Reduced dimensionality in layered quantum dimer magnets: Frustration vs. inhomogeneous condensates

Motivated by recent experiments on BaCuSi2O6, we investigate magnetic excitations and quantum phase transitions of layered dimer magnets with inter-layer frustration. We consider two scenarios, (A) a lattice with one dimer per unit cell and perfect inter-layer frustration, and (B) an enlarged unit cell with inequivalent layers, with and without perfect frustration. In all situations, the critical behavior at asymptotically low temperatures is three-dimensional, but the corresponding crossover scale may be tiny. Magnetic ordering in case (B) can be discussed in terms of two condensates; remarkably, perfect frustration renders the proximity effect ineffective. Then, the ordering transition will be generically split, with clear signatures in measurable properties. Using a generalized bond-operator method, we calculate the low-temperature magnetic properties in the paramagnetic and antiferromagnetic phases. Based on the available experimental data on BaCuSi2O6, we propose that scenario (B) with inequivalent layers and imperfect frustration is realized in this material, likely with an additional modulation of the inter-layer couling along the c axis.Comment: 23 pages, 18 figs, (v2) new fig for bandwidths, (v3) triplon binding energy discussed, (v4) small changes for clarification, accepted (PRB

Die Bedeutung von Merkmalen des Individuums und Merkmalen der Lernumgebung für die Akzeptanz von E-Learning in Unternehmen

Due to the increasing need for training, more and more companies employ new communication and information technologies in the context of e-learning for further education. However, many firms are confronted with a lack of acceptance of e-learning at the workplace, which is mirrored in insufficient usage (see Venkatesh & Davis, 2000). This study tries to examine the influence of both the learner’s characteristics and the characteristics of the learning-environment on the acceptance of e-learning. Acceptance models which focus attitudinal and behavioral aspects are the background of this study (see Davis, 1989). Acceptance thus includes attitudes towards the usage of new technologies and the behavior itself. However, the models rarely offer any clues referring to the influence of context factors. This study focuses on the impact of aspects of the learner and aspects of the learning-environment on attitudinal and behavioral acceptance. Cognitive as well as motivational factors are examined as indicators for the learner’s characteristics. As indicators for the learning environment the didactical and the medial design are examined. The results show a direct relation of some examined factors on attitudinal acceptance and an indirect relation on usage (behavioral acceptance). This outcome suggests a special consideration of these aspects to foster acceptance of e-learning at the workplace.Aufgrund des erhöhten Bildungsbedarfs gehen immer mehr Unternehmen dazu über, die neuen Kommunikations- und Informationstechnologien im Sinne von E-Learning für die Weiterbildung zu nutzen. Allerdings sind viele Unternehmen mit einer mangelnden Akzeptanz von E-Learning konfrontiert, die sich in einer unzureichenden Nutzung widerspiegelt (vgl. Venkatesh & Davis, 2000). Diese Studie versucht Faktoren zu identifizieren, die einen Einfluss auf die Akzeptanz von E-Learning von Seiten der Mitarbeiter ausüben. Theoretischen Hintergrund dieser Studie bilden Akzeptanzmodelle (vgl. Davis, 1989), die auf einen Einstellungs- und Verhaltensaspekt fokussieren. Akzeptanz beinhaltet somit die Einstellung gegenüber der Nutzung der neuen Technologien und das Verhalten selbst. Die vorliegende Studie fokussiert auf den Einfluss von Merkmalen des Individuums und Merkmalen der Lernumgebung auf die Einstellungs- und Verhaltensakzeptanz. Es werden kognitive und emotional-motivationale Faktoren als Indikatoren für die Merkmale des Individuums und die didaktische und mediale Gestaltung als Indikator für die Merkmale der Lernumgebung betrachtet. Die Ergebnisse bestätigten einen direkten Zusammenhang der untersuchten Faktoren auf die Einstellungsakzeptanz und einen indirekten auf die Nutzung (Verhaltensakzeptanz). Diese Befunde sprechen für eine besondere Beachtung dieser Aspekte zur Akzeptanzförderung

Superconducting d-wave stripes in cuprates: Valence bond order coexisting with nodal quasiparticles

We point out that unidirectional bond-centered charge-density-wave states in cuprates involve electronic order in both s- and d-wave channels, with non-local Coulomb repulsion suppressing the s-wave component. The resulting bond-charge-density wave, coexisting with superconductivity, is compatible with recent photoemission and tunneling data and as well as neutron-scattering measurements, once long-range order is destroyed by slow fluctuations or glassy disorder. In particular, the real-space structure of d-wave stripes is consistent with the scanning-tunneling-microscopy measurements on both underdoped Bi2Sr2CaCu2O8+x and Ca2-xNaxCuO2Cl2 of Kohsaka et al. [Science 315, 1380 (2007), arXiv:cond-mat/0703309].Comment: 5 pages, 3 figs, (v2) final version to be published in PR

