Superradiant Emission from Coherent Excitons in van Der Waals Heterostructures

Recent advancements in isolation and stacking of layered van der Waals materials have created an unprecedented paradigm for demonstrating varieties of 2D quantum materials. Rationally designed van der Waals heterostructures composed of monolayer transition-metal dichalcogenides (TMDs) and few-layer hBN show several unique optoelectronic features driven by correlations. However, entangled superradiant excitonic species in such systems have not been observed before. In this report, it is demonstrated that strong suppression of phonon population at low temperature results in a formation of a coherent excitonic-dipoles ensemble in the heterostructure, and the collective oscillation of those dipoles stimulates a robust phase synchronized ultra-narrow band superradiant emission even at extremely low pumping intensity. Such emitters are in high demand for a multitude of applications, including fundamental research on many-body correlations and other state-of-the-art technologies. This timely demonstration paves the way for further exploration of ultralow-threshold quantum-emitting devices with unmatched design freedom and spectral tunability.     

Decision rules for selecting effect sizes in meta-analysis: A review and reanalysis of psychotherapy outcome studies.

This study deals with some of the judgmental factors involved in selecting effect sizes from within the studies that enter a meta-analysis. Particular attention is paid to the conceptual redundancy rule that Smith, Glass, and Miller (1980) used in their study of the effectiveness of psychotherapy for deciding which effect sizes should and should not be counted in determining an overall effect size. Data from a random sample of 25 studies from Smith et al.'s (1980) population of psychotherapy outcome studies were first recoded and then reanalyzed meta-analytically. Using the conceptual redundancy rule, three coders independently coded effect sizes and identified more than twice as many of them per study as did Smith et al. Moreover, the treatment effect estimates associated with this larger sample of effects ranged between .30 and .50, about half the size claimed by Smith et al. Analyses of other rules for selecting effect sizes showed that average effect estimates also varied with these rules. Such results indicate that the average effect estimates derived from meta-analyses may depend heavily on judgmental factors that enter into how effect sizes are selected within each of the individual studies considered relevant to a meta-analysis. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

"Learning myopia: An adaptive recency effect in category learning": Correction to Jones and Sieck (2003).

Reports an error in "Learning myopia: An adaptive recency effect in category learning" by Matt Jones and Winston R. Sieck (Journal of Experimental Psychology: Learning, Memory, and Cognition, 2003[Jul], Vol 29[4], 626-640). On page 633, Table 2, the values in columns (T, P) and (P, T) in the dual condition row incorrectly read .10 and .90, respectively. The correct values are .90 and .10, respectively. (The following abstract of the original article appeared in record 2003-06626-013.) Recency effects (REs) have been well established in memory and probability learning paradigms but have received little attention in category learning research. Extant categorization models predict REs to be unaffected by learning, whereas a functional interpretation of REs, suggested by results in other domains, predicts that people are able to learn sequential dependencies and incorporate this information into their responses. These contrasting predictions were tested in 2 experiments involving a classification task in which outcome sequences were autocorrelated. Experiment 1 showed that reliance on recent outcomes adapts to the structure of the task, in contrast to models' predictions. Experiment 2 provided constraints on how sequential information is learned and suggested possible extensions to current models to account for this learning. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Top tips for a successful freelance career

The freelance market has grown considerably in recent years,here are ten top tips on writing an effective freelance CV andhow to maximise your chances during an interview.     

Adolescent egocentrism and formal operations: Tests of a theoretical assumption.

The theoretical relation between adolescent egocentrism and formal operations was addressed in 2 studies. In Study 1, this relation was assessed with the Adolescent Egocentrism Scale (AES; R. Enright et al, see PA, Vols 63:5127 and 65:10218) and a battery of formal reasoning tasks administered to 183 6th-, 8th-, 10th-, and 12th-graders. The results reveal only significant negative or nonsignificant correlations between the measures in early adolescence. There was also no evidence of significant developmental covariation from early to middle adolescence. The validation effort was extended in Study 2 to include 2 measures of adolescent egocentrism (AES and the Imaginary Audience Scale [IAS; D. Elkind and R. Bowen, see PA, Vol 62:5769]) and a 2nd battery of formal operations problems. These measures were administered to 117 7th-, 9th-, and 11th-graders and to 56 undergraduates. There was once again no evidence of significant developmental covariation among the measures. The correlations between the AES and IAS were modest, reflecting differences in the nature and content of the measures. It is concluded that little support exists in this study or in the literature for the crucial theoretical assumption of adolescent egocentrism. (19 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The variability of urinary cotinine levels in young children: implications for measuring ETS exposure.

This study examined the within-subject variability of urinary cotinine levels in young children (aged = 0.6-7.2 years) of smoking parents to determine the number of urine samples needed to provide accurate estimates of exposure to environmental tobacco smoke (ETS) for different time intervals. Secondary analyses were conducted of five independent studies (N = 376), in which multiple urinary cotinine measures had been collected over time periods up to 13 months. Over measurement periods of 4-15 days, the within-subject cotinine levels varied 3-5 times more than would be expected based on measurement error alone. Over 7-13 months, the within-subject variability was 10-20 times higher than would be expected based on the measurement error. Findings indicated that cotinine measures from single urine samples provided highly accurate estimates of only recent exposure (i.e., 2-3 days; rho = 0.99). To achieve similarly precise estimates of the mean cotinine level of an individual child over 4-15 days, up to nine urine samples may be necessary. Up to 12 urine samples may be required to achieve similarly precise estimates of ETS exposure over a 4- to 13-month period. Epidemiologic and clinical research on ETS exposure in children can benefit from multiple urine samples (a) to accurately measure average exposure at the level of the individual child, (b) to describe temporal patterns, (c) to detect incidences of peak exposure that would remain underrecognized if monitoring is limited to a single time point, and (d) to establish stable baseline levels and endpoints based on urine samples collected over clinically relevant time periods.     

As Hangs the Flexible Line: Equilibrium of Masonry Arches

In 1675, English scientist Robert Hooke discovered “the true... ...manner of arches for building,” which he summarized with a single phrase: “As hangs the flexible line, so but inverted will stand the rigid arch.” In the centuries that followed, Hooke’s simple idea has been used to understand and design numerous important works. Recent research at MIT on the interactive analysis of structural forces provides new graphical tools for the understanding of arch behavior, which are useful for relating the forces and geometry of masonry structures. The key mathematical principle is the use of graphical analysis to determine possible equilibrium states.     

An implementation of drive key cellular manufacturing

The drive key is one of the most important high-precision components of aircraft braking systems. In this paper, a cost effective drive keys manufacturing process is developed. This proposed manufacturing process makes use of near-net-shape manufacturing, computer numerical control (CNC) machining, and cellular manufacturing methods. To make the proposed process a reality, proper engineering with the proposed parts along with group technology are applied to the product design in conjunction with the proposed manufacturing methods. In addition, a general spreadsheet program is developed for each style of fixture modules to assist in part program coding. Moreover, statistical process control (SPC) is implemented to verify product quality and accept the product at the point of manufacture. It is observed that the implementation of the proposed drive key cellular manufacturing process results in a tremendous improvement in quality, throughput and productivity as well as a drastic reduction in manufacturing operations, workholding fixtures, cutting tools, and inspection media.