A system for low field imaging of laser-polarized noble gas

We describe a device for performing MRI with laser-polarized noble gas at low magnetic fields (<50 G). The system is robust, portable, inexpensive, and provides gas-phase imaging resolution comparable to that of high field clinical instruments. At 20.6 G, we have imaged laser-polarized (3)He (Larmor frequency of 67 kHz) in both sealed glass cells and excised rat lungs, using approximately 0.1 G/cm gradients to achieve approximately 1 mm(2) resolution. In addition, we measured (3)He T(2)(*) times greater than 100 ms in excised rat lungs, which is roughly 20 times longer than typical values observed at high ( approximately 2 T) fields. We include a discussion of the practical considerations for working at low magnetic fields and conclude with evidence of radiation damping in this system.     

Energetics and dynamics of decaying cluster ions

The recent addition of (i) a third sector field to our two sector field mass spectrometer (resulting in a BE1E2 field configuration) and of (ii) a high performance electron gun enables us now to study in detail the time dependence of the kinetic energy release distribution (KERD) over a relatively wide range of cluster ion lifetimes. Using this newly constructed device we have studied here for the first time KERDs and deduced binding energies BEs (using finite heat bath theory) of large rare gas cluster ions (an upper size limit in earlier studies arose from the fact that different naturally occurring isotopes will contribute to a chosen metastable peak when the size exceeds a certain value) and in addition of fullerene ions smaller and larger than (here again contaminating coincidences did not allow such studies earlier). Moreover, high precision KERD measurements for the decay of rare gas dimer ions in conjunction with model calculations (using recently calculated potential energy curves for the rare gas dimer ions) also enable us to obtain information on the dynamics and the mechanisms of the underlying spontaneous decay reactions . In addition, we are also reporting here a novel method (unified breakdown graph method) to determine cluster ion binding energies using a recently constructed tandem mass spectrometer BESTOF allowing us to measure fragmentation patterns arising from the unimolecular decay of molecular cluster ions induced by surface collisions. The fragmentation and reaction patterns of protonated ethanol cluster ions investigated here clearly demonstrate in contrast to some of the earlier cluster ion studies that unimolecular dissociation kinetics determines the formation of product ions in the surface-induced decomposition.     

Investigation of the trapping fraction for a coaxial accelerator

In this paper the trapping efficiency of the ionizing current sheath (snowplough) in a coaxial accelarator is investigated. It turns out that the trapping efficiency of the snowplough is in general a time dependent quantity and also depends on the initial neutral gas density and current.     

Study of gas-fluidization dynamics with laser-polarized 129Xe

We report initial NMR studies of gas dynamics in a particle bed fluidized by laser-polarized xenon (129Xe) gas. We have made preliminary measurements of two important characteristics: gas exchange between the bubble and emulsion phases and the gas velocity distribution in the bed. We used T2* contrast to differentiate the bubble and emulsion phases by choosing solid particles with large magnetic susceptibility. Experimental tests demonstrated that this method was successful in eliminating 129Xe magnetization in the emulsion phase, which enabled us to observe the time dependence of the bubble magnetization. By employing the pulsed field gradient method, we also measured the gas velocity distribution within the bed. These results clearly show the onset of bubbling and can be used to deduce information about gas and particle motion in the fluidized bed.     

Mineral?le

Ohne Zusammenfassung     

Alkaline Earth Diazapentadienyl Compounds: Structure of [Ba2{(C6H11)NC(Me)CHC(Me)N(C6H11)}3{(SiMe3)2N}]

Three different bonding modes in one molecule! The diazapentadienyl ligands in the title compound 1 adopt η¹,η¹-N,N-chelating plus η⁵-terminal, η¹η¹-N,N chelating plus η⁵-bridging, and novel η¹-N plus η³-1-aza-allyl bonding modes. R=cyclohexyl.     

Probing porous media with gas diffusion NMR.

We show that gas diffusion nuclear magnetic resonance (GD-NMR) provides a powerful technique for probing the structure of porous media. In random packs of glass beads, using both laser-polarized and thermally polarized xenon gas, we find that GD-NMR can accurately measure the pore space surface-area-to-volume ratio, S/V rho, and the tortuosity, alpha (the latter quantity being directly related to the system's transport properties). We also show that GD-NMR provides a good measure of the tortuosity of sandstone and complex carbonate rocks.     

Hydrophilic surface modification of cyclic olefin copolymer microfluidic chips using sequential photografting

The plastic material known as cyclic olefin copolymer (COC) is a useful substrate material for fabricating microfluidic devices due to its low cost, ease of fabrication, excellent optical properties, and resistance to many solvents. However, the hydrophobicity of native COC limits its use in bioanalytical applications. To increase surface hydrophilicity and reduce protein adsorption, COC surfaces were photografted with poly(ethylene glycol) methacrylate (PEGMA) using a two-step sequential approach: covalently-bound surface initiators were formed in the first step and graft polymerization of PEGMA was then carried out from these sites in the second step. Contact angle measurements were used to monitor and quantify the changes in surface hydrophilicity as a function of grafting conditions. As water droplet contact angles decreased from 88 degrees for native COC to 45 degrees for PEGMA-grafted surfaces, protein adsorption was also reduced by 78% for the PEGMA-modified COC microchannels as determined by a fluorescence assay. This photografting technique should enable the use of COC microdevices in a variety of bioanalytical applications that require minimal nonspecific adsorption of biomolecules.     

Acoustic Propulsion of Nanorod Motors Inside Living Cells

The ultrasonic propulsion of rod‐shaped nanomotors inside living HeLa cells is demonstrated. These nanomotors (gold rods about 300 nm in diameter and about 3 μm long) attach strongly to the external surface of the cells, and are readily internalized by incubation with the cells for periods longer than 24 h. Once inside the cells, the nanorod motors can be activated by resonant ultrasound operating at 4 MHz, and show axial propulsion as well as spinning. The intracellular propulsion does not involve chemical fuels or high‐power ultrasound and the HeLa cells remain viable. Ultrasonic propulsion of nanomotors may thus provide a new tool for probing the response of living cells to internal mechanical excitation, for controllably manipulating intracellular organelles, and for biomedical applications.