189 research outputs found
Colloidal templating at a cholesteric - oil interface: Assembly guided by an array of disclination lines
We simulate colloids (radius m) trapped at the interface between
a cholesteric liquid crystal and an immiscible oil, at which the helical order
(pitch p) in the bulk conflicts with the orientation induced at the interface,
stabilizing an ordered array of disclinations. For weak anchoring strength W of
the director field at the colloidal surface, this creates a template, favoring
particle positions eitheron top of or midway between defect lines, depending on
. For small , optical microscopy experiments confirm this
picture, but for larger no templating is seen. This may stem from the
emergence at moderate W of a rugged energy landscape associated with defect
reconnections.Comment: 5 pages, 4 figure
Structural Elucidation of Amorphous Photocatalytic Polymers from Dynamic Nuclear Polarization Enhanced Solid State NMR
Dynamic nuclear polarization (DNP) solid-state nuclear magnetic resonance (NMR) offers a recent approach to dramatically enhance NMR signals and has enabled detailed structural information to be obtained in a series of amorphous photocatalytic copolymers of alternating pyrene and benzene monomer units, the structures of which cannot be reliably established by other spectroscopic or analytical techniques. Large 13C cross-polarization (CP) magic angle spinning (MAS) signal enhancements were obtained at high magnetic fields (9.4â14.1 T) and low temperature (110â120 K), permitting the acquisition of a 13C INADEQUATE spectrum at natural abundance and facilitating complete spectral assignments, including when small amounts of specific monomers are present. The high 13C signal-to-noise ratios obtained are harnessed to record quantitative multiple contact CP NMR data, used to determine the polymersâ composition. This correlates well with the putative pyrene:benzene stoichiometry from the monomer feed ratio, enabling their structures to be understood
Histological evaluation of a cochlear implant electrode array with electrically activated shape change for perimodiolar positioning
For the treatment of deafness or severe hearing loss cochlear implants (CI) are used to stimulate the auditory nerve of the inner ear. In order to produce an electrode array which is both atraumatic and reaches a perimodiolar final position a design featuring shape memory effect was proposed. A Nitinol wire with a diameter of 100 ÎŒm was integrated in a state of the art lateral wall electrode array. The wire serves as an actuator after it has been âtrainedâ to adopt the spiral shape of an average human cochlea. Three small diameter platinum-iridium wires (each 20 ÎŒm) were crimped to the Nitinol wire in order to produce thermal energy. An insertion test was pursued using a human temporal bone specimen. The prototype electrode array was cooled down by means of immersion in ice water and freeze spray to enable sufficient straightening. Thereafter, insertion into the cochlea through the round window as performed. Insertion was feasible but difficult as premature curling of the electrode occurred during the movement towards the inner ear while passing the middle ear cavity. Therefore, the insertion had to be performed faster than usual. The shape memory actuator was subsequently activated with 450mA current at 5V for 3 seconds. After insertion the specimen was embedded in epoxy resin, microgrinded and all histological slices were assessed for trauma. Perimodiolar position was achieved. No insertion trauma was observed and there were no indications of thermal damage caused by the electrical heating. To the best of our knowledge, this is the first histological evaluation of the insertion trauma caused by an electrically activated shape memory electrode array. These promising results support further research on shape memory CI electrode arrays
The 74MHz System on the Very Large Array
The Naval Research Laboratory and the National Radio Astronomy Observatory
completed implementation of a low frequency capability on the VLA at 73.8 MHz
in 1998. This frequency band offers unprecedented sensitivity (~25 mJy/beam)
and resolution (~25 arcsec) for low-frequency observations. We review the
hardware, the calibration and imaging strategies, comparing them to those at
higher frequencies, including aspects of interference excision and wide-field
imaging. Ionospheric phase fluctuations pose the major difficulty in
calibrating the array. Over restricted fields of view or at times of extremely
quiescent ionospheric ``weather'', an angle-invariant calibration strategy can
be used. In this approach a single phase correction is devised for each
antenna, typically via self-calibration. Over larger fields of view or at times
of more normal ionospheric ``weather'' when the ionospheric isoplanatic patch
size is smaller than the field of view, we adopt a field-based strategy in
which the phase correction depends upon location within the field of view. This
second calibration strategy was implemented by modeling the ionosphere above
the array using Zernike polynomials. Images of 3C sources of moderate strength
are provided as examples of routine, angle-invariant calibration and imaging.
Flux density measurements indicate that the 74 MHz flux scale at the VLA is
stable to a few percent, and tied to the Baars et al. value of Cygnus A at the
5 percent level. We also present an example of a wide-field image, devoid of
bright objects and containing hundreds of weaker sources, constructed from the
field-based calibration. We close with a summary of lessons the 74 MHz system
offers as a model for new and developing low-frequency telescopes. (Abridged)Comment: 73 pages, 46 jpeg figures, to appear in ApJ
Recommended from our members
Gemini Principles
Up to 30% of annual spend across the built environment is lost in inefficiencies related to poor quality data1. This is seen in lost productivity due to underperforming economic and social infrastructure. Effective information management will enable better decisions, leading to financial savings, improved performance and service, and better outcomes for business and society per whole-life pound. To make this possible an information management framework is necessary.
This paper seeks to build consensus on foundational definitions and guiding values â the Gemini Principles â and to begin enabling alignment on the approach to information management across the built environment.Funded by the Centre for Digital Built Britai
Milestones in the Observations of Cosmic Magnetic Fields
Magnetic fields are observed everywhere in the universe. In this review, we
concentrate on the observational aspects of the magnetic fields of Galactic and
extragalactic objects. Readers can follow the milestones in the observations of
cosmic magnetic fields obtained from the most important tracers of magnetic
fields, namely, the star-light polarization, the Zeeman effect, the rotation
measures (RMs, hereafter) of extragalactic radio sources, the pulsar RMs, radio
polarization observations, as well as the newly implemented sub-mm and mm
polarization capabilities.
(Another long paragraph is omitted due to the limited space here)Comment: Invited Review (ChJA&A); 32 pages. Sorry if your significant
contributions in this area were not mentioned. Published pdf & ps files (with
high quality figures) now availble at http://www.chjaa.org/2002_2_4.ht
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