200 research outputs found
Simulation of High Conversion Efficiency and Open-circuit Voltages Of {\alpha}-si/poly-silicon Solar Cell
The P+ {\alpha}-Si /N+ polycrystalline solar cell is molded using the AMPS-1D
device simulator to explore the new high efficiency thin film poly-silicon
solar cell. In order to analyze the characteristics of this device and the
thickness of N+ poly-silicon, we consider the impurity concentration in the N+
poly-silicon layer and the work function of transparent conductive oxide (TCO)
in front contact in the calculation. The thickness of N+ poly-silicon has
little impact on the device when the thickness varies from 20 {\mu}m to 300
{\mu}m. The effects of impurity concentration in polycrystalline are analyzed.
The conclusion is drawn that the open-circuit voltage (Voc) of P+ {\alpha}-Si
/N+ polycrystalline solar cell is very high, reaching 752 mV, and the
conversion efficiency reaches 9.44%. Therefore, based on the above optimum
parameters the study on the device formed by P+ {\alpha}-Si/N+ poly-silicon is
significant in exploring the high efficiency poly-silicon solar cell.Comment: 8 pages 6figures, 1 table
Analysis of Granular Flow in a Pebble-Bed Nuclear Reactor
Pebble-bed nuclear reactor technology, which is currently being revived
around the world, raises fundamental questions about dense granular flow in
silos. A typical reactor core is composed of graphite fuel pebbles, which drain
very slowly in a continuous refueling process. Pebble flow is poorly understood
and not easily accessible to experiments, and yet it has a major impact on
reactor physics. To address this problem, we perform full-scale,
discrete-element simulations in realistic geometries, with up to 440,000
frictional, viscoelastic 6cm-diameter spheres draining in a cylindrical vessel
of diameter 3.5m and height 10m with bottom funnels angled at 30 degrees or 60
degrees. We also simulate a bidisperse core with a dynamic central column of
smaller graphite moderator pebbles and show that little mixing occurs down to a
1:2 diameter ratio. We analyze the mean velocity, diffusion and mixing, local
ordering and porosity (from Voronoi volumes), the residence-time distribution,
and the effects of wall friction and discuss implications for reactor design
and the basic physics of granular flow.Comment: 18 pages, 21 figure
A stochastic flow rule for granular materials
There have been many attempts to derive continuum models for dense granular
flow, but a general theory is still lacking. Here, we start with Mohr-Coulomb
plasticity for quasi-2D granular materials to calculate (average) stresses and
slip planes, but we propose a "stochastic flow rule" (SFR) to replace the
principle of coaxiality in classical plasticity. The SFR takes into account two
crucial features of granular materials - discreteness and randomness - via
diffusing "spots" of local fluidization, which act as carriers of plasticity.
We postulate that spots perform random walks biased along slip-lines with a
drift direction determined by the stress imbalance upon a local switch from
static to dynamic friction. In the continuum limit (based on a Fokker-Planck
equation for the spot concentration), this simple model is able to predict a
variety of granular flow profiles in flat-bottom silos, annular Couette cells,
flowing heaps, and plate-dragging experiments -- with essentially no fitting
parameters -- although it is only expected to function where material is at
incipient failure and slip-lines are inadmissible. For special cases of
admissible slip-lines, such as plate dragging under a heavy load or flow down
an inclined plane, we postulate a transition to rate-dependent Bagnold
rheology, where flow occurs by sliding shear planes. With different yield
criteria, the SFR provides a general framework for multiscale modeling of
plasticity in amorphous materials, cycling between continuum limit-state stress
calculations, meso-scale spot random walks, and microscopic particle
relaxation
Signatures of granular microstructure in dense shear flows
Granular materials react to shear stresses differently than do ordinary
fluids. Rather than deforming uniformly, materials such as dry sand or
cohesionless powders develop shear bands: narrow zones containing large
relative particle motion leaving adjacent regions essentially rigid[1,2,3,4,5].
Since shear bands mark areas of flow, material failure and energy dissipation,
they play a crucial role for many industrial, civil engineering and geophysical
processes[6]. They also appear in related contexts, such as in lubricating
fluids confined to ultra-thin molecular layers[7]. Detailed information on
motion within a shear band in a three-dimensional geometry, including the
degree of particle rotation and inter-particle slip, is lacking. Similarly,
only little is known about how properties of the individual grains - their
microstructure - affect movement in densely packed material[5]. Combining
magnetic resonance imaging, x-ray tomography, and high-speed video particle
tracking, we obtain the local steady-state particle velocity, rotation and
packing density for shear flow in a three-dimensional Couette geometry. We find
that key characteristics of the granular microstructure determine the shape of
the velocity profile.Comment: 5 pages, incl. 4 figure
In the eye of the beholder:promoting learner-centric design to develop mobile games for learning
Out of the project EMuRgency a game-based learning environment evolved, which trains school children in providing reanimation and cardiopulmonary resuscitation (CPR). The application gets players to act as if they were in a real case of emergency. This paper reports on a formal usability study conducted with two different groups of learners, regular learners and learners with special educational needs (SEN). With the study we compared the two groups of learners with regard to game usability and effectiveness of the intervention. Our intention was to better understand the different needs and requirements to learning materials that game designer need to take into consideration in order to make the learning experience successful for both groups. A total of 89 children played the game simulation. Results showed differences in perception and effectiveness of individual mechanisms for the two groups with regard to usability or switching between tasks and mobile device.This publication was partly financed by the European Regional Development Fund (ERDF), regions of the Euregio Meuse-Rhine and the participating institutions under the INTERREG IVa program (EMR.INT4-1.2.-2011-04/070, http://www.emurgency.eu)
CENGO: a web-based serious game to increase the programming knowledge levels of computer engineering students
In recent years, games are used to increase the level of knowledge and experience of individuals working in different domains. Especially in the education field, there are several different serious games
to teach the subjects of the lectures or other educational materials to
students in an enjoyable way. Hence, this study proposes a quantitative
research approach to increase the programming knowledge levels of the
first-year undergraduate students at computer engineering departments.
For this aim, a responsive web platform was developed to teach the syntax and logic of C programming language by using some game elements.
Therefore, the students have a chance to repeat the topics related to C
programming language continuously since the platform is always accessible. To figure out the efficiency of the designed environment, 10 first-year
computer engineering students were selected. According to the results obtained from the user tests, this game can be used as an educational tool,
which supports the traditional training methods, to increase the knowledge levels of students about the syntax and logic of C programming
language
Use of the microalga Scenedesmus obliquus to remove cadmium cations from aqueous solutions
The ability of a wild strain of Scenedesmus
obliquus, isolated from a heavy metal-contaminated environment, to remove Cd2+ from aqueous solutions was studied at several initial concentrations. Viable biomass removed metal to a maximum extent of 11.4 mgCd/g at 1 mgCd/l, with most Cd2+ being adsorbed onto the cell surface. A commercially available strain (ACOI 598) of the same microalga species was also exposed to the same Cd concentrations, and similar results were obtained for the maximum extent of metal removal. Heat-inactivated cells
removed a maximum of 6.04 mgCd/g at 0.5 mgCd/l. The highest extent of metal removal, analyzed at various pH values, was 0.09 mgCd/g at pH 7.0. Both strains of the
microalga tested have proven effective in removing a toxic heavy metal from aqueous solutions, hence supporting their choice for bioremediation strategies of industrial effluents.info:eu-repo/semantics/acceptedVersio
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