6,525 research outputs found
Mobile onsite exploration of parallel realities with Oculus Rift
This paper reports experience in developing a parallel reality system which allows its user to observe and move around their real environment whilst wearing a stereoscopic 3D head mounted display imbued with video-see through capabilities, with their position and gaze tracked by an indoor positioning system and head tracker, allowing them to alternately view their real environment and an immersive virtual reality environment from the equivalent vantage point. In so doing the challenge of the vacancy problem is addressed by lightening the cognitive load needed to switch between realities and to navigate the virtual environment. Evaluation of the usability, system performance and value of the system are undertaken in the context of a cultural heritage application; users are able to compare a reconstruction of an important 15th century chapel with its present day instantiation.Postprin
Highly-functionalised difluorinated cyclohexane polyols via the DielsâAlder reaction : regiochemical control via the phenylsulfonyl group
A difluorinated dienophile underwent cycloaddition reactions with a range of furans to afford cycloadducts whichcould be processed regio- and stereoselectively via episulfonium ions, generated by the reaction between their alkenyl groups and phenylsulfenyl chloride. The oxabicyclic products were oxidised to the phenylsulfonyl level and ring opened via E1CB or reductive desulfonative pathways to afford, ultimately, difluorinated cyclohexene or cyclohexane polyols
Anisotropic random resistor networks: a model for piezoresistive response of thick-film resistors
A number of evidences suggests that thick-film resistors are close to a
metal-insulator transition and that tunneling processes between metallic grains
are the main source of resistance. We consider as a minimal model for
description of transport properties in thick-film resistors a percolative
resistor network, with conducting elements governed by tunneling. For both
oriented and randomly oriented networks, we show that the piezoresistive
response to an applied strain is model dependent when the system is far away
from the percolation thresold, while in the critical region it acquires
universal properties. In particular close to the metal-insulator transition,
the piezoresistive anisotropy show a power law behavior. Within this region,
there exists a simple and universal relation between the conductance and the
piezoresistive anisotropy, which could be experimentally tested by common
cantilever bar measurements of thick-film resistors.Comment: 7 pages, 2 eps figure
The Fe XXII I(11.92 A)/I(11.77 A) Density Diagnostic Applied to the Chandra High Energy Transmission Grating Spectrum of EX Hydrae
Using the Livermore X-ray Spectral Synthesizer, which calculates spectral
models of highly charged ions based primarily on HULLAC atomic data, we
investigate the temperature, density, and photoexcitation dependence of the
I(11.92 A)/I(11.77 A) line ratio of Fe XXII. We find that this line ratio has a
critical density n_c \approx 5x10^13 cm^-3, is approximately 0.3 at low
densities and 1.5 at high densities, and is very insensitive to temperature and
photoexcitation, so is a useful density diagnostic for sources like magnetic
cataclysmic variables in which the plasma densities are high and the efficacy
of the He-like ion density diagnostic is compromised by the presence of a
bright ultraviolet continuum. Applying this diagnostic to the Chandra High
Energy Transmission Grating spectrum of the intermediate polar EX Hya, we find
that the electron density of its T_e \approx 12 MK plasma is n_e =
1.0^{+2.0}_{-0.5} x 10^14 cm^-3, orders of magnitude greater than that
typically observed in the Sun or other late-type stars.Comment: 11 pages including 3 encapsulated postscript figures; LaTeX format,
uses aastex.cls; accepted on 2003 April 3 for publication in The
Astrophysical Journa
Fluctuation-induced first-order phase transition in Dzyaloshinskii-Moriya helimagnets
Two centuries of research on phase transitions have repeatedly highlighted
the importance of critical fluctuations that abound in the vicinity of a
critical point. They are at the origin of scaling laws obeyed by thermodynamic
observables close to second-order phase transitions resulting in the concept of
universality classes, that is of paramount importance for the study of
organizational principles of matter. Strikingly, in case such soft fluctuations
are too abundant they may alter the nature of the phase transition profoundly;
the system might evade the critical state altogether by undergoing a
discontinuous first-order transition into the ordered phase.
