High In-content InGaN layers synthesized by plasma-assisted molecular-beam epitaxy: growth conditions, strain relaxation and In incorporation kinetics

We report the interplay between In incorporation and strain relaxation kinetics in high-In-content InxGa1-xN (x = 0.3) layers grown by plasma-assisted molecular-beam epitaxy. For In mole fractions x = 0.13-0.48, best structural and morphological quality is obtained under In excess conditions, at In accumulation limit, and at a growth temperature where InGaN decomposition is active. Under such conditions, in situ and ex situ analysis of the evolution of the crystalline structure with the growth thickness points to an onset of misfit relaxation after the growth of 40 nm, and a gradual relaxation during more than 200 nm which results in an inhomogeneous strain distribution along the growth axis. This process is associated with a compositional pulling effect, i.e. indium incorporation is partially inhibited in presence of compressive strain, resulting in a compositional gradient with increasing In mole fraction towards the surface

"Help Me Help the AI": Understanding How Explainability Can Support Human-AI Interaction

Despite the proliferation of explainable AI (XAI) methods, little is understood about end-users' explainability needs. This gap is critical, because end-users may have needs that XAI methods should but don't yet support. To address this gap and contribute to understanding how explainability can support human-AI interaction, we conducted a study of a real-world AI application via interviews with 20 end-users of Merlin, a bird-identification app. We found that people express a need for practically useful information that can improve their collaboration with the AI system, and intend to use XAI explanations for calibrating trust, improving their task skills, changing their behavior to supply better inputs to the AI system, and giving constructive feedback to developers. We also assessed end-users' perceptions of existing XAI approaches, finding that they prefer part-based explanations. Finally, we discuss implications of our findings and provide recommendations for future designs of XAI, specifically XAI for human-AI collaboration

Collaborative Agency in Youth Online and Offline Creative Production in Scratch

Few studies have focused on how youth develop agency to organize and participate in online unstructured creative collaborations. This paper describes and analyzes how youth programmers organized collaborative groups in response to a programming “Collab Challenge” in the Scratch Online Community and in an accompanying workshop with high school students. The analyses focused on modalities of online collaborations, determined the breadth of online participation, and examined local teens’ awareness of the online community. The discussion addresses youth’s collaborative agency in these new networked contexts, studied the role that online social awareness plays in completing tasks and makes recommendations for the support of online programming communities

Lecturas útiles y entretenidas

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Ensemble of one-class classifiers for personal risk detection based on wearable sensor data

This study introduces the One-Class K-means with Randomly-projected features Algorithm (OCKRA). OCKRA is an ensemble of one-class classifiers built over multiple projections of a dataset according to random feature subsets. Algorithms found in the literature spread over a wide range of applications where ensembles of one-class classifiers have been satisfactorily applied; however, none is oriented to the area under our study: personal risk detection. OCKRA has been designed with the aim of improving the detection performance in the problem posed by the Personal RIsk DEtection(PRIDE) dataset. PRIDE was built based on 23 test subjects, where the data for each user were captured using a set of sensors embedded in a wearable band. The performance of OCKRA was compared against support vector machine and three versions of the Parzen window classifier. On average, experimental results show that OCKRA outperformed the other classifiers for at least 0.53% of the area under the curve (AUC). In addition, OCKRA achieved an AUC above 90% for more than 57% of the users

Internal quantum efficiency of III-nitride quantum dot superlattices grown by plasma-assisted molecular-beam epitaxy

We present a study of the optical properties of GaN/AlN and InGaN/GaN quantum dot (QD) superlattices grown via plasma-assisted molecular-beam epitaxy, as compared to their quantum well (QW) counterparts. The three-dimensional/two-dimensional nature of the structures has been verified using atomic force microscopy and transmission electron microscopy. The QD superlattices present higher internal quantum efficiency as compared to the respective QWs as a result of the three-dimensional carrier localization in the islands. In the QW samples, photoluminescence (PL) measurements point out a certain degree of carrier localization due to structural defects or thickness fluctuations, which is more pronounced in InGaN/GaN QWs due to alloy inhomogeneity. In the case of the QD stacks, carrier localization on potential fluctuations with a spatial extension smaller than the QD size is observed only for the InGaN QD-sample with the highest In content (peak emission around 2.76 eV). These results confirm the efficiency of the QD three-dimensional confinement in circumventing the potential fluctuations related to structural defects or alloy inhomogeneity. PL excitation measurements demonstrate efficient carrier transfer from the wetting layer to the QDs in the GaN/AlN system, even for low QD densities (~1010 cm-3). In the case of InGaN/GaN QDs, transport losses in the GaN barriers cannot be discarded, but an upper limit to these losses of 15% is deduced from PL measurements as a function of the excitation wavelength

ATF4 couples MYC-dependent translational activity to bioenergetic demands during tumour progression.

The c-Myc oncogene drives malignant progression and induces robust anabolic and proliferative programmes leading to intrinsic stress. The mechanisms enabling adaptation to MYC-induced stress are not fully understood. Here we reveal an essential role for activating transcription factor 4 (ATF4) in survival following MYC activation. MYC upregulates ATF4 by activating general control nonderepressible 2 (GCN2) kinase through uncharged transfer RNAs. Subsequently, ATF4 co-occupies promoter regions of over 30 MYC-target genes, primarily those regulating amino acid and protein synthesis, including eukaryotic translation initiation factor 4E-binding protein 1 (4E-BP1), a negative regulator of translation. 4E-BP1 relieves MYC-induced proteotoxic stress and is essential to balance protein synthesis. 4E-BP1 activity is negatively regulated by mammalian target of rapamycin complex 1 (mTORC1)-dependent phosphorylation and inhibition of mTORC1 signalling rescues ATF4-deficient cells from MYC-induced endoplasmic reticulum stress. Acute deletion of ATF4 significantly delays MYC-driven tumour progression and increases survival in mouse models. Our results establish ATF4 as a cellular rheostat of MYC activity, which ensures that enhanced translation rates are compatible with survival and tumour progression

Comedias sueltas del Museo Nacional del Teatro

Copia digital. Madrid : Ministerio de Cultura. Subdirección General de Coordinación Bibliotecaria, 2009Precede al tít. "n.35"Pie de imprenta tomado del colofónSign.:A-C4,D2Texto a dos columna