Super‐Efficient Exciton Funneling in Layer‐by‐Layer Semiconductor Nanocrystal Structures

In semiconductor nanocrystals the electronic energy gap is determined not only by the material but also by the size of the nanocrystals. This allows the construction of an energy‐gap gradient normal to multiple layers of nanocrystals where the diameters of the nanocrystals are monotonically increasing or decreasing in subsequent layers. In such devices we observe a highly efficient funneling of excitation energy from layers comprising smaller nanocrystals towards the layer with the largest nanocrystals in the center of the funnel. Most importantly, not only are excitons in radiative states transferred, but also excitons from trapped states, usually lost for luminescence, can be effectively recycled, hence increasing the overall luminescence yield.     

Selective adsorption of solvents in a multiscale device

We have incorporated microspheres, from 50 to 80 μm in diameter, of periodic mesoporous organosilica (inner surfaces up to 1,000 m²/g and pore sizes in the nanometre range) with two types of organic functionalities (benzene and ethane bridges, respectively) inside microstructured channels (each 200 μm wide and 100 μm deep) and, exemplarily, monitored by Raman microscopy (Raman spectroscopy through microscope optics) that the temperature characteristics of the adsorption–desorption equilibria of benzene and ethanol vary significantly with the type of organic functionality of the microspheres and the pore morphology. The integration of this class of nanostructured material into devices by means of microchannels is a promising novel approach to, among others, substance separation in analytics, micro process engineering, and micro chemistry.     

Wide Baseline Matching between Unsynchronized Video Sequences

3D reconstruction of a dynamic scene from features in two cameras usually requires synchronization and correspondences between the cameras. These may be hard to achieve due to occlusions, different orientation, different scales, etc. In this work we present an algorithm for reconstructing a dynamic scene from sequences acquired by two uncalibrated non-synchronized fixed affine cameras. It is assumed that (possibly) different points are tracked in the two sequences. The only constraint relating the two cameras is that every 3D point tracked in one sequence can be described as a linear combination of some of the 3D points tracked in the other sequence. Such constraint is useful, for example, for articulated objects. We may track some points on an arm in the first sequence, and some other points on the same arm in the second sequence. On the other extreme, this model can be used for generally moving points tracked in both sequences without knowing the correct permutation. In between, this model can cover non-rigid bodies with local rigidity constraints. We present linear algorithms for synchronizing the two sequences and reconstructing the 3D points tracked in both views. Outlier points are automatically detected and discarded. The algorithm can handle both 3D objects and planar objects in a unified framework, therefore avoiding numerical problems existing in other methods. This work was done while the authors were PhD students in the School of Computer Science and Engineering, the Hebrew University of Jerusalem.     

On the Effects of Subgrade Erosion on the Contact Pressure Distribution under Rigid Surface Structures

The performance of rigid surface structures such as concrete pavements and slabs-on-grade supported by a deteriorated subgrade and experiencing local contact loss is investigated experimentally and numerically in this study. A laboratory setup has been designed to facilitate the simulation of subsurface erosion and measure the changes in contact pressure at selected locations under a slab-on-grade supported on granular material. The presence of erosion voids under a slab-on-grade can lead to rapid increase in the contact pressure in the immediate vicinity of the void in addition to an increase in tensile stresses at the outermost fibers of the slab. This preliminary study suggests that efforts to detect and arrest the growth of erosion voids under slabs-on-grade should be made before the voids reach the size where significant loss of support develops and the tensile strength of the slab material is exceeded.     

Thermal Modeling of Hybrid Storage Clusters

There is a lack of thermal models for storage clusters; most existing thermal models do not take into account the utilization of hard drives (HDDs) and solid state disks (SSDs). To address this problem, we build a thermal model for hybrid storage clusters that are comprised of HDDs and SSDs. We start this study by generating the thermal profiles of hard drives and solid state disks. The profiling results show that both HDDs and SSDs have profound impacts on temperatures of storage nodes in a cluster. Next, we build two types of hybrid storage clusters, namely, inter-node and intra-node hybrid storage clusters. We develop a model to estimate the cooling cost of a storage cluster equipped with hybrid storage nodes. The thermal model is validated against data acquired by temperature sensors. Experimental results show that, compared to the HDD-first strategy, the SSD-first strategy is an efficient approach to minimize negative thermal impacts of hybrid storage clusters.     

