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Pulse Application (pulse + application)

Distribution by Scientific Domains

Medical Sciences	50%

Selected Abstracts

Phosphorus uptake, not carbon transfer, explains arbuscular mycorrhizal enhancement of Centaurea maculosa in the presence of native grassland species

FUNCTIONAL ECOLOGY, Issue 6 2002
C. A. Zabinski
Summary 1Previous studies have shown that arbuscular mycorrhizas (AM) enhance the growth of the invasive forb Centaurea maculosa when growing with native grass species. Using 13CO2, we tested the hypothesis that this enhancement is explained by carbon transfer from native species to C. maculosa via mycorrhizal hyphal linkages. 2A C. maculosa plant was paired with one of five native species , three grasses (Festuca idahoensis, Koeleria cristata and Pseudoroegneria spicata) and two forbs (Achillea millefolium and Gaillardia aristata) , in pots that separated the plants with either a mesh barrier (28 µm, excludes fine roots but not hyphae) or a membrane barrier (0·45 µm, excludes roots and hyphae). 313CO2 was added to the atmosphere of either Centaurea or the native species after 20 weeks' growth. A 25 min pulse application was followed by 7 days' growth and subsequent harvest. 4The biomass response of C. maculosa was consistent with previous experiments: C. maculosa was larger when growing in mesh barrier pots, when hyphae were able to access the opposite side of the pot; in mesh barrier pots only, biomass varied with neighbouring species. Native plant biomass did not vary between mesh- vs membrane-barrier pots. 5There was no evidence of carbon transfer, either from the native plant to C. maculosa or in the reverse direction. 6Centaurea maculosa contained significantly more phosphorus in mesh-divided pots, but this depended on the neighbouring plant. The P concentration in C. maculosa was significantly higher in mesh-divided pots when growing with a grass and not a forb. Native species contained more P in mesh-divided pots than membrane-divided pots, and P concentration differed between species (higher in forbs than grasses), but did not vary between mesh- and membrane-divided pots. 7Our study suggests that C. maculosa is able to exploit its mycorrhizal symbiosis more effectively than the native grassland species. The mechanism for this appears to be luxury consumption of P through efficient utilization of extra-radical hyphae, but that effect is dependent on neighbouring species, and occurs when growing with a grass neighbour. 8Although no single study can disprove the carbon-transfer hypothesis, our work suggests that AM-mediated neighbour effects are the result of mycorrhizal networks that increase species' access to P. Whether the synergistic effects of neighbours are due to complementarity of AM fungal symbionts utilized by different plant species, or have to do with the structure of AM networks that develop more extensively with multiple host plants, remains to be investigated. [source]

Improvement of vessel visibility in time-of-flight MR angiography of the brain

JOURNAL OF MAGNETIC RESONANCE IMAGING, Issue 6 2008
Takaharu Shonai MD
Abstract Purpose To improve vessel visibility in time-of-flight MR angiography (TOF-MRA) by careful consideration of coil choice, coil position, and frequency offset and profile of the nonspatially selective chemical shift selective (CHESS) presaturation pulse. Materials and Methods The effects of both the CHESS and the excitation radiofrequency (RF) pulses on flow signal and signals from stationary substances were evaluated by changing the spatial area where RF pulses were applied to upstream flow in a flow phantom and in human subjects. The difference between the eight-channel phased-array receive-only coil and the transmit,receive coil was evaluated. Results The CHESS pulse suppresses the flow signal over a wider frequency range than the signals from stationary substances, especially when using the body coil for transmission. Even without presaturation pulse, the excitation pulse slightly suppressed the flow signal. Adjusting the position of the transmit,receive coil relative to the head improved these TOF-MRA images. The results were better than those obtained with the eight-channel coil. Conclusion The excitation and the nonspatially selective CHESS pulses degraded the flow signal. Our results suggest that reduced spatial extent of RF pulse application to upstream flow can improve image quality of TOF-MRA. This result can be implemented on conventional scanners. J. Magn. Reson. Imaging 2008;27:1362,1370. © 2008 Wiley-Liss, Inc. [source]

Histologic evaluation of skin damage after overlapping and nonoverlapping flashlamp pumped pulsed dye laser pulses: A study on normal human skin as a model for port wine stains

LASERS IN SURGERY AND MEDICINE, Issue 2 2001
Petra H.L. Koster MD
Abstract Background and Objective In the treatment of port wine stains (PWS) with the flashlamp pumped pulsed dye laser (FPPDL), no consensus exists about overlapping of pulses. The advantage of overlapping pulses is homogeneous lightening of the PWS; the risk is redundant tissue damage. The aim of this study was to determine the histopathologic effect on human skin of pulsed dye laser pulses with various degrees of overlap, with normal human skin as a model for PWS. Study Design/Materials and Methods Eighteen healthy white volunteers were irradiated with pulsed dye laser pulses with increasing radiant exposure and with different degrees of overlap. Biopsy samples were taken and histologically analysed. Results Overlapping of pulses on normal human skin enhances depth of vascular damage with approximately 30%. Adjacent pulses also show this effect. We found no histologic signs of serious damage to epidermis or dermal connective tissue by using radiant exposure levels of 6,8 J/cm2, regardless of pulse application. Conclusions Reasoning that the mechanism of tissue injury is comparable for normal and PWS skin, we conclude that it is safe to treat PWS with overlapping FPPDL pulses to achieve homogeneous lightening. Lasers Surg. Med. 28:176,181, 2001. © 2001 Wiley-Liss, Inc. [source]

Photoinduced nonequilibrium spin, charge polarizations and spin-dependent current in quantum rings

PHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 3 2010
Z. G. Zhu
Abstract We investigate the spin-dependent dynamical response of a semiconductor quantum ring with a spin orbit interaction upon the application of a single and two linearly polarized, picosecond, asymmetric electromagnetic pulses in the presence of a static magnetic flux. We find that the pulse-generated electric dipole moment is spin dependent. It is also shown that the spin orbit interaction induces an extra SU(2) effective flux in addition to the static external magnetic flux which is reflected in an additional periodicity of the spin-dependent dipole moment. Furthermore, the pulses may induce a net dynamical charge currents and dynamical spin currents when the clockwise and anti-clockwise symmetry of the carrier is broken upon the pulse application. [source]