1,055 research outputs found
Densities and phase equilibria of hydrogen, propane and vegetable oil mixtures. Experimental data and thermodynamic modeling
Heterogeneous catalytic gas-liquid reactions are intensified when carried out in the homogenous fluid phase by means of a supercritical co-solvent. For instance, supercritical propane is used to enhance yield in the hydrogenation of vegetable oils. Besides phase equilibrium knowledge, volumetric information is also needed to elucidate kinetic mechanisms and design continuous supercritical reactors. In this work, we report new experimental PvT data of the reactive mixture H2+sunflower oil+propane using the isochoric method. In addition, the phase equilibria and PvT data are modeled with the GCA and RK-PR equations of state, respectively. The isochoric method not only provides PvT information under the reaction conditions, but also the reactive system compressibility, key variable to attain enhanced transport properties in the supercritical reactors.Fil: Hegel, Pablo Ezequiel. Consejo Nacional de Investigaciones CientĂficas y TĂŠcnicas. Centro CientĂfico TecnolĂłgico Conicet - BahĂa Blanca. Planta Piloto de IngenierĂa QuĂmica. Universidad Nacional del Sur. Planta Piloto de IngenierĂa QuĂmica; ArgentinaFil: Cotabarren, Natalia Soledad. Consejo Nacional de Investigaciones CientĂficas y TĂŠcnicas. Centro CientĂfico TecnolĂłgico Conicet - BahĂa Blanca. Planta Piloto de IngenierĂa QuĂmica. Universidad Nacional del Sur. Planta Piloto de IngenierĂa QuĂmica; ArgentinaFil: Brignole, Esteban Alberto. Consejo Nacional de Investigaciones CientĂficas y TĂŠcnicas. Centro CientĂfico TecnolĂłgico Conicet - BahĂa Blanca. Planta Piloto de IngenierĂa QuĂmica. Universidad Nacional del Sur. Planta Piloto de IngenierĂa QuĂmica; ArgentinaFil: Pereda, Selva. Consejo Nacional de Investigaciones CientĂficas y TĂŠcnicas. Centro CientĂfico TecnolĂłgico Conicet - BahĂa Blanca. Planta Piloto de IngenierĂa QuĂmica. Universidad Nacional del Sur. Planta Piloto de IngenierĂa QuĂmica; Argentina. University of KwaZulu-Natal; SudĂĄfric
APOLLO: the Apache Point Observatory Lunar Laser-ranging Operation: Instrument Description and First Detections
A next-generation lunar laser ranging apparatus using the 3.5 m telescope at
the Apache Point Observatory in southern New Mexico has begun science
operation. APOLLO (the Apache Point Observatory Lunar Laser-ranging Operation)
has achieved one-millimeter range precision to the moon which should lead to
approximately one-order-of-magnitude improvements in the precision of several
tests of fundamental properties of gravity. We briefly motivate the scientific
goals, and then give a detailed discussion of the APOLLO instrumentation.Comment: 37 pages; 10 figures; 1 table: accepted for publication in PAS
WISE J072003.20-084651.2: An Old and Active M9.5 + T5 Spectral Binary 6 pc from the Sun
[Abridged] We report observations of the recently discovered, nearby late-M
dwarf WISE J072003.20-084651.2. Astrometric measurements obtained with TRAPPIST
improve the distance measurement to 6.01.0 pc and confirm the low
tangential velocity (3.50.6 km/s) reported by Scholz. Low-resolution
optical spectroscopy indicates a spectral type of M9.5 and prominent H
emission ( = -4.680.06), but no evidence of subsolar
metallicity or Li I absorption. Near-infrared spectroscopy reveals subtle
peculiarities indicating the presence of a T5 binary companion, and
high-resolution laser guide star adaptive optics imaging reveals a faint
(H = 4.1) candidate source 0"14 (0.8 AU) from the primary. We measure a
stable radial velocity of +83.80.3 km/s, indicative of old disk kinematics
and consistent with the angular separation of the possible companion. We
measure a projected rotational velocity of v sin i = 8.00.5 km/s, and find
evidence of low-level variability (~1.5%) in a 13-day TRAPPIST lightcurve, but
cannot robustly constrain the rotational period. We also observe episodic
changes in brightness (1-2%) and occasional flare bursts (4-8%) with a 0.8%
duty cycle, and order-of-magnitude variations in H line strength.
