6,194 research outputs found
Identification of fullerene-like CdSe nanoparticles from optical spectroscopy calculations
Semiconducting nanoparticles are the building blocks of optical nanodevices
as their electronic states, and therefore light absorption and emission, can be
controlled by modifying their size and shape. CdSe is perhaps the most studied
of these nanoparticles, due to the efficiency of its synthesis, the high
quality of the resulting samples, and the fact that the optical gap is in the
visible range. In this article, we study light absorption of CdSe
nanostructures with sizes up to 1.5 nm within density functional theory. We
study both bulk fragments with wurtzite symmetry and novel fullerene-like
core-cage structures. The comparison with recent experimental optical spectra
allows us to confirm the synthesis of these fullerene-like CdSe clusters
Application of Phase Change Materials to Domestic Refrigerators
The paper investigates the performance improvement provided by a phase change material associated with the evaporator in a domestic refrigerator. The heat release and storage rate of encapsulated ice, used as the thermal energy storage material, has been investigated numerically. The mathematical model for phase change is based on the enthalpy method and the governing equations were discretized on a fixed grid using the finite difference method.
The influence of PCM thickness (2, 3 and 4 × 10-3 m slabs), ambient temperature (20°C, 25°C, 30°C and 43°C) and evaporating temperature (-15°C and -10°C) have been investigated. The results showed that the melting and freezing time increased proportionally with PCM thickness. The refrigerator autonomy was reduced by 47% when the ambient temperature was increased from 20°C to 43°C and the freezing time increased by 27% when the evaporating temperature was reduced from -10°C to -15°C. Overall, the model provides a useful tool for evaluating the design and operation of a thermal storage refrigerator
Modelling of a thermal storage refrigerator
The paper investigates the effect of adding a phase change material in thermal contact with the evaporator in a natural convection domestic refrigerator. The enthalpy method has been applied to investigate the heat release and storage rate of encapsulated ice. The effect of three parameters was investigated by the numerical method: PCM thickness, ambient temperature and evaporating temperature. The results showed that the melting and freezing time increased proportionally with PCM thickness. The refrigerator autonomy was reduced by 48% when the ambient temperature was increased from 20°C to 43°C and the freezing time increased by 27% when the evaporating temperature was reduced from -10°C to -15°C.
A CFD simulation of the airflow and temperature distribution in the natural convection refrigerator was carried out to evaluate the most effective position to place the PCM (top or back wall). The predicted airflow patterns and temperature profiles were considerably different for the two PCM orientations. The predicted air temperature was above 5ºC, thus a eutectic PCM may be required to reduce the temperature in the refrigerator compartment
Mode-coupling and the pygmy dipole resonance in a relativistic two-phonon model
A two-phonon version of the relativistic quasiparticle time blocking
approximation (RQTBA-2) represents a new class of many-body models for nuclear
structure calculations based on the covariant energy density functional. As a
fully consistent extension of the relativistic quasiparticle random phase
approximation (RQRPA), the two-phonon RQTBA implies a fragmentation of nuclear
states over two-quasiparticle and two-phonon configurations. This leads, in
particular, to a splitting-out of the lowest 1 state as a member of the
two-phonon quintuplet from the RQRPA pygmy dipole mode, thus
establishing a physical mixing between these three modes. The inclusion of the
two-phonon configurations in the model space allows to describe the positions
and the reduced transition probabilities of the lowest 1 states in isotopes
Sn as well as the low-energy fraction of the dipole strength
without any adjustment procedures. The model is also applied to the low-lying
dipole strength in neutron-rich Ni isotopes. Recent experimental
data for Ni are reproduced fairly well
Radiocarbon and blue optically stimulated luminescence chronologies of the Oitavos consolidated dune (Western Portugal)
The dune of Oitavos, the underlying paleosol, and Helix sp. gastropod shells found within the paleosol were dated using a combination of radiocarbon and blue optically stimulated luminescence (OSL). The organic component of the paleosol produced a significantly older age (~20,000 cal BP) than the OSL age measurement (~15,000 yr), while 14C age measurements on the inorganic component and the gastropods produced ages of ~35,000 yr and ~34,000 yr, respectively. Rare-earth
element analyses provide evidence that the gastropods incorporate geological carbonate, making them an unreliable indicator of the age of the paleosol. We propose that the 14C age of the small organic component of the paleosol is also likely to be unreliable due to incorporation of residual material. The OSL age measurement of the upper paleosol (~15,000 yr) is consistent with the age for the base of the dune (~14,500 yr). The younger OSL age for the top of the dune (~12,000 yr) suggests that it was built up by at least 2 sand pulses or that there was a remobilization of material at the top during its evolution, prior to consolidation
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