Assessing the convergent validity between the automated emotion recognition software Noldus FaceReader 7 and Facial Action Coding System Scoring

This study validates automated emotion and action unit (AU) coding applying FaceReader 7 to a dataset of standardized facial expressions of six basic emotions (Standardized and Motivated Facial Expressions of Emotion). Percentages of correctly and falsely classified expressions are reported. The validity of coding AUs is provided by correlations between the automated analysis and manual Facial Action Coding System (FACS) scoring for 20 AUs. On average 80% of the emotional facial expressions are correctly classified. The overall validity of coding AUs is moderate with the highest validity indicators for AUs 1, 5, 9, 17 and 27. These results are compared to the performance of FaceReader 6 in previous research, with our results yielding comparable validity coefficients. Practical implications and limitations of the automated method are discussed

User experience and clinical effectiveness with two wearable global positioning system devices in home dementia care

Introduction: The user experience and clinical effectiveness with wearable global positioning system (GPS) devices for persons with dementia (PwDs) and caregivers (CGs) remain unclear although many are available. Methods: Using a crossover design, 20 dyads tested two similar commercial GPS watches (products A and B) at home for 4 weeks each. Usability, product functions, design features and product satisfaction at home and the clinic were investigated. Caregiver burden and quality of life assessed clinical effectiveness. Results: The final 17 dyads rated the usability, telephone function, overall design features, font, buttons, and battery life of B significantly better than A. PwDs rated the overall design features and buttons of A significantly better than CGs. Product satisfaction with both products was significantly lower at home. Clinical effectiveness was not found. Discussion: User experience can be improved by optimizing specific product details. This might translate to clinical effectiveness. Social desirability bias may explain different product satisfaction ratings

A 183 GHz metamorphic HEMT low-noise amplifier with 3.5 dB noise figure

This paper presents a 183 GHz low-noise amplifier (LNA), designed primarly for water vapor detection in atmosphere. The LNA requirements were defined by MetOp Second Generation (MetOp-SG) Microwave Sounder, Microwave Imager and Ice Cloud Imager instruments. MetOp-SG is the European contribution to operational meteorological observations from polar orbit. This LNA advances the current state-of-the-art for the InGaAs metamorphic high electron mobility transistor (mHEMT) technology. The five-stage common-source MMIC amplifier utilizes transistors with a gate length of 50 nm. On-wafer measurements show a noise figure of 3.5 dB at the operative frequency, about 1 dB lower than previously reported mHEMT LNAs, and a gain of 24±2 dB over the bandwidth 160-200 GHz. The input and output matching are -11 dB and -10 dB, respectively. Moreover, the DC power dissipation at the optimal bias for noise is as low as 24 mW

Low noise amplifiers for MetOp-SG

We present low-noise amplifiers (LNA) that have been developed in the framework of two pre-qualification ESA projects for frequencies between 54 and 229 GHz for the METOP-SG satellite program. The main goal of these satellites is water vapor detection in atmospheric science and weather forecasting which advances the current state of the art for the metamorphic high electron mobility transistor (mHEMT) technology. The MMIC amplifiers are based on the In0.52Al0.48As/In0.8Ga0.2As/In0.53Ga0.47As heterostructure and utilize transistors with a gate length of 50 nm. On-wafer measurements will be presented for all frequency bands as well as results of packaged LNAs

Treatment characteristics and outcomes of pure Acinar cell carcinoma of the pancreas - A multicentric European study on radically resected patients

Background: Acinar cell carcinomas (ACC) belong to the exocrine pancreatic malignancies. Due to their rarity, there is no consensus regarding treatment strategies for resectable ACC. Methods: This is a retrospective multicentric study of radically resected pure pancreatic ACC. Primary endpoints were overall survival (OS) and disease-free survival (DFS). Further endpoints were oncologic outcomes related to tumor stage and therapeutic protocols. Results: 59 patients (44 men) with a median age of 64 years were included. The median tumor size was 45.0 mm. 61.0% were pT3 (n = 36), nodal positivity rate was 37.3% (n = 22), and synchronous distant metastases were present in 10.1% of the patients (n = 6). 5-Years OS was 60.9% and median DFS 30 months. 24 out of 31 recurred systemically (n = 18 only systemic, n = 6 local and systemic). Regarding TNM-staging, only the N2-stage negatively influenced OS and DFS (p = 0.004, p = 0.001). Adjuvant treatment protocols (performed in 62.7%) did neither improve OS (p = 0.542) nor DFS (p = 0.159). In 9 cases, radical resection was achieved following neoadjuvant therapy. Discussion: Radical surgery is currently the mainstay for resectable ACC, even for limited metastatic disease. Novel (neo)adjuvant treatment strategies are needed, since current systemic therapies do not result in a clear survival benefit in the perioperative setting