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Parallel-detection electron energy loss spectroscopy (EELS) in the scanning transmission electron microscope provides a very sensitive means of detecting specific elements in biological systems. By analyzing EELS spectrum-image data recorded from rapidly-frozen and cryosectioned tissue it is possible to map quantitatively the distribution of the biologically important element, calcium, which is typically present at concentrations of only a few parts per million in cellular structures some tens of nanometers in diameter. A significant improvement (factor of four) in calcium detectability has been demonstrated for EELS compared with energy-dispersive x-ray spectroscopy. The spectrum-imaging technique has also been applied to map water distributions in hydrated biological specimens by utilizing the valence electron excitations.
The Petawatt laser at Lawrence Livermore National
Laboratory (LLNL) has opened a new regime of laser matter
interactions in which the quiver motion of plasma electrons
is fully relativistic with energies extending well above
the threshold for nuclear processes. In addition to ∼few
MeV ponderomotive electrons produced in ultra intense laser-solid
interactions, we have found a high energy component of
electrons extending to ∼100 MeV apparently from relativistic
selffocusing and plasma acceleration in the underdense
preformed plasma. The generation of hard bremsstrahlung,
photonuclear reactions, and preliminary evidence for positron-electron
pair production will be discussed.
Continuous Plankton Recorder records from the North Sea and north-east Atlantic from September 1997 to March 1998 indicate an exceptional influx of oceanic indicator species into the North Sea. These inflow events, according to historical evidence, have only occurred sporadically during this century. This exceptional inflow and previous inflow events are discussed in relation to their similarity in terms of their physical and climatic conditions.
Compositional imaging with electron energy loss spectroscopy
(EELS) can be performed in both the energy-filtering transmission
electron microscope (EFTEM) and in the scanning transmission
electron microscope (STEM). Quantitative elemental distributions
are obtained from core-edges produced by inner-shell excitations,
although more detailed information about chemical bonding and
electronic structure is also available from the fine structure
associated with valence electron excitations. The fixed-beam
EFTEM can provide data from large numbers of pixels very rapidly
and offers an advantage for analysis of extended specimen regions
containing relatively high atomic concentrations. Acquisition
of entire spectra at each pixel in the field-emission STEM
(spectrum-imaging technique) provides improved flexibility and
accuracy despite the longer recording times. Spectrum-imaging
allows post facto data processing with parameters that
can be varied after acquisition is completed. In suitably thin
specimens, EELS compositional mapping can provide a sensitivity
of a few atoms for certain elements.
Doliolids were found in samples taken with a Continuous Plankton Recorder (CPR) in October 1989 between 55°14'N 03°32'E and 55°20'N 06°13'E during a tow between Newcastle and Esbjerg. Densities were estimated at >100 m−3 for about 112 km of tow. A sub-sample of specimens in sufficiently good condition to be reliably identified were referred to Doliolum nationalis Borgert. Substantial numbers of doliolids were found on a CPR tow between Harwich and Gothenburg which passed through the same area in that month and specimens were found nearer to the Danish coast in November and south-west of Helgoland in December. The distribution of doliolids in CPR samples taken in the North Sea in the last three months of 1989 is shown in Figure 1.
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