2,377 research outputs found
The Airy fibre: an optical fibre that guides light diffracted by a circular aperture
We have designed and made an optical fibre that guides an approximate Airy
pattern as one of its guided modes. The fibre's attenuation was 11.0 dB/km at
1550 nm wavelength, the match between the fibre's mode and the ideal infinite
Airy pattern was 93.7%, and the far field resembled a top-hat beam. The
guidance mechanism has strong similarities to photonic bandgap guidance.Comment: 11 page
Streamlined life cycle assessment of transparent silica aerogel made by supercritical drying
This is the post-print version of the Article. The official published version can be accessed from the link below - Copyright @ 2011 ElsevierWhen developing sustainable building fabric technologies, it is essential that the energy use and CO2 burden arising from manufacture does not outweigh the respective in-use savings. This study investigates this paradigm by carrying out a streamlined life cycle assessment (LCA) of silica aerogel. This unique, nanoporous translucent insulation material has the lowest thermal conductivity of any solid, retaining up to four times as much heat as conventional insulation, whilst being highly transparent to light and solar radiation. Monolithic silica aerogel has been cited as the âholy grailâ of future glazing technology. Alternatively, translucent granular aerogel is now being produced on a commercial scale. In each case, many solvents are used in production, often accompanied by intensive drying processes, which may consume large amounts of energy and CO2. To date, there has been no peer-reviewed LCA of this material conducted to the ISO 14000 standard. Primary data for this âcradle-to-factory gateâ LCA is collected for silica aerogel made by low and high temperature supercritical drying. In both cases, the mass of raw materials and electricity usage for each process is monitored to determine the total energy use and CO2 burden. Findings are compared against the predicted operational savings arising from retrofitting translucent silica aerogel to a single glazed window to upgrade its thermal performance. Results should be treated as a conservative estimate as the aerogel is produced in a laboratory, which has not been developed for mass manufacture or refined to reduce its environmental impact. Furthermore, the samples are small and assumptions to upscale the manufacturing volume occur without major changes to production steps or equipment used. Despite this, parity between the CO2 burden and CO2 savings is achieved in less than 2 years, indicating that silica aerogel can provide a measurable environmental benefit.This work is funded by the EPSRC, Brunel University and Buro Happold Ltd, the University of Bath is funded by the EPSRC grant EP/F018622/1
Perspectives on Just War in Tolkienâs Legendarium
The Ainulindalë shows that in Middle-earth war is not an option: the seeds of harmony and discordance are sown at the outset and between the alpha and the omega, races and individuals will attune to the Great Music or take part in the discordance. Their trajectories highlight the perspectives of their Creator or, from the standpoint of the reader, of their sub-creator.
Owing to the centrality of warfare in the history of Middle-earth, this paper will look into the motivations of the races and people engaged in conflicts, whether they be waged with seemingly justifiable intentions or not, whether they be defensive, preventive or aggressive. In the light of scholarly viewpoints (such as that of Saint Augustine) and judging by the short and long-term outcomes of hostilities in the history of Middle-earth, an attempt will be made to identify perspectives on the concept of âjust warâ in Tolkienâs secondary world.
