12,023 research outputs found
On-Body Channel Measurement Using Wireless Sensors
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Longitudinal excitations in quantum antiferromagnets
By extending our recently proposed magnon-density-waves to low dimensions, we
investigate, using a microscopic many-body approach, the longitudinal
excitations of the quasi-one-dimensional (quasi-1d) and quasi-2d Heisenberg
antiferromagnetic systems on a bipartite lattice with a general spin quantum
number. We obtain the full energy spectrum of the longitudinal mode as a
function of the coupling constants in the original lattice Hamiltonian and find
that it always has a non-zero energy gap if the ground state has a long-range
order and becomes gapless for the pure isotropic 1d model. The numerical value
of the minimum gap in our approximation agrees with that of a longitudinal mode
observed in the quasi-1d antiferromagnetic compound KCuF at low
temperature. It will be interesting to compare values of the energy spectrum at
other momenta if their experimental results are available.Comment: 19 pages, 4 figure
On the Gromov-Witten invariants of the moduli of bundles on a surface.
Depto. de Álgebra, Geometría y TopologíaFac. de Ciencias MatemáticasTRUEpu
Interoperability specification development for integrated BIM use in performance based design
Interoperability in BIM is low and the focus is on 3D coordination. Despite the available standards including IFC and IDM, there is still no clear guidance how such standards can be effectively used for performance based design. Thus, early collaboration is discouraged and performance analysis is conducted as late as possible to minimize the number of information exchanges, leading to difficulties and costly changes in design that is almost completed.
The aim is to propose an interoperability specification development approach for performance based design through the Design4Energy case study project. Findings show that the design process had increased flexibility, shared understanding between stakeholders about what information nuggets should be provided from whom to whom, at what stage, using which tool and data model.
It can guide for the integrated BIM practice and help developing BIM execution plans for Level 2 BIM while paving the way for Level 3 BIM
Photo-desorption of H2O:CO:NH3 circumstellar ice analogs: Gas-phase enrichment
We study the photo-desorption occurring in HO:CO:NH ice mixtures
irradiated with monochromatic (550 and 900 eV) and broad band (250--1250 eV)
soft X-rays generated at the National Synchrotron Radiation Research Center
(Hsinchu, Taiwan). We detect many masses photo-desorbing, from atomic hydrogen
(m/z = 1) to complex species with m/z = 69 (e.g., CHNO, CHO,
CHN), supporting the enrichment of the gas phase.
At low number of absorbed photons, substrate-mediated exciton-promoted
desorption dominates the photo-desorption yield inducing the release of weakly
bound (to the surface of the ice) species; as the number of weakly bound
species declines, the photo-desorption yield decrease about one order of
magnitude, until porosity effects, reducing the surface/volume ratio, produce a
further drop of the yield.
We derive an upper limit to the CO photo-desorption yield, that in our
experiments varies from 1.4 to 0.007 molecule photon in the range ~absorbed photons cm. We apply these findings to a
protoplanetary disk model irradiated by a central T~Tauri star
Accretion and photodesorption of CO ice as a function of the incident angle of deposition
Non-thermal desorption of inter- and circum-stellar ice mantles on dust
grains, in particular ultraviolet photon-induced desorption, has gained
importance in recent years. These processes may account for the observed gas
phase abundances of molecules like CO toward cold interstellar clouds. Ice
mantle growth results from gas molecules impinging on the dust from all
directions and incidence angles. Nevertheless, the effect of the incident angle
for deposition on ice photo-desorption rate has not been studied. This work
explores the impact on the accretion and photodesorption rates of the incidence
angle of CO gas molecules with the cold surface during deposition of a CO ice
layer. Infrared spectroscopy monitored CO ice upon deposition at different
angles, ultraviolet-irradiation, and subsequent warm-up. Vacuum-ultraviolet
spectroscopy and a Ni-mesh measured the emission of the ultraviolet lamp.
Molecules ejected from the ice to the gas during irradiation or warm-up were
characterized by a quadrupole mass spectrometer. The photodesorption rate of CO
ice deposited at 11 K and different incident angles was rather stable between 0
and 45. A maximum in the CO photodesorption rate appeared around
70-incidence deposition angle. The same deposition angle leads to the
maximum surface area of water ice. Although this study of the surface area
could not be performed for CO ice, the similar angle dependence in the
photodesorption and the ice surface area suggests that they are closely
related. Further evidence for a dependence of CO ice morphology on deposition
angle is provided by thermal desorption of CO ice experiments
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