8,165 research outputs found
Improving the tensile strength of carbon nanotube spun yarns using a modified spinning process
A modified process for the dry spinning of carbon nanotube (CNT) yarn is reported. The approach gives an improved structure of CNT bundles in the web drawn from the CNT forest and in the yarn produced from the twisted web leading to improved mechanical properties of the yarn. The process enables many different mechanical and physical treatments to be applied to the individual stages of the pure CNT spinning system, and may allow potential for the development of complex spinning processes such as polymer–CNT-based composite yarns. The tensile strength and yarn/web structure of yarn spun using this approach have been investigated and evaluated using standard tensile testing methods along with scanning electron microscopy. The experimental results show that the tensile properties were significantly improved. The effect of heat treatments and other yarn constructions on the tensile properties are also reported
The Milky Way bar/bulge in proper motions: a 3D view from VIRAC & Gaia
© 2019 The Author(s) Published by Oxford University Press on behalf of the Royal Astronomical Society.We have derived absolute proper motions of the entire Galactic bulge region from VIRAC and Gaia. We present these as both integrated on-sky maps and, after isolating standard candle red clump (RC) stars, as a function of distance using RC magnitude as a proxy. These data provide a new global, 3-dimensional view of the Milky Way barred bulge kinematics. We find a gradient in the mean longitudinal proper motion, , between the different sides of the bar, which is sensitive to the bar pattern speed. The split RC has distinct proper motions and is colder than other stars at similar distance. The proper motion correlation map has a quadrupole pattern in all magnitude slices showing no evidence for a separate, more axisymmetric inner bulge component. The line-of-sight integrated kinematic maps show a high central velocity dispersion surrounded by a more asymmetric dispersion profile. is smallest, , near the minor axis and reaches near the disc plane. The integrated pattern signals a superposition of bar rotation and internal streaming motion, with the near part shrinking in latitude and the far part expanding. To understand and interpret these remarkable data, we compare to a made-to-measure barred dynamical model, folding in the VIRAC selection function to construct mock maps. We find that our model of the barred bulge, with a pattern speed of 37.5 , is able to reproduce all observed features impressively well. Dynamical models like this will be key to unlocking the full potential of these data.Peer reviewe
The circumstellar environment of the YSO TMR-1 and a revisit to the candidate very low-mass object TMR-1C
TMR-1 (IRAS~04361+2547) is a class~I proto-stellar source located in the
nearby Taurus star-forming region. Its circumstellar environment is
characterized by extended dust emission with complex structures and conspicuous
filaments. A faint companion, called TMR-1C, located near the proto-star had
been detected in previous studies, but its nature as a very young substellar
object remained inconclusive. To improve the constraints on the nature of
TMR-1C, and to investigate the process of very low-mass star formation in the
TMR-1 system we use very sensitive infrared imaging observations as well as NIR
spectroscopy. We construct the SED of TMR-1C over a much larger wavelength
range as had been possible in previous work and compare it with models of
extincted background stars, young sub-stellar objects, and very low-mass stars
with circumstellar disk and envelope emission. We also search for additional
low-luminosity objects in the immediate environment of the TMR-1, study the
surrounding NIR dust morphology, and analyse the emission line spectrum of a
filamentary structure in the physical context of a bow-shock model. We find
that the observed SED of TMR-1C is inconsistent with an extincted background
star, nor can be fitted with available models for a young extremely low-mass
(<12M_Jup) object. Our near-IR spectrum indicates an effective temperature of
at least ~3000K. Based on a good match of TMR-1C's SED with radiation transfer
models of young stellar objects with circumstellar disks, we propose that
TMR-1C is most likely a very low-mass star with M~0.1-0.2M_sun surrounded by a
circumstellar disk with high inclination, i>80deg. Moreover, we detect an
additional very faint source, which we call TMR-1D, and that shows a quite
striking symmetry in position with TMR-1C. TMR-1C and TMR-1D may have been
formed from a common triggered star-formation event, caused by... (abstract
abridged)Comment: 15 pages, 11 figures, accepted for publication in A&
Methods to prioritise pop-up active transport infrastructure and their application in a national cycleway prioritisation tool
In the context of reduced public transport capacity in the wake of the COVID-19 pandemic, governments are scrambling to enable walking and cycling while adhering to physical distancing guidelines. Many pop-up options exist. Of these, road space reallocation represents a ‘quick win’ for cities with ‘spare space’ along continuous road sections that have high latent cycling potential. We developed methods to condense the complexity of city networks down to the most promising roads for road space reallocation schemes. The resulting Rapid Cycleway Prioritisation Tool has been deployed for all cities in England to help prioritise emergency funds for new cycleways nationwide. The methods and concepts could be used to support investment in pop-up infrastructure in cities worldwide
