Rapid acquisition strategy for functional T1ρ mapping of the brain

Functional T1ρ mapping has been proposed as a method to assess pH and metabolism dynamics in the brain with high spatial and temporal resolution. The purpose of this work is to describe and evaluate a variant of the spin-locked echo-planar imaging sequence for functional T1ρ mapping at 3 T. The proposed sequence rapidly acquires a time series of T1ρ maps with 4.0 second temporal resolution and 10 slices of volumetric coverage. Simulation, phantom, and in vivo experiments are used to evaluate many aspects of the sequence and its implementation including fidelity of measured T1ρ dynamics, potential confounds to the T1ρ response, imaging parameter tradeoffs, time series analysis approaches, and differences compared to blood oxygen level dependent functional magnetic resonance imaging. It is shown that the high temporal resolution and volumetric coverage of the sequence are obtained with some expense including underestimation of the T1ρ response, sensitivity to T1 dynamics, and reduced signal-to-noise ratio. In vivo studies using a flashing checkerboard functional magnetic resonance imaging paradigm suggest differences between T1ρ and blood oxygen level dependent activation patterns. Possible sources of the functional T1ρ response and potential sequence improvements are discussed. The capability of T1ρ to map whole-brain pH and metabolism dynamics with high temporal and spatial resolution is potentially unique and warrants further investigation and development.     

A Comment on the Formation of Objective Response Functions

The well-known method for obtaining objective response functions in continuum mechanics, due to W. Noll, is reviewed and an objection to its logic, raised by R.S. Rivlin and G.F. Smith, is evaluated.     

In situ temperature-jump dynamic nuclear polarization: enhanced sensitivity in two dimensional 13C-13C correlation spectroscopy in solution

Dynamic nuclear polarization is combined with temperature-jump methods to develop a new 2D 13C-13C NMR experiment that yields a factor of 100-170 increase in sensitivity. The polaization step is performed at 100 K, and the sample is subsequently melted with a 10.6 microm laser pulse to yield a sample with highly polarized 13C spins. 13C detected 2D 13C-13C spectroscopy is performed in the usual manner.     

Observation of solid-state 103Rh NMR by cross-polarization

Using 103Rh[1H] cross-polarization (CP) methods, we have obtained solid-state 103Rh NMR spectra for diamagnetic Rh(III) compounds. The isotropic chemical shift and chemical shift anisotropy (CSA) are reported for a crystalline form of the dihydroxy-bridged Rh(III) dimer and for a salt of the oxo-centered acetate-bridged Rh(III) trimer, from analysis of conventional CP/MAS spectra. Comparison of the CP kinetics of the dimer with new crystal structure data suggests a strategy for predicting 103Rh CP/MAS properties in solids.     

The combined effect of spatial compounding and nonlinear filtering on the speckle reduction in ultrasound images

Recently, a spatial compounding ultrasound imaging method was presented that utilizes a conventional 64-element phased array transducer with two unfocused pistons, each placed at one of the sides of the phased array transducer. This method is augmented here by inclusion of nonlinear filtering of the compounded images. The combined effects of the specific spatial compounding and nonlinear filtering on speckle reduction in the generated ultrasound images are studied and evaluated in two stages: First, the image quality is studied when nonlinear filtering is used as part of the spatial compounding. The study is performed by simulations using the Field II program, by processing several B-mode images of a kidney. The second stage compares the results obtained by the simulations to those obtained by in vitro laboratory experiments. Five different compounding strategies and two nonlinear filters, Gaussian and anisotropic diffusion, are investigated and evaluated in terms of image quality parameters-contrast and signal-to-noise ratio. It is shown that the combination of "averaging+nonlinear Gaussian filtering" produces the greatest improvement of image quality. When compared to a conventional phased array imaging system, the spatial compounding method that includes the conventional 64-element phased array transducer with two unfocused pistons, and employs the "averaging+nonlinear Gaussian filtering" strategy, obtains improvement in SNR that has reached 334%. Thus, though this method necessitates a somewhat wider probe, it produces significantly improved images.     

A molecular dynamics investigation of hydrolytic polymerization in a metal-hydroxide gel

The early stages of the spontaneous hydrolytic polymerization of an active hydroxide in the anti-bayerite structure are followed by using molecular dynamics simulations. The polymer populations are calculated as a function of reaction progress and compared with a model governed by purely random bonding. In agreement with experimental observations in aqueous solutions, the transformation of singly bridged to doubly bridged metal ions is shown to have a significant autocatalytic component. The overall polymer populations, however, are very close to the predictions of the random bonding model, indicating that local autocatalytic behavior is decoupled from multimer populations at the larger scales. The calculations show that solid-state transformation processes do not preferentially give rise to higher order multimers, and suggest that interfacial processes, involving bulk solution, are required to facilitate rapid transformation to higher order oligomers. Two reaction pathways are identified for the dewatering of mu-H(3)O(2) bridges into mu-OH bridges. Both are activated primarily by undercoordination of one of the metals centers involved in the bridge.     

Optimising container storage processes at multimodal terminals

Multimodal Container Terminals (MMCT) require comprehensive planning, programming and control in order to operate an efficient storage system. In this paper, a model has been developed for the storage system of the MMCT. It is an extension of the Blocks Relocation Problem, with incoming as well as outgoing containers, or ‘blocks’. The model deals with assigning containers to positions within the storage area, rehandling of containers to be retrieved, and calculation of the processing times in order to perform these actions. A number of constructive heuristics are presented in order to produce good initial solutions for this problem. Meta-heuristics are also used to improve on these solutions. Results from the various heuristics on a few case study problems are compared and discussed. This research will also provide a core piece of technology for the development of autonomous container handling systems for terminals.     

The electronic spectrum of tantalum hydride and deuteride

The diatomic molecule tantalum hydride (TaH) and its isotopologue tantalum deuteride (TaD) have been detected for the first time by laser excitation spectroscopy. The gas-phase molecules were produced in a hollow cathode discharge. Two red-degraded bands, one arising from TaH at 636 nm and the other from TaD at 635 nm, have been recorded at sub-Doppler resolution by intermodulated fluorescence spectroscopy. A rotational analysis shows that both bands are Ω = 2←2 in character, with well-resolved Ω-doubling in the upper state of TaH. Analysis of the ¹⁸¹Ta magnetic dipole and electric quadrupole hyperfine structure reveals that the lower X³Φ₂ electronic state of the two transitions arises from a σ²πδ electronic configuration, in agreement with previous theoretical calculations. The bond length in the TaH X³Φ₂ (v = 0) level is found to be 1.756960(4) Å.