorganizes and the resulting spectrum closely follows that of the bare air/CaCl₂ interface up to ～3400 cm^?1. Most interesting is the appearance of a negative band at ～3450 cm^?1 in the DPPC/CaCl₂ Im χ_s⁽²⁾ spectra, likely arising from an asymmetric solvation of Ca²⁺–phosphate headgroup complexes. This gives rise to an electric field that orients the net OH transition moments of a subset of OH dipoles toward the bulk solution.     

Fast functional brain signal changes detected by diffusion weighted fMRI

Functional magnetic resonance imaging (fMRI) has become the method of choice in the study of system neuroscience, as evidenced by an explosion of such literature in the past decade. Contrast mechanisms based on the blood oxygenation level, volume, and flow changes have been used to non-invasively detect brain activation secondary to the neuronal activity. However, because of the hemodynamic modulations inherent in these signals, their spatial and temporal characteristics are influenced by the complex geometry and varying delivery speed of the brain vasculature. Consequently, spatial dispersions and temporal delays are commonly seen in the brain activity using fMRI. It is thus of critical importance to investigate alternative contrast mechanisms that may offer shorter temporal delays and more direct spatial localization. In light of a recent phantom study which demonstrated the possibility to detect the destructive phase addition from the spatially incoherent, yet temporally synchronized, displacements caused by the Lorentz force experienced during electrical conduction within a strong magnetic field, we seek to apply similar imaging technique to investigate the functional signal changes that may provide alternative temporal and spatial characteristics. It is found that by using heavy diffusion weighting, which is one form of displacement encoding strategies, to remove the vascular signal and sensitize the minute and incoherent displacement, one can detect fast dynamic signal changes synchronized to the task. This finding may help take an initial step toward direct non-invasive MRI detection of the neuronal activity with improved temporal accuracy.     

Identification of I3 − and I5 − clusters in irradiated ki by X-ray photoelectron,Raman and optical absorption spectroscopies

Abstract

Raman and XPS measurements have been performed on KI crystals irradiated near 200 K. The Raman studies show I₃ ^? and I_n ^? (n = 5, 7,—) clusters which anneal together with F- and V- centres at 338 K. A small development of (I₂)_n aggregates occurs during the anneal; these decay near 378 K and are responsible for a broad and weak residual V-band. The I 3d _5/2 XPS peak has been fitted to reveal the presence of 3 components after low energy argon- ion bombardment. These are identified as due to normal lattice iodine, I₃ ^? and 1₅ ^? whose behaviour is consistent with the Raman work.     

Schur indices of association schemes

In this paper we introduce and investigate the theory of Schur indices arising from simple components of the rational adjacency algebras of association schemes and investigate methods for computing these indices.     

Fine-scale functional connectivity in somatosensory cortex revealed by high-resolution fMRI

High-resolution functional magnetic resonance imaging (fMRI) at high field (9.4 T) has been used to measure functional connectivity between subregions within the primary somatosensory (SI) cortex of the squirrel monkey brain. The hand-face region within the SI cortex of the squirrel monkey has been previously well mapped with functional imaging and electrophysiological and anatomical methods, and the orderly topographic map of the hand region is characterized by a lateral to medial representation of individual digits in four subregions of areas 3a, 3b, 1 and 2. With submillimeter resolution, we are able to detect not only the separate islands of activation corresponding to vibrotactile stimulations of single digits but also, in subsequent acquisitions, the degree of correlation between voxels within the SI cortex in the resting state. The results suggest that connectivity patterns are very similar to stimulus-driven distributions of activity and that connectivity varies on the scale of millimeters within the same primary region. Connectivity strength is not a reflection of global larger-scale changes in blood flow and is not directly dependent on distance between regions. Preliminary electrophysiological recordings agree well with the fMRI data. In human studies at 7 T, high-resolution fMRI may also be used to identify the same subregions and assess responses to sensory as well as painful stimuli, and to measure connectivity dynamically before and after such stimulations.     

Semirigid aromatic sulfone-carboxylate molecule for dynamic coordination networks: multiple substitutions of the ancillary ligands

We report dynamic, multiple single-crystal to single-crystal transformations of a coordination network system based on a semirigid molecule, TCPSB = 1,3,5-tri(4'-carboxyphenylsulphonyl)benzene, which nicely balances shape persistence and flexibility to bring about the framework dynamics in the solid state. The networks here generally consist of (1) the persistent core component (denoted as CoTCPSB) of linear Co(II) aqua clusters (Co-O-Co-O-Co) integrated into 2D grids by 4,4'-bipyridine and TCPSB and (2) ancillary ligands (AL) on the two terminal Co(II) ions-these include DMF (N,N'-dimethylformamide), DMA (N,N'-dimethylacetamide), CH(3)CN, and water. Most notably, the ancillary ligand sites are highly variable and undergo multiple substitution sequences while maintaining the solid reactants/products as single-crystals amenable to X-ray structure determinations. For example, when immersed in CH(3)CN, the AL of an as-made single crystal of CoTCPSB-DMF (i.e., DMF being the AL) is replaced to form CoTCPSB-CH(3)CN, which, in air, readily loses CH(3)CN to form CoTCPSB-H(2)O; the CoTCPSB-H(2)O single crystals, when placed in DMF, give back CoTCPSB-DMF in single-crystal form. Other selective, dynamic exchanges include the following: CoTCPSB-DMF reacts with CH(3)CN (to form CoTCPSB-CH(3)CN) but NOT with water, methanol, ethanol, DMA, or pyridine; CoTCPSB-H(2)O specifically pick outs DMF from a mixture of DMF, DMA, and DEF; an amorphous, dehydrated solid from CoTCPSB-H(2)O regains crystalline order simply by immersion in DMF (to form CoTCPSB-DMF). Further exploration with functional, semirigid ligands like TCPSB shall continue to uncover a wider array of advanced dynamic behaviors in solid state materials.     

Development of a new consumable-free thermal modulator for comprehensive two-dimensional gas chromatography

A simple and cost-effective GC × GC modulator requiring no moving parts or consumables, hence suitable for field analysis and monitoring, was developed. The modulator was constructed from a specially designed Silcosteel^® trapping capillary, installed outside the GC oven, and coated inside with polydimethylsiloxane (PDMS) stationary phase. Dual-stage modulation was accomplished by resistively heating alternate segments of the trap with a custom-designed capacitive discharge power supply. The performance of the proposed modulator was comparable to many GC × GC systems currently in use, with the injection band widths as low as 60 ms at half height. With proper selection of the stationary phase in the trap, the modulator can be used for the analysis of complex mixtures with volatility range spanning from n-C5 to n-C40.