Greedy learning of latent tree models for multidimensional clustering

Machine Learning - Real-world data are often multifaceted and can be meaningfully clustered in more than one way. There is a growing interest in obtaining multiple partitions of data. In previous...     

Plasma-plasmonics synergy in the Ga-catalyzed growth of Si-nanowires

This paper reports on the growth of Si nanowires (NWs) by SiH₄/H₂ plasmas using the non-noble Ga-nanoparticles (NPs) catalysts. A comparative investigation of conventional Si-NWs vapour–liquid–solid (VLS) growth catalyzed by Au NPs is also reported. We investigate the use of a hydrogen plasma and of a SiH₄/H₂ plasma for removing Ga oxide shell and for enhancing the Si dissolution into the catalyst, respectively. By exploiting the Ga NPs surface plasmon resonance (SPR) sensitivity to their surface chemistry, the SPR characteristic of Ga NPs has been monitored by real time spectroscopic ellipsometry in order to control the hydrogen plasma/Ga NPs interaction and the involved processes (oxide removal and NPs dissolution by volatile gallium hydride). Using in situ laser reflectance interferometry the metal catalyzed Si NWs growth process has been investigated to find the effect of the plasma activation on the growth kinetics. The role of atomic hydrogen in the NWs growth mechanism and, in particular, in the SiH₄ dissolution into the catalysts, is discussed. We show that while Au catalysts because of the re-aggregation of NPs yields NWs that do not correspond to the original size of the Au NPs catalyst, the NWs grown by the Ga catalyst retains the diameter dictated by the size of the Ga NPs. Therefore, the advantage of Ga NPs as catalysts for controlling NWs diameter is demonstrated.     

How Has Body Image Changed? A Cross-Sectional Investigation of College Women and Men From 1983 to 2001.

Body-image dissatisfaction is not uncommon and can adversely affect individuals' psychosocial functioning and quality of life. Various oft-cited surveys and a meta-analysis implicate a worsening of body image over the past several decades, especially among women and possibly among men. The present cross-sectional study examined changes in multiple facets of body image among 3,127 college students from 1983 through 2001; the same standardized assessment was used in 22 studies conducted within the same university. Results confirmed non-Black women's increasing body-image dissatisfaction until the early or mid-1990s, after which significant improvements occurred in terms of overall body-image evaluation and overweight preoccupation among both non-Black and Black women, despite heavier body weights. A reduction over time in women's investment in their appearance was also evident. Men's body image was relatively stable during the 19-year period. Explanations, limitations, and implications of the findings are discussed. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

REquirements TRacing On target (RETRO): improving software maintenance through traceability recovery

A number of important tasks in software maintenance require an up-to-date requirements traceability matrix (RTM): change impact analysis, determination of test cases to execute for regression testing, etc. The generation and maintenance of RTMs are tedious and error-prone, and they are hence often not done. In this paper, we present REquirements TRacing On-target (RETRO), a special- purpose requirements tracing tool. We discuss how RETRO automates the generation of RTMs and present the results of a study comparing manual RTM generation to RTM generation using RETRO. The study showed that RETRO found significantly more correct links than manual tracing and took only one third of the time to do so. Work performed while A. Dekhtyar was on the faculty at the University of Kentucky.     

Interactionism, flexibility, and inferences about the past.

Addresses key issues raised by the nine preceding commentators (see records 1999-05337-005, 1999-05337-006, 1999-05337-007, 1999-05337-008, 1999-05337-009, 1999-05337-010, 1999-05337-011, 1999-05337-012, and 1999-05337-013) on the present authors' article Adaptations, Exaptations, and Spandrels (see record 1998-01669-001). (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Exploring environments by hand or foot: Time-based heuristics for encoding distance in movement space.