Dryland pasture yields and botanical composition over 5 years under sheep grazing in Canterbury
Annual dry matter (DM) production and botanical
composition of six dryland pasture combinations, grown
under sheep grazing at Lincoln University for 5 years,
are presented. In 4 years, lucerne produced the highest
DM yields (13.1-18.5 t/ha/yr) through higher daily
growth rates, compared with grass based pastures,
particularly during periods of water stress in summer
and autumn. Of the grass based pastures, cocksfoot sown
with subterranean clover produced yields of 9.9-12.9 t
DM/ha/yr which were greater than, or similar to, all other
pastures (8.0-12.9 t DM/ha/yr). Cocksfoot established
with white clover produced >9.7 t DM/ha/yr in years
with wetter than average summers. Over the 5 years the
contribution of perennial ryegrass to total DM yield
declined by ~0.7 t/ha/yr, from 70% in Year 1, to 44% in
Year 5. It was replaced by unsown dicotyledonous weeds
and grasses which increased from 4% in Year 1 to 24%
by Year 5. Overall results show a dryland pastoral system
that includes both lucerne and cocksfoot with subterranean
clover pastures is likely to produce more feed in dry
years than perennial ryegrass/white clover pastures. The
inclusion of white clover with cocksfoot and subterranean
clover may allow utilisation of variable and unpredictable
rainfall in moist summers.A. Mills acknowledges financial assistance from Meat
& Wool NZ through the FoRST Pastoral21 programme,
Lincoln University and the Cocksfoot Growers
Association
Room-temperature exciton-polaritons with two-dimensional WS2
Two-dimensional transition metal dichalcogenides exhibit strong optical
transitions with significant potential for optoelectronic devices. In
particular they are suited for cavity quantum electrodynamics in which strong
coupling leads to polariton formation as a root to realisation of inversionless
lasing, polariton condensationand superfluidity. Demonstrations of such
strongly correlated phenomena to date have often relied on cryogenic
temperatures, high excitation densities and were frequently impaired by strong
material disorder. At room-temperature, experiments approaching the strong
coupling regime with transition metal dichalcogenides have been reported, but
well resolved exciton-polaritons have yet to be achieved. Here we report a
study of monolayer WS coupled to an open Fabry-Perot cavity at
room-temperature, in which polariton eigenstates are unambiguously displayed.
In-situ tunability of the cavity length results in a maximal Rabi splitting of
meV, exceeding the exciton linewidth. Our data
are well described by a transfer matrix model appropriate for the large
linewidth regime. This work provides a platform towards observing strongly
correlated polariton phenomena in compact photonic devices for ambient
temperature applications.Comment: 12 pages, 6 figure
Focusing of quantum gate interactions using dynamical decoupling
In 1995, Cirac and Zoller proposed the first concrete implementation of a
small-scale quantum computer, using laser beams focused to micron spot sizes to
address individual trapped ions in a linear crystal. Here we propose a method
to focus entangling gate interactions, but driven by microwave fields, to
micron-sized zones, corresponding to microwave wavelengths. We
demonstrate the ability to suppress the spin-dependent force using a single
ion, and find the required interaction introduces error
per emulated gate in a single-qubit benchmarking sequence. We model the scheme
for a 17-qubit ion crystal, and find that any pair of ions should be
addressable with an average crosstalk error of
Testing General Relativity with Current Cosmological Data
Deviations from general relativity, such as could be responsible for the
cosmic acceleration, would influence the growth of large scale structure and
the deflection of light by that structure. We clarify the relations between
several different model independent approaches to deviations from general
relativity appearing in the literature, devising a translation table. We
examine current constraints on such deviations, using weak gravitational
lensing data of the CFHTLS and COSMOS surveys, cosmic microwave background
radiation data of WMAP5, and supernova distance data of Union2. Markov Chain
Monte Carlo likelihood analysis of the parameters over various redshift ranges
yields consistency with general relativity at the 95% confidence level.Comment: 11 pages; 7 figures; typographical errors corrected; this is the
published versio
Strong exciton-photon coupling with colloidal nanoplatelets in an open microcavity
Colloidal semiconductor nanoplatelets exhibit quantum size effects due to
their thickness of only few monolayers, together with strong optical band-edge
transitions facilitated by large lateral extensions. In this article we
demonstrate room temperature strong coupling of the light and heavy hole
exciton transitions of CdSe nanoplatelets with the photonic modes of an open
planar microcavity. Vacuum Rabi splittings of meV and meV
are observed for the heavy and light hole excitons respectively, together with
a polariton-mediated hybridisation of both transitions. By measuring the
concentration of platelets in the film we compute the transition dipole moment
of a nanoplatelet exciton to be D. The large oscillator
strength and fluorescence quantum yield of semiconductor nanoplatelets provide
a perspective towards novel photonic devices, combining polaritonic and
spinoptronic effects.Comment: 9 pages, 4 figure
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