Search results for "Oscillation"
showing 10 items of 1257 documents
Transient response in nonlinear region of molten polymers subjected to a sudden imposition of constant shear stress or constant electric field
1980
Experimental transient results in the nonlinear region are reported for a commercial polyisobutylene subjected to sudden imposition of either a constant shear stress or a constant electric field. Some steady-state results, eventually obtained in different types of experiments, are also considered. In both cases, a model analysis is presented that accounts for the nonlinear effects through changes in the free volume depending upon the applied stress. The good comparison between theoretical predictions and experimental results seems to indicate that the phenomenological approach advanced here is very promising.
Assigning ionic properties in perovskite solar cells; a unifying transient simulation/experimental study
2021
Kinetic modelling has proven to be essential to understand the time and spatial dependence of charge carriers in solar cells. Traditional drift–diffusion simulations have generally been employed to describe static steady-state conditions, whereas recently the transient counterpart has been able to reveal more detailed information regarding carrier kinetics. In addition to customary electron and hole dynamics, perovskite materials are known to also be strongly affected by the displacement of lattice vacancies, charged atoms or even entire molecules. Such ionic motion transpires on vastly different time scales compared to free charges and are generally not straightforward to simultaneously ac…
Transient Moiré rotation patterns in thin colloidal crystals
2010
A high resolution optical microscopy study on low salt charged sphere suspensions settling under gravity reveals the formation of AB-stacked triangular layers via different transient structures. In particular, metastable triangular Moire rotation patterns (formally corresponding to 1 × 1 Rα super structures) with rotation angles α = 27.8° and α = 38.2° are identified.
Numerical study of transient behaviour of molten zone during industrial FZ process for large silicon crystal growth
2004
The fully transient axisymmetric model has been developed for calculation of phase boundaries in large (up to 200 mm diameter) industrial floating zone (FZ) silicon single crystal growth with the needle-eye technique. The transient model is implemented in a specialized computer program. The model and program are based on a previously developed model and program for steady-state FZ process calculations. This transient approach allows studying of such substantially time-dependent process phases as the growth of the starting and ending cones of the crystal rod, which are particularly important for growth of large crystals in practice. Numerous calculations are carried out and the results for r…
Crystal shape 2D modeling for transient CZ silicon crystal growth
2013
Abstract A non-stationary axisymmetric model of Czochralski silicon single crystal growth is presented. The model describes transient behavior of crystal–melt, melt–gas and crystal–gas interfaces in connection with PID-based control of crystal diameter by changing crystal pulling velocity and heater power. To calculate significant crystal shape changes, unstructured finite element mesh is used in crystal and melt together with automatic element size control. Heater temperature changes are modeled with a simplified integral model. A numerical simulation example of start cone growth is given.
Steady state and transient thermal-hydraulic characterization of full-scale ITER divertor plasma facing components
2008
Abstract In the frame of the activities related to ITER divertor R&D, ENEA CR Brasimone was in charge by EFDA (European Fusion Development Agreement) to investigate the thermal-hydraulic behaviour of the full-scale divertor plasma facing components, i.e. the outer vertical target, the inner vertical target and the dome-liner, both in steady state and during draining and drying transient. The investigation was performed by means of both experimental test campaigns performed at ENEA CR Brasimone and theoretical simulation developed in RELAP5 Mod.3.3 environment at the Department of Nuclear Engineering of the University of Palermo (DIN). This paper presents the achieved experimental results fo…
On the theoretical–numerical study of the ITER Upper Port Plug structure hydraulic behaviour under steady state and draining and drying transient con…
2011
Abstract The ITER diagnostic Upper Port Plug (UPP) is a water-cooled stainless steel structure aimed to integrate within vacuum vessel the plasma diagnostic systems, shielding them from neutron and photon irradiation. Due to the very intense heat loads expected, a proper cooling circuit has been designed to ensure an adequate UPP cooling with an acceptable thermal rise and an unduly high pumping power and to perform its draining and drying procedure by injection of pressurized nitrogen. A theoretical research activity has been launched at the Department of Nuclear Engineering of the University of Palermo aiming to investigate the hydraulic behaviour of the UPP Trapezoid Section cooling circ…
Peltier cells as temperature control elements: Experimental characterization and modeling
2014
Abstract The use of Peltier cells to realize compact and precise temperature controlled devices is under continuous extension in recent years. In order to support the design of temperature control systems, a simplified modeling of heat transfer dynamics for thermoelectric devices is presented. By following a macroscopic approach, the heat flux removed at the cold side of Peltier cell can be expressed as Q ˙ c = γ ( T c − T c eq ) , where γ is a coefficient dependent on the electric current, Tc and T c eq are the actual and steady state cold side temperature, respectively. On the other hand, a microscopic modeling approach was pursued via finite element analysis software packages. To validat…
Continuous wave dual-wavelength operation at 1048 and 1386 nm in Nd<sup>3+</sup>:LaBGeO<inf>5</inf> for yellow laser light ge…
2007
We present results on simultaneous oscillation in continuous-wave at 1048 and 1386 nm in Nd3+:LaBGeO5 crystal. LaBGeO5 is a nonlinear positive uniaxial crystal with potential application for intracavity generation of yellow laser radiation at 597 nm. Due to the different cross section in both laser channels, simultaneous oscillation is achieved by axial hole burning in a standing wave (linear cavity). It is concluded that a stable output laser spectrum is obtained for an absorbed pump power of 700 mW. A laser competition with alternating single-channel and dual-channel oscillation at different pump regimes was observed in the experiments.
Ab Initio Simulation of Attosecond Transient Absorption Spectroscopy in Two-Dimensional Materials
2018
We extend the first-principles analysis of attosecond transient absorption spectroscopy to two-dimensional materials. As an example of two-dimensional materials, we apply the analysis to monolayer hexagonal boron nitride (h-BN) and compute its transient optical properties under intense few-cycle infrared laser pulses. Nonadiabatic features are observed in the computed transient absorption spectra. To elucidate the microscopic origin of these features, we analyze the electronic structure of h-BN with density functional theory and investigate the dynamics of specific energy bands with a simple two-band model. Finally, we find that laser-induced intraband transitions play a significant role in…