Fluctuation-induced first-order transitions have been discussed broadly and are
germane for superconductors, liquid crystals, or phase transitions in the early
universe, but clear experimental confirmations remain scarce. Our results from
neutron scattering and thermodynamics on the model Dzyaloshinskii-Moriya (DM)
helimagnet (HM) MnSi show that such a fluctuation-induced first-order
transition is realized between its paramagnetic and HM state with remarkable
agreement between experiment and a theory put forward by Brazovskii. While our
study clarifies the nature of the HM phase transition in MnSi that has puzzled
scientists for several decades, more importantly, our conclusions entirely
based on symmetry arguments are also relevant for other DM-HMs with only weak
cubic magnetic anisotropies. This is in particular noteworthy in light of a
wide range of recent discoveries that show that DM helimagnetism is at the
heart of problems such as topological magnetic order, multiferroics, and
spintronics.Comment: 19 pages, 9 figures, 2 table
Uso de modelos de simulação sócio-bio-econÎmico integrado como ferramenta para o desenvolvimento agrårio na região sudoeste do Rio Grande Sul.
Suporte tecnolĂłgico tem sido oferecido aos produtores com a finalidade de aumentar a eficiĂȘncia produtiva e fornecer subsĂdios para as suas tomadas de decisĂ”es; entretanto, os mĂ©todos tradicionais de pesquisa e extensĂŁo estĂŁo sendo cada vez mais questionados, principalmente quanto ao custo e tempo necessĂĄrio para oferecer soluçÔes aos problemas enfrentados pelos produtores.bitstream/item/109814/1/USO-DE-MODELOS-DE-SIMULACAO.pd
Atomic data from the IRON Project. I. Electron-impact scattering of Fe17+ using <I>R</I>-matrix theory with intermediate coupling
We present results for electron-impact excitation of F-like Fe calculated using R-matrix theory where an intermediate-coupling frame transformation (ICFT) is used to obtain level-resolved collision strengths. Two such calculations are performed, the first expands the target using 2s2 2p5, 2s 2p6, 2s2 2p4 3l, 2s 2p5 3l, and 2p6 3l configurations while the second calculation includes the 2s2 2p4 4l, 2s 2p5 4l, and 2p6 4l configurations as well. The effect of the additional structure in the latter calculation on the n=3 resonances is explored and compared with previous calculations. We find strong resonant enhancement of the effective collision strengths to the 2s2 2p4 3s levels. A comparison with a Chandra X-ray observation of Capella shows that the n=4 R-matrix calculation leads to good agreement with observation</p
Magnetic phase diagram and transport properties of FeGe_2
We have used resistivity measurements to study the magnetic phase diagram of
the itinerant antiferromagnet FeGe_2 in the temperature range from 0.3->300 K
in magnetic fields up to 16 T. In contrast to theoretical predictions, the
incommensurate spin density wave phase is found to be stable at least up to 16
T, with an estimated critical field \mu _0H_c of ~ 30 T. We have also studied
the low temperature magnetoresistance in the [100], [110], and [001]
directions. The transverse magnetoresistance is well described by a power law
for magnetic fields above 1 T with no saturation observed at high fields. We
discuss our results in terms of the magnetic structure and the calculated
electronic bandstructure of FeGe_2. We have also observed, for the first time
in this compound, Shubnikov-de Haas oscillations in the transverse
magnetoresistance with a frequency of 190 +- 10 T for a magnetic field along
[001].Comment: 13 pages, RevTeX, 7 postscript figures, to appear in Journal of
Physics: Condensed Matte
Policy Insights From the EMF 32 Study on U.S. Carbon Tax Scenarios
The Stanford Energy Modeling Forum exercise 32 (EMF 32) used 11 different models to assess emissions, energy, and economic outcomes from a plausible range of economy-wide carbon price policies to reduce carbon dioxide (CO2) emissions in the United States. Here we discuss the most policy-relevant results of the study, mindful of the strengths and weaknesses of current models. Across all models, carbon prices lead to significant reduc- tions in CO2 emissions and conventional pollutants, with the vast majority of the reductions occurring in the electricity sector. Importantly, emissions reductions do not significantly depend on the rebate or tax cut used to return revenues to the economy. Expected economic costs, as modeled by either GDP or welfare, are modest, but vary across models. These costs are offset by benefits from avoided climate damages and health benefits from reductions in conventional air pollution. Using revenues to reduce preexisting capital or labor taxes reduces costs in most models relative to lump-sum rebates, but the size of the cost reductions varies significantly. Devoting at least some revenue to household rebates can significantly reduce adverse impacts on low income households. Carbon prices at $25/ton or even lower levels cause significant shifts away from coal as an energy source with responses of other energy sources highly dependent upon technology cost assumptions. Beyond 2030, we conclude that model uncertainties are too large to make quantitative results useful for near-term policy design. We close by describing recommendations for policymakers on interacting with model results in the future
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