Intersublevel Spectroscopy on Single InAs-Quantum Dots by Terahertz Near-Field Microscopy

Using scattering-type near-field infrared microscopy in combination with a free-electron laser, intersublevel transitions in buried single InAs quantum dots are investigated. The experiments are performed at room temperature on doped self-assembled quantum dots capped with a 70 nm GaAs layer. Clear near-field contrast of single dots is observed when the photon energy of the incident beam matches intersublevel transition energies, namely the p-d and s-d transition of conduction band electrons confined in the dots. The observed room-temperature line width of 5-8 meV of these resonances in the mid-infrared range is significantly below the inhomogeneously broadened spectral lines of quantum dot ensembles. The experiment highlights the strength of near-field microspectroscopy by demonstrating signals from bound-to-bound transitions of single electrons in a probe volume of the order of (100 nm)(3).     

Synthesis of hydroxyapatite nanoparticles with tailorable morphologies and carbonate substitutions using a wet precipitation method

Hydroxyapatite (HA) nanoparticles with different morphologies and variant levels of carbonate substitutions were synthesized using a wet precipitation method by adjusting the heating temperature and/or the initial ion concentration of the reaction system. Within the particles, crystalline domains with different lengths were aligned along each other and formed into nanoparticles with different sizes, shapes and topographies. Different from most reported studies, the nucleation, growth and morphology of the crystalline domains were found sensitive to heating temperature, but not significantly influenced by initial ion concentration within the studied range. The OH- and PO4(3-) ions within the HA particles were partially substituted by CO3(2-) ions. The substitution was dominated by the replacement of OH- instead of PO4(3-) in HA. The carbonate substitution was found to decrease with increasing heating temperature and/or initial ion concentration. Therefore, both the morphology and composition of the HA particles can be tailored by controlling the heating temperature and/or the initial ion concentration in the reaction system. Such synthesized HA nanoparticles can be used as biomaterials for bone tissue engineering.     

Early and late selection in unconscious information processing.

In four experiments, we investigated whether masked stimuli in priming experiments are subjected to early or to late selection. In Experiment 1, participants classified four target-pictures as being small or large. In line with early selection accounts, prime-pictures with a different perceptual appearance as the experienced targets did not elicit congruency effect. In Experiment 2, 40 targets all depicting animals were presented. Results were in line with late selections assumptions because novel animal primes but not novel primes from different semantic categories yielded congruency effects. In Experiment 3, the targets were chosen such that there is a second semantic feature that covaried with the required response. Here, novel primes picturing small animals did not influence target responses with regard to the instructed size classification, but with regard to their affiliation to the category animal. In Experiment 4, small and large pictures from two categories were presented. Category match did not influence priming, ruling out that feature overlap contaminated the former results. The results indicate that participants’ prestimulus expectations determine in which stage in the processing-stream masked stimuli are selected. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Junction and Drop-Shaft Boundary Conditions for Modeling Free-Surface, Pressurized, and Mixed Free-Surface Pressurized Transient Flows

A junction and drop-shaft boundary conditions (BCs) for one-dimensional modeling of transient flows in single-phase conditions (pure liquid) are formulated, implemented and their accuracy are evaluated using two computational fluid dynamics (CFD) models. The BCs are formulated in the case when mixed flows are simulated using two sets of governing equations, the Saint-Venant equations for the free-surface regions and the compressible water hammer equations for the pressurized regions. The proposed BCs handle all possible flow regimes and their combinations. The flow in each pipe can range from free surface to pressurized flow and the water depth at the junction or drop shaft can take on all possible levels. The BCs are applied to the following three cases: (1) a three-way merging flow; (2) a three-way dividing flow; and (3) a drop shaft connected to a single-horizontal pipe subjected to a rapid variation of the water surface level in the drop shaft. The flow regime for the first two cases range from free surface to pressurized flows, while for the third case, the flow regime is pure pressurized flow. For the third case, laboratory results as well as CFD results were used for evaluating its accuracy. The results suggest that the junction and drop-shaft BCs can be used for modeling transient free-surface, pressurized, and mixed flow conditions with good accuracy.     

Continuous production of flexible carbon nanotube-based transparent conductive films

This work shows a simple, single-stage, scalable method for the continuous production of high-quality carbon nanotube-polymer transparent conductive films from carbon feedstock. Besides the ease of scalability, a particular advantage of this process is that the concentration of nanotubes in the films, and thus transparency and conductivity, can be adjusted by changing simple process parameters. Therefore, films can be readily prepared for any application desired, ranging from solar cells to flat panel displays. Our best results show a surface resistivity of the order of 300 Ω square^-1 for a film with 80% transparency, which is promising at this early stage of process development.     

