7,006 research outputs found
Investigation of HNCO isomers formation in ice mantles by UV and thermal processing: an experimental approach
Current gas phase models do not account for the abundances of HNCO isomers
detected in various environments, suggesting a formation in icy grain mantles.
We attempted to study a formation channel of HNCO and its possible isomers by
vacuum-UV photoprocessing of interstellar ice analogues containing HO,
NH, CO, HCN, CHOH, CH, and N followed by warm-up, under
astrophysically relevant conditions. Only the HO:NH:CO and HO:HCN
ice mixtures led to the production of HNCO species. The possible isomerization
of HNCO to its higher energy tautomers following irradiation or due to ice
warm-up has been scrutinized. The photochemistry and thermal chemistry of
HO:NH:CO and HO:HCN ices was simulated using the Interstellar
Astrochemistry Chamber (ISAC), a state-of-the-art ultra-high-vacuum setup. The
ice was monitored in situ by Fourier transform mid-infrared spectroscopy in
transmittance. A quadrupole mass spectrometer (QMS) detected the desorption of
the molecules in the gas phase. UV-photoprocessing of
HO:NH:CO/HO:HCN ices lead to the formation of OCN as main
product in the solid state and a minor amount of HNCO. The second isomer HOCN
has been tentatively identified. Despite its low efficiency, the formation of
HNCO and the HOCN isomers by UV-photoprocessing of realistic simulated ice
mantles, might explain the observed abundances of these species in PDRs, hot
cores, and dark clouds
A prototype reactor to compost agricultural wastes of Fusagasuga Municipality. Colombia
Crop and animal production generate a high level of organic waste that causes negative
effects on the environment and communities. The use of composting processes can improve the
quality of these biowastes. Additionally, the application of technologies such as telemetry and
remote sensors, allows optimizing the transformation of organic matter in a more controlled and
efficient way. The city of Fusagasugá is well known in agriculture. However, it lacks sustainable
management of the organic waste system.
In this study, after a three-dimensional electromechanical design, a prototype reactor to compost
agricultural wastes of Fusagasuga municipality will provide. The capacity of this prototype
reactor is considered to be 20 litres. In order to control temperature and humidity of biowastes in
different working conditions, it is used A PI controller with 3 temperature and a humidity sensors.
With these sensors the compost materials temperature and humidity will remain at 65 °C and
55–60%. By using a special form of temperature sensor placement, the time to oxygenate the
compost materials will be found. Furthermore, this system is integrated by a Human-Machine
Interface (HMI), which allows the supervision and manipulation from a remote access user
Runaway evaporation for optically dressed atoms
Forced evaporative cooling in a far-off-resonance optical dipole trap is
proved to be an efficient method to produce fermionic- or bosonic-degenerated
gases. However in most of the experiences, the reduction of the potential
height occurs with a diminution of the collision elastic rate. Taking advantage
of a long-living excited state, like in two-electron atoms, I propose a new
scheme, based on an optical knife, where the forced evaporation can be driven
independently of the trap confinement. In this context, the runaway regime
might be achieved leading to a substantial improvement of the cooling
efficiency. The comparison with the different methods for forced evaporation is
discussed in the presence or not of three-body recombination losses
Degenerate Fermi Gas of Sr
We report quantum degeneracy in a gas of ultra-cold fermionic Sr
atoms. By evaporatively cooling a mixture of spin states in an optical dipole
trap for 10.5\,s, we obtain samples well into the degenerate regime with
. The main signature of degeneracy is a change in the
momentum distribution as measured by time-of-flight imaging, and we also
observe a decrease in evaporation efficiency below .Comment: 4 pages, 3 figure
Inelastic and elastic collision rates for triplet states of ultracold strontium
We report measurement of the inelastic and elastic collision rates for
^{88}Sr atoms in the (5s5p)^3P_0 state in a crossed-beam optical dipole trap.
This is the first measurement of ultracold collision properties of a ^3P_0
level in an alkaline-earth atom or atom with similar electronic structure.
Since the (5s5p)^3P_0 state is the lowest level of the triplet manifold, large
loss rates indicate the importance of principle-quantum-number-changing
collisions at short range. We also provide an estimate of the collisional loss
rates for the (5s5p){^3P_2} state.Comment: 4 pages 5 figure
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
- …