Are We Wasting Our Children's Time by Giving Them More Homework?

Following an identification strategy that allows us to largely eliminate unobserved student and teacher traits, we examine the effect of homework on math, science, English and history test scores for eighth grade students in the United States. Noting that failure to control for these effects yields selection biases on the estimated effect of homework, we find that math homework has a large and statistically meaningful effect on math test scores throughout our sample. However, additional homework in science, English and history are shown to have little to no impact on their respective test scores.first differencing, unobserved traits, instrumental variable, selection bias, homework

Are we wasting our children's time by giving them more homework?

Following an identification strategy that allows us to largely eliminate unobserved student and teacher traits, we examine the effect of homework on math, science, English and history test scores for eighth grade students in the United States. Noting that failure to control for these effects yields selection biases on the estimated effect of homework, we find that math homework has a large and statistically meaningful effect on math test scores throughout our sample. However, additional homework in science, English and history are shown to have little to no impact on their respective test scores

The effect of teacher gender on student achievement in primary school: Evidence from a randomized experiment

This paper attempts to reconcile the contradictory results found in the economics literature and the educational psychology literature with respect to the academic impact of gender dynamics in the classroom. Specifically, using data from a randomized experiment, we look at the effects of having a female teacher on the math test scores of students in primary school. We find that female students who were assigned to a female teacher without a strong math background suffered from lower math test scores at the end of the academic year. This negative effect however not only seems to disappear but it becomes (marginally) positive for female students who were assigned to a female teacher with a strong math background. Finally, we do not find any effect of having a female teacher on male students' test scores (math or reading) or female students' reading test scores. Taken together, our results tentatively suggest that the findings in these two streams of the literature are in fact consistent if one takes into account a teacher's academic background in math

Peer Effects in Disadvantaged Primary Schools: Evidence from a Randomized Experiment

We examine the effect of peer achievement on students' own achievement and teacher performance in primary schools in disadvantaged neighborhoods using data from a well-executed randomized experiment in seven states. Contrary to the existing literature, we find that the average classroom peer achievement adversely influences own student achievement in math and reading in linear-in-means models. Extending our analysis to take into account the potential non-linearity in the peer effects leads to non-negligible differences along the achievement distribution. We test several models of peer effects to further understand their underlying mechanisms. While we find no evidence to support the monotonicity model and little evidence in favor of the ability grouping model, we find stronger evidence to support the frame of reference and the invidious comparison models. Moreover, we also find that higher achieving classes improve teaching performance in math. Finally, using a simple policy experiment we find suggestive evidence that tracking students by ability potentially benefits students who end up in a low achievement class while hurting students in a high achievement class

Simultaneous ipsilateral proximal interphalangeal and metacarpophalangeal dislocation of the fifth phalanx: A case report

We propose, analyze and demonstrate the optoelectronic phase-locking of optical waves whose frequencies are chirped continuously and rapidly with time. The optical waves are derived from a common optoelectronic swept-frequency laser based on a semiconductor laser in a negative feedback loop, with a precisely linear frequency chirp of 400 GHz in 2 ms. In contrast to monochromatic waves, a differential delay between two linearly chirped optical waves results in a mutual frequency difference, and an acoustooptic frequency shifter is therefore used to phase-lock the two waves. We demonstrate and characterize homodyne and heterodyne optical phase-locked loops with rapidly chirped waves, and show the ability to precisely control the phase of the chirped optical waveform using a digital electronic oscillator. A loop bandwidth of ∼ 60 kHz, and a residual phase error variance of < 0.01 rad^2 between the chirped waves is obtained. Further, we demonstrate the simultaneous phase-locking of two optical paths to a common master waveform, and the ability to electronically control the resultant two-element optical phased array. The results of this work enable coherent power combining of high-power fiber amplifiers—where a rapidly chirping seed laser reduces stimulated Brillouin scattering—and electronic beam steering of chirped optical waves

Designing and analyzing park sensor system for efficient and sustainable car park area management

