A simple theory for the dependence of the electrical resistance of the magnetic superconductors TmRh4B4 and ErRh4B4 on temperature and field

The warmup rate of the¹⁶⁵Ho-enhanced nuclear spins in a HoVO₄ single crystal in contact with dilute³He is shown to be dominated by the Kapitza resistanceR _K at low bath temperature (T _b <100 mK). This result is obtained from an analysis of the NMR signal during the warmup, following a demagnetization which cools the sample to a temperature of about 5 mK. The temperature variation ofR _K (T _b< ^/–3 ) is consistent with the acoustic mismatch model, but the magnitude is 40 times smaller than the theoretical predictions for a solid-liquid interface. The spin-lattice relaxation is also estimated, and found to be in agreement with the results of other authors.     

Contradictory relationship between Hurst parameter and queueing performance (extended version)

Long Range Dependent (LRD) network traffic does not behave like the traffic generated by the Poisson model or other Markovian models. From the network performance point of view, the main difference is that LRD traffic increases queueing delays due to its burstiness over many time scales. LRD behavior has been observed in different types and sizes of networks, for different applications (e.g., WWW) and different traffic aggregations. Since LRD behaviour is not rare nor isolated, accurate characterization of LRD traffic is very important in order to predict performance and to allocate network resources. The Hurst parameter is commonly used to quantify the degree of LRD and the burstiness of the traffic. In this paper we investigate the validity and effectiveness of the Hurst parameter. To this end, we analyze the UCLA Computer Science Department network traffic traces and compute their Hurst parameters. Queueing simulation is used to study the impact of LRD and to determine if the Hurst parameter accurately describes such LRD. Our results show that the Hurst parameter is not by itself an accurate predictor of the queueing performance for a given LRD traffic trace.     

Low‐cost upscaling compatibility of five different ITO‐free architectures for polymer solar cells

Five different indium‐tin‐oxide free (ITO‐free) polymer solar cell architectures provided by four participating research institutions that all presented a laboratory cell performance sufficient for use in mobile and information and communication technology (ICT) were evaluated based on photovoltaic performance and lifetime tests according to the ISOS protocols. The comparison of the different device architectures was performed using the same active material (P3HT: PCBM) and tested against an ITO‐based reference device. The active area was 1 cm² and rigid glass or flexible polyester substrates were employed. The performance results were corroborated by use of a round robin methodology between the four participating laboratories (DTU/DK, ECN/NL, Frauenhofer ISE/DE, and the Holst Centre/NL), while the lifetime testing experiments were carried out in only one location (DTU). Five different lifetime testing experiments were carried out for a minimum of 1000 h: (1) shelf life (according to ISOS‐D‐1); (2–3) stability under continuous 1 sun illumination (1000 Wm^?2, AM1.5G) at low (37 ± 3°C) and high (80 ± 5°C) temperatures (according to ISOS‐L‐1 and ISOS‐L‐2); (4) stability under continuous low‐light conditions at 0.1 sun (100 Wm^?2, AM1.5G, 32°C) (according to ISOS‐LL); (5) continuous illumination (670 Wm^?2, AM1.5G) at high temperature (65°C) and high humidity (50% RH) (according to ISOS‐L‐3). Finally, the upscaling compatibility of these device architectures based on the device photovoltaic behavior, stability and scalability were identified and we confirm that an architecture that presents a high score in only one aspect of the solar cell performance is not sufficient to justify an investment in upscaling. Many will require further technical development. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 944‐954, 2013     

Asymmetric TiO2 hybrid photocatalytic ceramic membrane with porosity gradient: Effect of structure directing agent on the resulting membranes architecture and performances

Asymmetric TiO₂ hybrid photocatalytic ceramic membranes with porosity gradient have been fabricated via acid-catalyzed sol–gel method. Different structure directing agents (SDAs) i.e. Pluronic P-123, Triton X-100, Tween 20 and Tween 80 were incorporated in the preparation of TiO₂ sol to obtain a porous multilayered TiO₂ coated on the alumina ceramic support. Six different SDA-modified membrane specimens were fabricated. Four of which were coated with the TiO₂ sols prepared using only one type of SDA. The remaining two specimens were fabricated via multilayer coating of different TiO₂ sols prepared using different types of SDAs. Physico-chemical and morphological properties of different TiO₂ layers were thoroughly investigated. The membrane M1 which had the most porous TiO₂ sub-layers showed a high pure water permeability of 155 L m⁻² h⁻¹ bar⁻¹. The membrane showed a relatively high Rhodamine B (RhB) removal of 2997 mg m⁻² over 8 h treatment duration in the batch photoreactor, second only to the Pluronic-based TiO₂ membrane (specific RhB removal of 3050 mg m⁻²). All membrane specimens exhibited good performances while operated in the flow-through photocatalytic membrane reactor. Over 91% of RhB removal capability was retained after 4 treatment cycles. All membranes also showed self-cleaning property by retaining >90% of initial flux after 4 treatment cycles. The flexibility of optimizing membrane performances by fine-tuning the porosity gradient configuration of the photocatalytic layer has also been demonstrated.     

How students structure and relate argumentative knowledge when learning together with diagrams

When students learn together by discussing a topic, they sometimes are asked to construct an argumentative diagram. An argumentative diagram consists of boxes with arguments and arrows that relate these boxes. Constructing argumentative diagrams can be especially useful for structuring and relating argumentative knowledge. However, students do not always seem to use a diagram’s structure and relations to their benefit. To focus on structure and relations, 46 secondary school students were asked to either label the boxes in a diagram with argumentative labels such as ‘argument in favor’ and ‘rebuttal’, or to label the arrows with more causal labels such as ‘but’, and ‘because’. The students discussed two topics in dyads using a computer environment with chat and diagram. Then a post-test was given to assess their opinion and arguments. We found no difference between conditions in the extent to which students broadened and deepened their discussion. However, students who labeled the arrows contrasted subtopics more. The students who contrasted subtopics more showed better results on the post-test. Instruction and diagram design can thus influence students’ discussion, although the general results also show us that students need more instruction and reflection to optimally benefit from argumentative diagrams.     

Degradation mechanisms in organic photovoltaic devices

In the present review, the main degradation mechanisms occurring in the different layer stacking (i.e. photoactive layer, electrode, encapsulation film, interconnection) of polymeric organic solar cells and modules are discussed. Bulk and interfacial, as well as chemical and physical degradation mechanisms are reviewed, as well as their implications and external or internal triggers. Decay in I-V curves in function of time is usually due to the combined action of sequential and interrelated mechanisms taking place at different locations of the device, at specific kinetics. This often makes the identification of specific root causes of degradation challenging in non-model systems. Additionally, constant development and refinement in terms of type and combination of materials and processes render the ranking of degradation mechanisms as a function of their probability of occurrence and their detection challenging.However, it clearly appears that for the overall stability of organic photovoltaic devices, the actual photoactive layer, as well as the properties of the barrier and substrate (e.g. cut of moisture and oxygen ingress, mechanical integrity), remain critical. Interfacial stability is also crucial, as a modest degradation at the level of an interface can quickly and significantly influence the overall device properties.     

Multigigabit multiplexer design

Describes a time division multiplexer design for multiGbit/s operation. The design is based on a delay line travelling-pulse concept using dual-gate GaAs MESFETs. The function of the multiplexer is verified by both implementation of a 4:1 multiplexer device and by mwSPICE simulations