Romanticism, Symbolism and Onomastics in Tolkienâs Legendarium
E.B. Burgum once wrote in the Kenyon Review (1941): âHe who seeks to define Romanticism is entering a hazardous occupation which has claimed many victimsâ. However there is no denying that sensibility is one of the consensual pointers. And if one seeks to explore Professor Tolkienâs motives behind the unfolding of his Legendarium, there is again no denying that his self-avowed extreme sensitivity to words and languages is not only a pointer but also lies at the root of his entire writing process. Such visceral fascination for the beauty and musicality of words can be found in the etymology and symbolism of personal and place names throughout Middle-earth. As a contribution to the study of romanticism in Tolkienâs works, this paper examines the possible characteristics of this complex movement that find an echo in the authorâs onomastic sub-creation and the latterâs subsequent relation to the characters, places and objects in Middle-earth
The Photonic Lantern
Photonic lanterns are made by adiabatically merging several single-mode cores
into one multimode core. They provide low-loss interfaces between single-mode
and multimode systems where the precise optical mapping between cores and
individual modes is unimportant.Comment: 45 pages; article unchanged, accepted for publication in Advances in
Optics and Photonic
The high-lying Li levels at excitation energy around 21 MeV
The H+He cluster structure in Li was investigated by the
H(,H He)n kinematically complete experiment at the incident
energy = 67.2 MeV. We have observed two resonances at =
21.30 and 21.90 MeV which are consistent with the He(H, )Li
analysis in the Ajzenberg-Selove compilation. Our data are compared with the
previous experimental data and the RGM and CSRGM calculations.Comment: 12 pages, 6 figures. Accepted for publication in J. Phys. Soc. Jp
Segmented scintillation detectors with silicon photomultiplier readout for measuring antiproton annihilations
The Atomic Spectroscopy and Collisions Using Slow Antiprotons (ASACUSA)
experiment at the Antiproton Decelerator (AD) facility of CERN constructed
segmented scintillators to detect and track the charged pions which emerge from
antiproton annihilations in a future superconducting radiofrequency Paul trap
for antiprotons. A system of 541 cast and extruded scintillator bars were
arranged in 11 detector modules which provided a spatial resolution of 17 mm.
Green wavelength-shifting fibers were embedded in the scintillators, and read
out by silicon photomultipliers which had a sensitive area of 1 x 1 mm^2. The
photoelectron yields of various scintillator configurations were measured using
a negative pion beam of momentum p ~ 1 GeV/c. Various fibers and silicon
photomultipliers, fiber end terminations, and couplings between the fibers and
scintillators were compared. The detectors were also tested using the
antiproton beam of the AD. Nonlinear effects due to the saturation of the
silicon photomultiplier were seen at high annihilation rates of the
antiprotons.Comment: Copyright 2014 American Institute of Physics. This article may be
downloaded for personal use only. Any other use requires prior permission of
the author and the American Institute of Physics. The following article
appeared in Review of Scientific Instruments, Vol.85, Issue 2, 2014 and may
be found at http://dx.doi.org/10.1063/1.486364
Low-loss criterion and effective area considerations for photonic crystal fibers
We study the class of endlessly single-mode all-silica photonic crystal
fibers with a triangular air-hole cladding. We consider the sensibility to
longitudinal nonuniformities and the consequences and limitations for realizing
low-loss large-mode area photonic crystal fibers. We also discuss the
dominating scattering mechanism and experimentally we confirm that both macro
and micro-bending can be the limiting factor.Comment: Accepted for Journal of Optics A - Pure and Applied Optic
Magic wavelengths for the np-ns transitions in alkali-metal atoms
Extensive calculations of the electric-dipole matrix elements in alkali-metal
atoms are conducted using the relativistic all-order method. This approach is a
linearized version of the coupled-cluster method, which sums infinite sets of
many-body perturbation theory terms. All allowed transitions between the lowest
ns, np_1/2, np_3/2 states and a large number of excited states are considered
in these calculations and their accuracy is evaluated. The resulting
electric-dipole matrix elements are used for the high-precision calculation of
frequency-dependent polarizabilities of the excited states of alkali-metal
atoms. We find magic wavelengths in alkali-metal atoms for which the ns and
np_1/2 and np_3/2 atomic levels have the same ac Stark shifts, which
facilitates state-insensitive optical cooling and trapping.Comment: 12 pages, 8 figure
The radical character of the acenes: A density matrix renormalization group study
We present a detailed investigation of the acene series using high-level
wavefunction theory. Our ab-initio Density Matrix Renormalization Group
algorithm has enabled us to carry out Complete Active Space calculations on the
acenes from napthalene to dodecacene correlating the full pi-valence space.
While we find that the ground-state is a singlet for all chain-lengths,
examination of several measures of radical character, including the natural
orbitals, effective number of unpaired electrons, and various correlation
functions, suggests that the longer acene ground-states are polyradical in
nature.Comment: 10 pages, 8 figures, supplementary material, to be published in J.
Chem. Phys. 127, 200
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