The kinematics of the swing phase obtained from accelerometer and gyroscope measurements

The kinematics needed to calculate the knee moment during the initial swing phase were obtained from a set of eight leg-mounted uni-axial accelerometers and two gyroscopes. The angular and linear accelerations of shank and thigh were calculated from the signals of two accelerometers mounted on each of the leg segments directed tangentially and radially to the movement. The angular velocities of shank and thigh were measured by the gyroscopes. The absolute angles of shank and thigh were obtained by integration of the gyroscope signal plus an added offset angle, estimated from radial and tangential accelerometer signals registered while standing. Movement was assumed to be in the saggital plane. The accuracy of the quantities found from the leg mounted sensors was calculated in terms of correlation and the RMS error by comparing against measurements obtained by a VICONTM system. The results were indistinguishable. The system was later applied in research measurement

Thermally controlled widening of droplet etched nanoholes

We describe a method to control the shape of nanoholes in GaAs (001) which combines the technique of local droplet etching using Ga droplets with long-time thermal annealing. The cone-like shape of inverted nanoholes formed by droplet etching is transformed during long-time annealing into widened holes with flat bottoms and reduced depth. This is qualitatively understood using a simplified model of mass transport incorporating surface diffusion and evaporation. The hole diameter can be thermally controlled by varying the annealing time or annealing temperature which provides a method for tuning template morphology for subsequent nanostructure nucleation. We also demonstrate the integration of the combined droplet/thermal etching process with heteroepitaxy by the thermal control of hole depth in AlGaAs layers

Single-dot Spectroscopy of GaAs Quantum Dots Fabricated by Filling of Self-assembled Nanoholes

We study the optical emission of single GaAs quantum dots (QDs). The QDs are fabricated by filling of nanoholes in AlGaAs and AlAs which are generated in a self-assembled fashion by local droplet etching with Al droplets. Using suitable process parameters, we create either uniform QDs in partially filled deep holes or QDs with very broad size distribution in completely filled shallow holes. Micro photoluminescence measurements of single QDs of both types establish sharp excitonic peaks. We measure a fine-structure splitting in the range of 22–40μeV and no dependence on QD size. Furthermore, we find a decrease in exciton–biexciton splitting with increasing QD size

Quantized Dispersion of Two-Dimensional Magnetoplasmons Detected by Photoconductivity Spectroscopy

We find that the long-wavelength magnetoplasmon, resistively detected by photoconductivity spectroscopy in high-mobility two-dimensional electron systems, deviates from its well-known semiclassical nature as uncovered in conventional absorption experiments. A clear filling-factor dependent plateau-type dispersion is observed that reveals a so far unknown relation between the magnetoplasmon and the quantum Hall effect.Comment: 5 pages, 3 figure

Slow roll: A longitudinal analysis of sustainable energy implementation

The importance of adopting sustainable practices in the tourism industry is well established but widespread implementation is still wanting. Institutional theory framed an assessment of tourism professionals’ perceptions of constraints and benefits to sustainable practices, as well as actual implementation of energy practices between 2007 and 2016. Perceptions and practices were tracked through an Internet-based questionnaire among professionals in three-year intervals in a Midwestern U.S state. Professionals consistently agreed that attracting new clientele, improving consumer perceptions, and organizational image were benefits of sustainable practices, while initial financial costs constrained implementation. The most frequently implemented energy practices were using daylight and compact fluorescent light bulbs (CFL). Overall, adoption of sustainable practices was varied and implementation rates remained minimally changed. Reasons for the varied adoption and lack of change may be explained by perceived lack of resources, consistent with organizational capacity, or lack of pressure from socio-cultural environment, per institutional theor

Optical Properties of GaAs Quantum Dots Fabricated by Filling of Self-Assembled Nanoholes

Experimental results of the local droplet etching technique for the self-assembled formation of nanoholes and quantum rings on semiconductor surfaces are discussed. Dependent on the sample design and the process parameters, filling of nanoholes in AlGaAs generates strain-free GaAs quantum dots with either broadband optical emission or sharp photoluminescence (PL) lines. Broadband emission is found for samples with completely filled flat holes, which have a very broad depth distribution. On the other hand, partly filling of deep holes yield highly uniform quantum dots with very sharp PL lines

Gain in Three-Dimensional Metamaterials utilizing Semiconductor Quantum Structures

We demonstrate gain in a three-dimensional metal/semiconductor metamaterial by the integration of optically active semiconductor quantum structures. The rolling-up of a metallic structure on top of strained semiconductor layers containing a quantum well allows us to achieve a three-dimensional superlattice consisting of alternating layers of lossy metallic and amplifying gain material. We show that the transmission through the superlattice can be enhanced by exciting the quantum well optically under both pulsed or continuous wave excitation. This points out that our structures can be used as a starting point for arbitrary three-dimensional metamaterials including gain

Congruent evaporation temperature of molecular beam epitaxy grown GaAs (001) determined by local droplet etching

The congruent evaporation temperature Tc of GaAs (001) is critical for many technological processes and is fundamental to the control and stability of Ga droplets for quantum structure fabrication. We apply the technique of local droplet etching (LDE) to measure Tc for technologically important molecular beam epitaxy (MBE) grown GaAs (001). Below Tc, Ga droplets deposited on the surface shrink and form nanoholes via LDE and thermal widening. Above Tc, droplets grow by capturing excess Ga. From the transition between both regimes, we determine Tc = 680 ± 10 °C. Additionally, we find that the nanohole/droplet densities follow an Arrhenius-type temperature dependence with an activation energy of 1.31 eV. The method probes the stability of pre-existing droplets formed by deposition and so avoids the complication of nucleation barriers and readily allows the measurement of Tc for technologically important planar GaAs surfaces in any standard MBE system. The authors thank S. Schnüll for MBE growth and the Deutsche Forschungsgemeinschaft for financial support via HA 2042/6-1. D.E.J. acknowledges the support from a Marie Curie International Incoming Fellowship

Measurement of length distribution of beta-lactoglobulin fibrils by multiwavelength analytical ultracentrifugation

The whey protein beta-lactoglobulin is the building block of amyloid fibrils which exhibit a great potential in various applications. These include stabilization of gels or emulsions. During biotechnological processing, high shear forces lead to fragmentation of fibrils and therefore to smaller fibril lengths. To provide insight into such processes, pure straight amyloid fibril dispersions (prepared at pH 2) were produced and sheared using the rotor stator setup of an Ultra Turrax. In the first part of this work, the sedimentation properties of fragmented amyloid fibrils sheared at different stress levels were analyzed with mulitwavelength analytical ultracentrifugation (AUC). Sedimentation data analysis was carried out with the boundary condition that fragmented fibrils were of cylindrical shape, for which frictional properties are known. These results were compared with complementary atomic force microscopy (AFM) measurements. We demonstrate how the sedimentation coefficient distribution from AUC experiments is influenced by the underlying length and diameter distribution of amyloid fibrils. In the second part of this work, we show how to correlate the fibril size reduction kinetics with the applied rotor revolution and the resulting energy density, respectively, using modal values of the sedimentation coefficients obtained from AUC. Remarkably, the determined scaling laws for the size reduction are in agreement with the results for other material systems, such as emulsification processes or the size reduction of graphene oxide sheets.</p