Combined, these observations reveal WISE J0720-0846 to be an old, very low-mass
binary whose components straddle the hydrogen burning minimum mass, and whose
primary is a relatively rapid rotator and magnetically active. It is one of
only two known binaries among late M dwarfs within 10 pc of the Sun, both
harboring a mid T-type brown dwarf companion. While this specific configuration
is rare (1.4% probability), roughly 25% of binary companions to late-type M
dwarfs in the local population are likely low-temperature T or Y brown dwarfs.Comment: 18 pages, 23 figures; accepted for publication in A
Real-Gas Effects and Phase Separation in Underexpanded Jets at Engine-Relevant Conditions
A numerical framework implemented in the open-source tool OpenFOAM is
presented in this work combining a hybrid, pressure-based solver with a
vapor-liquid equilibrium model based on the cubic equation of state. This
framework is used in the present work to investigate underexpanded jets at
engine-relevant conditions where real-gas effects and mixture induced phase
separation are probable to occur. A thorough validation and discussion of the
applied vapor-liquid equilibrium model is conducted by means of general
thermodynamic relations and measurement data available in the literature.
Engine-relevant simulation cases for two different fuels were defined. Analyses
of the flow field show that the used fuel has a first order effect on the
occurrence of phase separation. In the case of phase separation two different
effects could be revealed causing the single-phase instability, namely the
strong expansion and the mixing of the fuel with the chamber gas. A comparison
of single-phase and two-phase jets disclosed that the phase separation leads to
a completely different penetration depth in contrast to single-phase injection
and therefore commonly used analytical approaches fail to predict the
penetration depth.Comment: Preprint submitted to AIAA Scitech 2018, Kissimmee, Florid
Airfoil data sensitivity analysis for actuator disc simulations used in wind turbine applications
To analyse the sensitivity of blade geometry and airfoil characteristics on the prediction of performance characteristics of wind farms, large-eddy simulations using an actuator disc (ACD) method are performed for three different blade/airfoil configurations. The aim of the study is to determine how the mean characteristics of wake flow, mean power production and thrust depend on the choice of airfoil data and blade geometry. In order to simulate realistic conditions, pre-generated turbulence and wind shear are imposed in the computational domain. Using three different turbulence intensities and varying the spacing between the turbines, the flow around 4-8 aligned turbines is simulated. The analysis is based on normalized mean streamwise velocity, turbulence intensity, relative mean power production and thrust. From the computations it can be concluded that the actual airfoil characteristics and blade geometry only are of importance at very low inflow turbulence. At realistic turbulence conditions for an atmospheric boundary layer the specific blade characteristics play an minor role on power performance and the resulting wake characteristics. The results therefore give a hint that the choice of airfoil data in ACD simulations is not crucial if the intention of the simulations is to compute mean wake characteristics using a turbulent inflow
Optical properties of an effective one-band Hubbard model for the cuprates
We study the Cu and O spectral density of states and the optical conductivity
of CuO_2 planes using an effective generalized one-band Hubbard model derived
from the extended three-band Hubbard model. We solve exactly a square cluster
of 10 unit cells and average the results over all possible boundary conditions,
what leads to smooth functions of frequency. Upon doping, the Fermi energy
jumps to Zhang-Rice states which are connected to the rest of the valence band
(in contrast to an isolated new band in the middle of the gap). The transfer of
spectral weight depends on the parameters of the original three-band model not
only through the one-band effective parameters but also through the relevant
matrix elements. We discuss the evolution of the gap upon doping. The optical
conductivity of the doped system shows a mid-infrared peak due to intraband
transitions, a pseudogap and a high frequency part related to interband
transitions. Its shape and integrated weight up to a given frequency (including
the Drude weight) agree qualitatively with experiments in the cuprates for low
to moderate doping levels, but significant deviations exist for doping .Comment: 11 pages (tex), 14 figures (ps
GPsâ strategies in exploring the preschool childâs wellbeing in the paediatric consultation
Background:
Although General Practitioners (GPs) are uniquely placed to identify children with emotional, social, and behavioural problems, they succeed in identifying only a small number of them. The aim of this article is to explore the strategies, methods, and tools employed by GPs in the assessment of the preschool childâs emotional, mental, social, and behavioural health. We look at how GPs address parental care of the child in general and in situations where GPs have a particular awareness of the child.
Method:
Twenty-eight Danish GPs were purposively selected to take part in a qualitative study which combined focus-group discussions, observation of child consultations, and individual interviews with GPs.
Results:
Analysis of the data suggests that GPs have developed a set of methods, and strategies to assess the preschool child and parental care of the child. They look beyond paying narrow attention to the physical health of the child and they have expanded their practice to include the relations and interactions in the consultation room. The physical examination of the child continues to play a central role in doctor-child communication.
Conclusion:
The participating GPsâ strategies helped them to assess the wellbeing of the preschool child but they often find it difficult to share their impressions with parents
- âŚ