Microstructure and corrosion behaviour of pulsed plasma-nitrided AISI H13 tool steel

The effect of pulsed plasma nitriding temperature and time on the pitting corrosion behaviour of AISI H13 tool steel in 0.9% NaCl solutions was investigated by cyclic polarization. The pitting potential (E_pit) was found to be dependent on the composition, microstructure and morphology of the surface layers, whose properties were determined by X-ray diffraction and scanning electron microscopy techniques. The best corrosion protection was observed for samples nitrided at 480 °C and 520 °C. Under such experimental conditions the E_pit-values shifted up to 1.25 V in the positive direction.     

Modelling brittle crack formation at geometrical and material discontinuities using a finite fracture mechanics approach

In this study, finite fracture mechanics procedures are employed to predict crack formation at geometrical and material discontinuities in brittle elastic structures. A hybrid failure model is utilised taking into account the stress field in the undamaged structure and the energy balance for the formation of cracks. Asymptotic formulations are compared to a direct numerical implementation. Experiments carried out on notched brittle specimens exhibiting various geometries and loading-modes are analysed by means of both approaches. Additionally, free-edge effects in composite laminates are analysed. It is found that the predictions from the model agree well with experimental results.     

Application of a response surface method to the optimal design of the wall temperature profiles in extrusion die

A new approach to the optimal design of the die wall temperature profile in polymer extrusion processes is presented. In this approach, optimization of the design variables is conducted by a Response Surface Method (RSM) and the Sequential Quadratic Programming (SQP) algorithm. Design of experiment (DoE) needed for the construction of the response surface is used to evaluate the objective and the constraint functions on the basis of a finite element method (FEM). Two designs of experiments are used and the performances of the optimization results are compared with respect to efficiency and ability to obtain a global optimum. Typically, for extrusion die design, the objective function states that the average velocity across the die exit is uniform. Constraints are used to limit the pressure drop in the die. For this purpose, we optimize the wall temperature profile of a coat hanger die in a heterogeneous way, (i.e. the wall temperature may not be constant in the entire die). The melt temperature enables us to locally control the viscosity, which influences the flows in the various zones. The effect of the design variables in the objective and constraint functions is investigated using Taguchi method. The flow analysis results are then combined with an automatic optimization algorithm to provide a new profile of the die wall temperature distributions.     

Experimental study of gas engine driven air to water heat pump in cooling mode

Nowadays a sustainable development for more efficient use of energy and protection of the environment is of increasing importance. Gas engine heat pumps represent one of the most practicable solutions which offer high energy efficiency and environmentally friendly for heating and cooling applications. In this paper, the performance characteristics of gas engine driven heat pump used in water cooling were investigated experimentally without engine heat recovery. The effects of several important factors (evaporator water inlet temperature, evaporator water volume flow rate, ambient air temperature, and engine speed) on the performance of gas engine driven heat pump were studied in a wide range of operating conditions. The results showed that primary energy ratio of the system increased by 22.5% as evaporator water inlet temperature increased from 13 °C to 24 °C. On the other hand, varying of engine speed from 1300 rpm to 1750 rpm led to decrease in system primary energy ratio by 13%. Maximum primary energy ratio has been estimated with a value of two over a wide range of operating conditions.     

Experiment-driven electrochemical modeling and systematic parameterization for a lithium-ion battery cell

This paper presents a novel electrochemical lithium-ion cell model which can be used in battery control units. Based on classical single-particle approaches, a lumped-parameter nonlinear model is developed that is able to predict accurately the terminal voltages for arbitrary loads, and even for potentiostatic operation. The key points are: (1) an incorporation of the electrolyte potential, (2) a modal decomposition of the partial differential equation of the liquid phase lithium-ion concentration, (3) a correct handling of the SOC-dependent diffusivity in the insertion materials of both electrodes, and (4) a consideration of temperature-dependent kinetic processes. A combined parameter analysis and identification is successfully applied for the parameterization of the model. Using a Fisher-information matrix approach in combination with a sensitivity analysis, the identifiability of each parameter is estimated in dependence on the measurement information. Using this information, it is possible to choose a small number of relevant experiments which are sufficient to fully parameterize the model.