180 research outputs found
Oxidative ring expansion of a low-coordinate palladacycle : synthesis of a robust T-shaped alkylpalladium(II) complex
The synthesis of an unusual T-shaped alkylpalladium(II) complex featuring a cyclometalated tri-tert-butylphosphineoxide ligand by oxidation of the corresponding cyclometalated tri-tert-butylphosphine complex with PhIO is reported. We speculate that this reaction proceeds by formation of a transient palladium oxo intermediate and there are structural similarities with a late transition metal exemplar: Milstein’s seminal pincer ligated Pt(IV) oxo (Nature 2008, 455, 1093–1096)
A micro-optical module for multi-wavelength addressing of trapped ions
The control of large-scale quantum information processors based on arrays of
trapped ions requires a means to route and focus multiple laser beams to each
of many trapping sites in parallel. Here, we combine arrays of fibres, 3D
laser-written waveguides and diffractive microlenses to demonstrate the
principle of a micro-optic interconnect suited to this task. The module is
intended for use with an ion microtrap of 3D electrode geometry. It guides ten
independent laser beams with unique trajectories to illuminate a pair of
spatially separated target points. Three blue and two infrared beams converge
to overlap precisely at each desired position. Typical relative crosstalk
intensities in the blue are and the average insertion loss
across all channels is dB. The module occupies times less
volume than a conventional bulk-optic equivalent and is suited to different ion
species
Shift invariant preduals of ℓ<sub>1</sub>(ℤ)
The Banach space ℓ<sub>1</sub>(ℤ) admits many non-isomorphic preduals, for
example, C(K) for any compact countable space K, along with many more
exotic Banach spaces. In this paper, we impose an extra condition: the predual
must make the bilateral shift on ℓ<sub>1</sub>(ℤ) weak<sup>*</sup>-continuous. This is
equivalent to making the natural convolution multiplication on ℓ<sub>1</sub>(ℤ)
separately weak*-continuous and so turning ℓ<sub>1</sub>(ℤ) into a dual Banach
algebra. We call such preduals <i>shift-invariant</i>. It is known that the
only shift-invariant predual arising from the standard duality between C<sub>0</sub>(K)
(for countable locally compact K) and ℓ<sub>1</sub>(ℤ) is c<sub>0</sub>(ℤ). We provide
an explicit construction of an uncountable family of distinct preduals which do
make the bilateral shift weak<sup>*</sup>-continuous. Using Szlenk index arguments, we
show that merely as Banach spaces, these are all isomorphic to c<sub>0</sub>. We then
build some theory to study such preduals, showing that they arise from certain
semigroup compactifications of ℤ. This allows us to produce a large number
of other examples, including non-isometric preduals, and preduals which are not
Banach space isomorphic to c<sub>0</sub>
Evolution of opinions on social networks in the presence of competing committed groups
Public opinion is often affected by the presence of committed groups of
individuals dedicated to competing points of view. Using a model of pairwise
social influence, we study how the presence of such groups within social
networks affects the outcome and the speed of evolution of the overall opinion
on the network. Earlier work indicated that a single committed group within a
dense social network can cause the entire network to quickly adopt the group's
opinion (in times scaling logarithmically with the network size), so long as
the committed group constitutes more than about 10% of the population (with the
findings being qualitatively similar for sparse networks as well). Here we
study the more general case of opinion evolution when two groups committed to
distinct, competing opinions and , and constituting fractions and
of the total population respectively, are present in the network. We show
for stylized social networks (including Erd\H{o}s-R\'enyi random graphs and
Barab\'asi-Albert scale-free networks) that the phase diagram of this system in
parameter space consists of two regions, one where two stable
steady-states coexist, and the remaining where only a single stable
steady-state exists. These two regions are separated by two fold-bifurcation
(spinodal) lines which meet tangentially and terminate at a cusp (critical
point). We provide further insights to the phase diagram and to the nature of
the underlying phase transitions by investigating the model on infinite
(mean-field limit), finite complete graphs and finite sparse networks. For the
latter case, we also derive the scaling exponent associated with the
exponential growth of switching times as a function of the distance from the
critical point.Comment: 23 pages: 15 pages + 7 figures (main text), 8 pages + 1 figure + 1
table (supplementary info
Density-driven structural transformations in B2O3 glass
