Localized irradiation effects on tunnel diode transitions in multi-junction concentrator solar cells

Multi-junction concentrator solar cells incorporate tunnel diodes that undergo a transition from high-conductance tunneling to low-conductance thermal diffusion behavior, typically at threshold current densities of the order of 10²-10³ mA/mm². We present experimental evidence of a prominent heretofore unrecognized dependence of threshold current density on the degree of localized irradiation, in different solar cell architectures. We also show that solar cells with non-uniform metallization can exhibit an additional spatial dependence to the tunnel diode threshold current density. These previously undiscovered phenomena - which should be observable in all non-uniformly irradiated photovoltaic tunnel diodes - are interpreted as being derived from the lateral spreading of excess majority carriers (analogous to current spreading in light-emitting diodes (LEDs)). The consequences for concentrator photovoltaics are addressed.     

Analytical Ground-Water Flow Solutions for Channel-Aquifer Interaction

A general solution scheme for determining ground-water levels for channel∕group-water systems with recharge is developed and verified. The analytical solution uses the Laplace transform method to solve a linearized form of the Boussinesq equation. Unlike other solutions, this scheme allows for both boundaries and sources∕sinks to vary as a function of time and space. To verify the analytical scheme, three one-dimensional case studies of flow between two line sources in an unconfined aquifer were explored through a base run and a set of sensitivity analyses. These runs involved comparisons to MODFLOW and changes in the boundary conditions and dimensions. As noted, the flow equations were linearized about a point called the representative flow depth. A value of havg, defined as the average water depth between the initial and steady flow conditions, was used as the representative flow depth. Results of the proposed method matched very well with MODFLOW solutions for all times and locations using an optimal linearization point. In addition, using havg improved the solutions compared to those obtained previously.     

A Brownian control problem for a simple queueing system in the Halfin–Whitt regime

We consider a formal diffusion limit for a control problem of a multi-type multi-server queueing system, in the regime proposed by Halfin and Whitt. This takes the form of a control problem where the dynamics are driven by a Brownian motion. In one dimension, a pathwise minimum is obtained and is characterized as the solution to a stochastic differential equation. The pathwise solution to a special multi-dimensional problem (corresponding to a multi-type system) follows.     

Numerical Study of Particle Motion in Jet Milling

Jet mills are common devices used in industry for fine milling of dry particulate materials. The size reduction is caused by repeated events of impacts between particles. Although many parameters affect the performance of a jet mill, only a few of them were investigated. Particles' motions in a jet mill have great influence on the comminution process and energy consumption. Therefore, as a first step for a full simulation of the jet-mill process, it was decided to investigate the particle motion inside the jet mill by neglecting particle-particle interaction and particle breakage. In this way, the numerical simulations provide a better understanding of the classification process. In the present study, three-dimensional numerical simulations of particle motion in an industrial full-scale jet mill were conducted. The predictions of the numerical simulations were compared with experimental data and used to analyze the flow field characteristics.     

Optimal operation of multiquality water distribution systems: unsteady conditions

This paper describes the methodology and application of a genetic algorithm scheme tailor-made to EPANET, for optimizing the operation of a water distribution system under unsteady water quality conditions. The water distribution system consists of sources of different qualities, treatment facilities, tanks, pipes, control valves, and pumping stations. The objective is to minimize the total cost of pumping and treating the water for a selected operational time horizon, while delivering the consumers the required quantities at acceptable qualities and pressures. The decision variables for each of the time steps that encompass the total operational time horizon include: the scheduling of the pumping units, settings of the control valves, and treatment removal ratios at the treatment facilities. The constraints are: head and concentrations at the consumer nodes, maximum removal ratios at the treatment facilities, maximum allowable amounts of water withdrawals at the sources, and returning at the end of the operational time horizon to a prescribed total volume in the tanks. The model is explored through two example applications.     

An extended cell-average technique for a multi-dimensional population balance of granulation describing aggregation and breakage

This paper focuses on obtaining the numerical solution to a three-dimensional population balance model (PBM) of granulation using the cell-average technique first proposed by [22]. Conventionally, linear grids are used for the solution of PBMs, but the ability to incorporate non-linear grids would be more advantageous given that a larger size range can be covered using fewer number of grids, thus reducing computational overhead. Furthermore, the use of linear representation of grids in PBMs to represent industrial granulation processes that span a wide granule size range is computationally prohibitive and results show that a non-linear grid representation is computationally more efficient with comparable accuracy. Parallelization of the PBM via a multi-core strategy has also been incorporated in order to reduce the simulation time of the model. Incorporating the cell average technique along with parallelization of the overall model lends credence to the overall use of the model for effective granulation process design and analysis.     

Thermally-induced protein–polyphenol co-assemblies: beta lactoglobulin-based nanocomplexes as protective nanovehicles for EGCG

Delivery of sensitive water-soluble compounds in foods is an important challenge. (−)-Epigallocatechin-3-gallate (EGCG), the major catechin in green tea, is a potent antioxidant with numerous attributed health benefits. However, its sensitivity to oxidation limits its enrichment in the diet for preventive medicine. We have studied the possibility of using thermally modified β-lactoglobulin (β-Lg) to form co-assembled nanovehicles for delivery of EGCG, as a model system for delivery of polyphenols by heat-modified proteins. Using fluorescence spectroscopy, DLS and spectrophotometry we found that optimal nano-entrapment is obtained when EGCG is added to preheated (75–85 °C, 20 min) β-Lg solution during cooling and vortexing. The measured association constant with the heated protein was 3.7 × 10⁵ M⁻¹, about 3.5-fold higher than that with the native protein: 1.05 × 10⁵ M⁻¹. Thermally-induced protein-EGCG co-assemblies were smaller than 50 nm, thus excellent transparency was maintained, enabling their application in clear beverages. These complexes conferred considerable protection to EGCG against oxidative degradation: A 33-fold lower initial degradation rate, and a 3.2-fold slower degradation over 8 days were observed for nano-entrapped compared to unprotected EGCG.     

Two maternal representations: A study of Israeli adopted children.

Using an object relations perspective, the representations of birth and adopted mothers in a sample of 52 nonreferred adoptees were studied. To better understand the specific effects of adoption or, the construction of 2 maternal representations, birth and adoptive maternal representation of adopted children was compared with that of nonadopted children. In addition, the effect of incongruous representations of birth and adoptive mothers on adoptees' exteralizing and internalizing behaviors was explored. Compared with nonadopted children, adoptees' representations of the mothers appear as more concrete and less benign. Among adopted children, representations of the birth mothers were found to contain split negative aspects of the adoptive mothers. Moreover, the differences between birth and adoptive mother representations were found to associate with adoptees'externalizing behaviors. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Joint transform correlator with spatial code division multiplexing

A joint transform correlator may suffer from overlapping of the zero diffraction order of the output, which does not contain relevant information, and the correlation peaks that appear in the first diffraction orders if objects are not sufficiently separated. Such overlapping significantly reduces the signal-to-noise ratio of the identification process. We propose a novel approach based on code division multiplexing technique in which the contrast of the identification peaks is significantly enhanced. The approach does not include placing the two objects side by side but rather includes code multiplexing them. Moreover, the code division multiplexing technique allows the space-bandwidth product to be improved. Optical implementation results are given.