Influence of Codoping on the Magnetoresistance of Paramagnetic (Ga,Mn)As

We studied the correlation between magnetoresistance (MR) effects and the type of conducti- vity in paramagnetic Ga_1–x Mn _x As with x < 0.5%. Series of samples of (Ga,Mn)As with different codoping levels of Te have been prepared by metal-organic vapor-phase epitaxy (MOVPE). With increasing Mn-content from doping levels to x = 0.5% in paramagnetic Ga_1–x Mn _x As, the MR at 1.6 K changes continuously from positive to strongly negative. This manifests the complex interplay between p–d exchange induced valence band splitting and the metal–insulator transition. Codoping with Te leads eventually to a dominant conduction band transport. It is characterized by a small negative contribution at low magnetic fields to the parabolic MR similar to that found in highly n-doped diamagnetic semiconductors. It shows that the Mn-induced conduction band splitting is much smaller than the valence band splitting, i.e., |N₀| |N₀|.     

Enantiomeric Control of Intrinsically Chiral Nanocrystals

The chiral aspect of inorganic crystals that crystallize in chiral space groups has been largely ignored until recently, partly due to difficulties in characterizing the chiroptical properties of bulk crystals, and also due to the difficulty in separating (sub)micrometer-scale chiral crystal enantiomers. In recent years, the colloidal synthesis of intrinsically chiral nanocrystals (NCs) of several chiral inorganic compounds with significant enantiomeric excess has been demonstrated. This is achieved through the use of chiral molecular ligands, which bind to the atomic/ionic components of the crystals, preferentially forming one crystal enantiomorph. Here, recent progress on several aspects of these NCs is described, including the connection between ligand structure and its ability to direct NC handedness, chiral amplification in the synthesis leading to enantiopure NC samples, spontaneous symmetry breaking, the formation of NCs with chiral shapes, the connection between lattice and shape chirality and mixed contributions of atomic-scale and shape chirality to the chiroptical properties.     

A Semi-Lagrangian Method for a Fokker-Planck Equation Describing Fiber Dynamics

A simplified Fokker-Planck model for the lay-down of fibers on a conveyor belt in the production process of nonwovens is investigated. It takes into account the motion of the fiber under the influence of turbulence. The emphasis in this paper is on the development of a numerical procedure to solve the model. We present a semi-Lagrangian scheme that accurately captures the fiber dynamics and conserves the mass. The scheme allows large time steps to be taken in numerical simulations and requires moderate computing times to obtain steady state solutions. Numerical results and examples are presented and compared for several selection of fiber parameters. The obtained results show that the semi-Lagrangian method is able to reproduce accurately the time development of functionals of the process that are important for the quality assessment of industrial fibers.     

Generic and reflective graph transformations for checking and enforcement of modeling guidelines

In the automotive industry, the model driven development of software, today considered as the standard paradigm, is generally based on the use of the tool MATLAB Simulink/Stateflow. To increase the quality, the reliability, and the efficiency of the models and the generated code, checking and elimination of detected guideline violations defined in huge catalogs has become an essential task in the development process. It represents such a tremendous amount of boring work that it must necessarily be automated. In the past we have shown that graph transformation tools like Fujaba/MOFLON allow for the specification of single modeling guidelines on a very high level of abstraction and that guideline checking tools can be generated from these specifications easily. Unfortunately, graph transformation languages do not offer appropriate concepts for reuse of specification fragments—a MUST, when we deal with hundreds of guidelines. As a consequence we present an extension of MOFLON that supports the definition of generic rewrite rules and combines them with the reflective programming mechanisms of Java and the model repository interface standard Java Metadata Interface (JMI).