The method of in situ high-pressure neutron diffraction is used to investigate the structure of B2O3 glass on compression in the range from ambient to 17.5(5) GPa. The experimental results are supplemented by molecular dynamics simulations made using a newly developed aspherical ion model. The results tie together those obtained from other experimental techniques to reveal three densification regimes. In the first, BO3 triangles are the predominant structural motifs as the pressure is increased from ambient to 6.3(5) GPa, but there is an alteration to the intermediate range order which is associated with the dissolution of boroxol rings. In the second, BO4 motifs replace BO3 triangles at pressures beyond 6.3 GPa and the dissolution of boroxol rings continues until it is completed at 11–14 GPa. In the third, the B-O coordination number continues to increase with pressure to give a predominantly tetrahedral glass, a process that is completed at a pressure in excess of 22.5 GPa. On recovery of the glass to ambient from a pressure of 8.2 GPa, triangular BO3 motifs are recovered but, relative to the uncompressed material, there is a change to the intermediate range order. The comparison between experiment and simulation shows that the aspherical ion model is able to provide results of unprecedented accuracy at pressures up to at least 10 GPa
Instrumental performance and results from testing of the BLAST-TNG receiver, submillimeter optics, and MKID arrays
Polarized thermal emission from interstellar dust grains can be used to map
magnetic fields in star forming molecular clouds and the diffuse interstellar
medium (ISM). The Balloon-borne Large Aperture Submillimeter Telescope for
Polarimetry (BLASTPol) flew from Antarctica in 2010 and 2012 and produced
degree-scale polarization maps of several nearby molecular clouds with
arcminute resolution. The success of BLASTPol has motivated a next-generation
instrument, BLAST-TNG, which will use more than 3000 linear polarization
sensitive microwave kinetic inductance detectors (MKIDs) combined with a 2.5m
diameter carbon fiber primary mirror to make diffraction-limited observations
at 250, 350, and 500 m. With 16 times the mapping speed of BLASTPol,
sub-arcminute resolution, and a longer flight time, BLAST-TNG will be able to
examine nearby molecular clouds and the diffuse galactic dust polarization
spectrum in unprecedented detail. The 250 m detector array has been
integrated into the new cryogenic receiver, and is undergoing testing to
establish the optical and polarization characteristics of the instrument.
BLAST-TNG will demonstrate the effectiveness of kilo-pixel MKID arrays for
applications in submillimeter astronomy. BLAST-TNG is scheduled to fly from
Antarctica in December 2017 for 28 days and will be the first balloon-borne
telescope to offer a quarter of the flight for "shared risk" observing by the
community.Comment: Presented at SPIE Millimeter, Submillimeter, and Far-Infrared
Detectors and Instrumentation for Astronomy VIII, June 29th, 201
CLiC Dickens:novel uses of concordances for the integration of corpus stylistics and cognitive poetics
Voting Technology, Vote-by-Mail, and Residual Votes in California, 1990-2010
This paper examines how the growth in vote-by-mail and changes in voting technologies led to changes in the residual vote rate in California from 1990 to 2010. We find that in California’s presidential elections, counties that abandoned punch cards in favor of optical scanning enjoyed a significant improvement in the residual vote rate. However, these findings do not always translate to other races. For instance, find that the InkaVote system in Los Angeles has been a mixed success, performing very well in presidential and gubernatorial races, fairly well for ballot propositions, and poorly in Senate races. We also conduct the first analysis of the effects of the rise of vote-by-mail on residual votes. Regardless of the race, increased use of the mails to cast ballots is robustly associated with a rise in the residual vote rate. The effect is so strong that the rise of voting by mail in California has mostly wiped out all the reductions in residual votes that were due to improved voting technologies since the early 1990s
The use of LiDCO based fluid management in patients undergoing hip fracture surgery under spinal anaesthesia: Neck of femur optimisation therapy - targeted stroke volume (NOTTS): study protocol for a randomized controlled trial
Exploring a new paradigm for the fetal anomaly ultrasound scan: Artificial intelligence in real time
Objective Advances in artificial intelligence (AI) have demonstrated potential to improve medical diagnosis. We piloted the end-to-end automation of the mid-trimester screening ultrasound scan using AI-enabled tools. Methods A prospective method comparison study was conducted. Participants had both standard and AI-assisted US scans performed. The AI tools automated image acquisition, biometric measurement, and report production. A feedback survey captured the sonographers' perceptions of scanning. Results Twenty-three subjects were studied. The average time saving per scan was 7.62 min (34.7%) with the AI-assisted method (p < 0.0001). There was no difference in reporting time. There were no clinically significant differences in biometric measurements between the two methods. The AI tools saved a satisfactory view in 93% of the cases (four core views only), and 73% for the full 13 views, compared to 98% for both using the manual scan. Survey responses suggest that the AI tools helped sonographers to concentrate on image interpretation by removing disruptive tasks. Conclusion Separating freehand scanning from image capture and measurement resulted in a faster scan and altered workflow. Removing repetitive tasks may allow more attention to be directed identifying fetal malformation. Further work is required to improve the image plane detection algorithm for use in real time
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