THERMAL RESPONSE OF SILICON CRYSTAL TO PICO-FEMTOSECOND HEAT PULSE BY MOLECULAR DYNAMICS

We investigate the thermal response of a silicon crystal irradiated by a pico-femto heat pulse by using molecular dynamics technique and a linear response theory–based statistical analysis. The thermal susceptibility is first defined in terms of computed quantities and then convoluted with time Gaussian temperature pulses. The qualitative difference between the responses to various pulse durations is explained and the results are compared to those of classical Fourier model. Non-Fourier behaviors are emphasized and a mean phonon relaxation time is identified.     

Saving energy in housing

As in many other countries it is only since the energy crisis that methods of house and apartment building in Austria have come under scrutiny in terms of energy conservation. This article, by the director of the Austrian Institute of Building Research, summarises studies carried out by the Institute which led to an energy saving programme that earned a State Prize for research work from the Austrian Ministry of Science.     

Understanding the influence of doping in efficient phosphorescent organic light-emitting diodes with an organic p–i–n homojunction

We report on the development and detailed investigation of highly efficient p–i–n phosphorescent organic light-emitting diodes (PhOLEDs) using 4,4′-bis(carbazol-9-yl)-biphenyl (CBP) as a single organic semiconductor matrix. Following optimization of doping concentration of both the phosphorescent emitter molecule and of the p- and n-type dopants, an external quantum efficiency (EQE) of 15% and a power efficiency (PE) of 28 lm/W are realized at a luminance of 1000 cd/m². These values are comparable to the state-of-the-art for conventional complex multilayered PhOLEDs. By analyzing the device characteristics (i.e. electroluminescence spectra, the current density–voltage behavior of single carrier devices, the transient electroluminescent decay, and the impedance spectroscopy response), we find that the device performance is closely linked to the charge carrier balance in the device, which in turn is governed by the interplay of the conductivities of the doped layers and the transport of each charge carrier species within the emitting layer.     

Understanding the Holocaust through The U.S. Holocaust Memorial Museum

The opening of the United States Holocaust Memorial Museum attracted significant attention in both the popular and the architectural press. This attention and the continuing large numbers of visitors to the Holocaust Museum raise significant questions involving both the paradoxes inherent in the museum as a building type and the particular difficulties in creating a museum specific to the Holocaust. This article addresses a single question: How do visitors come to understand the reality of the Holocaust as they pass through the museum? The focus is primarily on the exhibit sequence, although the building is also discussed. In particular, this article focuses on the question of the “distance” in time and context between the museum's visitors and those who were participants in the Holocaust. I argue that the psychological phenomenon described as “identification” is critical in overcoming this distance in the Holocaust Museum experience.     

Expanding the Horizon of Mechanochromic Detection by Luminescent Shear Stress Sensor Supraparticles

Novel sensor particles have been developed that expand the variety of today's mechanochromic systems. The developed supraparticles consist of several different components to enable the sensor function. First, a luminescence‐quenching core material is coated with silica nanoparticles. Second, this structure is surrounded by raspberry‐like nanostructured silica particles, which host luminophore moieties. Upon shear stress, components spatially separated in the original supraparticles, namely quencher and luminophore components, come into contact. This causes an irreversible quenching of the luminescence (sensor turn‐off). Different options to select core, quencher, and luminophore components allow to drive the sensors to different sensing options regarding response time, sensitivity, and operation time. The sensors can be sensitive and rapid in response or generated to monitor the influence of shear stress over longer periods of time. Thus, a rapid, visible, “on‐the‐fly” sensing of shear stress is possible as well as monitoring the impact of prolonged shear stress. The particles are assembled by spray‐drying. This affords flexibility when choosing the type of quencher and luminophore moiety. As such, the sensitivity of this robust, particle‐based shear stress sensor system can be deliberately configured. Furthermore, the supraparticle sensor can be integrated in surfaces to create interactive, communicating materials.     

CoMP clustering and backhaul limitations in cooperative cellular mobile access networks

Coordinated Multi-Point (CoMP) transmission and reception is a promising solution for managing interference and increasing performance in future wireless cellular systems. Due to its strict requirements in terms of capacity, latency, and synchronization among cooperating Base Stations (BSs), its successful deployment depends on the capability of the mobile backhaul network infrastructure.We deal with the feasibility of CoMP transmission/reception, in particular of Joint Transmission (JT). For this, we first evaluate which cluster sizes are reasonable from the wireless point-of-view to achieve the desired performance gains. Thereafter, we analyze how different backhaul topologies (e.g., mesh and tree structures) and backhaul network technologies (e.g., layer-2 switching and single-copy multicast capabilities) can support these desired clusters. We study for different traffic scenarios and backhaul connectivity levels, which part of the desired BS clusters are actually feasible according to the backhaul characteristics. We found out that a significant mismatch exists between the desired and feasible clusters. Neglecting this mismatch causes overheads in real JT implementations, which complicates or even prevents their deployment.Based on our findings, we propose a clustering system architecture that not only includes wireless information, as done in the state of the art, but also combines wireless and backhaul network feasibility information in a smart way. This avoids unnecessary signaling and User Equipment (UE) data exchange among BSs which are not eligible to take part in the cooperative cluster. Evaluations show that our scheme reduces the signaling and UE data exchange overhead by up to 85% compared to conventional clustering approaches, which do not take into account the backhaul network’s status.