In Experiment 1, blindfolded observers judged (a) the distance of pathways felt by hand and (b) the straight-line distance between pathway endpoints inferred from such exploration. In Experiment 2, blindfolded observers made corresponding estimates after traversing similar pathways on foot. Pathways were explored under three different speeds. Under both manipulatory and ambulatory exploration, there was substantial length distortion of inferred distance; the straight-line distance was increasingly overestimated with increases in the length of the explored pathway. With manipulatory exploration, slower movements increased length distortion, but duration effects proved secondary to effects of spatial extent. For ambulatory exploration, no duration effects were obtained. Observers used time-independent heuristics, that is, a footstep metric for estimating the pathway actually travelled and a spatial imaging strategy for estimating the inferred line between pathway endpoints. The studies establish length distortion as a general phenomenon in movement space and identify its major causes as spatial rather than temporal. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Modification of 4H-SiC and 6H-SiC(0001)<Subscript>Si</Subscript> surfaces through the interaction with atomic hydrogen and nitrogen

The interaction of 4H-SiC(0001)_Si and 6H-SiC(0001)_Si surfaces with atomic hydrogen and atomic nitrogen produced by remote radio-frequency plasmas is investigated. The kinetics of the surface modifications is monitored in real time using ellipsometry, while chemical modifications of the surface are characterized using x-ray photoelectron spectroscopy (XPS). Film morphological properties are assessed with atomic force microscopy (AFM). A two-stage substrate preparation procedure is described that effectively removes oxygen from the SiC surface at low (200°C) temperature. In the first step, the SiC surface is etched with an HCl/HF acid solution as an alternative to the conventional HF(1%)-H₂O solution. The HCl/HF etch provides effective hydrogen passivation of the SiC surface. In the second step, the SiC surface is exposed to atomic hydrogen that selectively interacts with residual oxygen. In addition, the temperature dependence of the nitridation of SiC surfaces has also been investigated. It is found that interaction of SiC surfaces with atomic hydrogen at 200°C provides clean, smooth, and terraced surfaces suitable for epitaxial growth. In contrast, SiC surface exposure at high temperature (750°C) to atomic hydrogen and nitrogen results in very rough and disordered Si-rich surfaces. Finally, we find that the 4H-SiC surface is more reactive than the 6H-SiC surface to both species studied, independent of temperature. Surface geometry and electronic factors responsible for the observed reactivities are discussed.     

KINETICS OF AQUEOUS ETHYLENEDIAMINE-ETHANOL-ANTHRAQUINONE DELIGNIFICATION PROCESS

A new organosolv pulping method has been investigated. Delignification can be carried out by digesting the lignocellulosic material in an aqueous solution of ethylenediamine (EDA) and ethanol (EtOH) in combination with catalytic amounts of anthraquinone (AQ). This aqueous EDA-EtOH-AQ pulping is found to be highly selective in delignification and is flexible to softwoods. Bulk delignification was found to take place according to a pair of first-order mechanisms, like aqueous ethanol pulping. In the initial phase of delignification more than 50% lignin is removed, while the rest is extracted in the second slower step. The rate constants for each step are of the same order of magnitude and higher than those obtained in ethanol pulping. This indicated that overall delignification is faster when compared to aqueous ethanol pulping. The Arrhenius activation energy for the initial step was found to be 6.4 kcal/mole. The high selectivity in the detignification during the EDA-EtOH—AQ process is observed at all levels of delignification and shows at least an 18—20% increase in yield when compared with ethanol pulping.     

Emotional reactivity to daily events in major and minor depression.

Although emotional dysfunction is an important aspect of major depressive disorder (MDD), it has rarely been studied in daily life. Peeters, Nicolson, Berkhof, Delespaul, and deVries (2003) observed a surprising mood-brightening effect when individuals with MDD reported greater reactivity to positive events. To better understand this phenomenon, we conducted a multimethod assessment of emotional reactivity to daily life events, obtaining detailed reports of appraisals and event characteristics using the experience-sampling method and the Day Reconstruction Method (Kahneman, Krueger, Schkade, Schwarz, & Stone, 2004) in 35 individuals currently experiencing a major depressive episode, 26 in a minor depressive (mD) episode, and 38 never-depressed healthy controls. Relative to healthy controls, both mood-disordered groups reported greater daily negative affect and lower positive affect and reported events as less pleasant, more unpleasant, and more stressful. Importantly, MDD and mD individuals reported greater reductions in negative affect following positive events, an effect that converged across assessment methods and was not explained by differences in prevailing affect, event appraisals, or medications. Implications of this curious mood-brightening effect are discussed. (PsycINFO Database Record (c) 2010 APA, all rights reserved)