Many problems have been seen in cities because of increasing vehicle density. One of these problems is vehicle density in parking lots. People look for empty parking areas and they spend too much time. While people look for empty parking areas, CO2 (carbon dioxide) emission and energy consumption increase due to density in parking lots. We worked to solve these problems by doing Magnetic Car Park Sensor. Magnetic Car Park Sensor is the system which detects cars in car parks. After cars detected with the system, the system sends information to center server and we can see information data in the system interface. The system helps people to find empty parking lots. As people find empty car park areas fastly, energy consumption and CO2 emission are decreased significantly

The fluctuating resource hypothesis explains invasibility, but not exotic advantage following disturbance

Invasibility is a key indicator of community susceptibility to changes in structure and function. The fluctuating resource hypothesis (FRH) postulates that invasibility is an emergent community property, a manifestation of multiple processes that cannot be reliably predicted by individual community attributes like diversity or productivity. Yet, research has emphasized the role of these individual attributes, with the expectation that diversity should deter invasibility and productivity enhance it. In an effort to explore how these and other factors may influence invasibility, we evaluated the relationship between invasibility and species richness, productivity, resource availability, and resilience in experiments crossing disturbance with exotic seed addition in 1-m2 plots replicated over large expanses of grasslands in Montana, USA and La Pampa, Argentina. Disturbance increased invasibility as predicted by FRH, but grasslands were more invasible in Montana than La Pampa whether disturbed or not, despite Montana´s higher species richness and lower productivity. Moreover, invasibility correlated positively with nitrogen availability and negatively with native plant cover. These patterns suggested that resource availability and the ability of the community to recover from disturbance (resilience) better predicted invasibility than either species richness or productivity, consistent with predictions from FRH. However, in ambient, unseeded plots in Montana, disturbance reduced native cover by >50% while increasing exotic cover >200%. This provenance bias could not be explained by FRH, which predicts that colonization processes act on species? traits independent of origins. The high invasibility of Montana grasslands following disturbance was associated with a strong shift from perennial to annual species, as predicted by succession theory. However, this shift was driven primarily by exotic annuals, which were more strongly represented than perennials in local exotic vs. native species pools. We attribute this provenance bias to extrinsic biogeographic factors such as disparate evolutionary histories and/or introduction filters selecting for traits that favor exotics following disturbance. Our results suggest that (1) invasibility is an emergent property best explained by a community´s efficiency in utilizing resources, as predicted by FRH but (2) understanding provenance biases in biological invasions requires moving beyond FRH to incorporate extrinsic biogeographic factors that may favor exotics in community assembly.Fil: Pearson, Dean. United State Forest Service; Estados Unidos. University of Montana; Estados UnidosFil: Ortega, Yvette K.. United State Forest Service; Estados UnidosFil: Villarreal, Diego. Universidad Nacional de La Pampa. Facultad de Ciencias Exactas y Naturales; ArgentinaFil: Lekberg, Ylva. University of Montana; Estados UnidosFil: Cock, Marina Cecilia. Consejo Nacional de Investigaciones Científicas y Técnicas. Instituto de Ciencias de la Tierra y Ambientales de La Pampa. Universidad Nacional de La Pampa. Facultad de Ciencias Exactas y Naturales. Instituto de Ciencias de la Tierra y Ambientales de La Pampa; ArgentinaFil: Eren, Ozkan. Adnan Menderes Universitesi; TurquíaFil: Hierro, Jose Luis. Consejo Nacional de Investigaciones Científicas y Técnicas. Instituto de Ciencias de la Tierra y Ambientales de La Pampa. Universidad Nacional de La Pampa. Facultad de Ciencias Exactas y Naturales. Instituto de Ciencias de la Tierra y Ambientales de La Pampa; Argentin

In-plane quasi-static compression deformation of Ti6Al4V double arrow-headed lattice structures fabricated by electron beam powder bed fusion process: Build orientation, scan speed and failure mechanism

Eren Z., Gokcekaya O., Nakano T., et al. In-plane quasi-static compression deformation of Ti6Al4V double arrow-headed lattice structures fabricated by electron beam powder bed fusion process: Build orientation, scan speed and failure mechanism. Journal of Materials Research and Technology 27, 6192 (2023); https://doi.org/10.1016/j.jmrt.2023.11.027.The 2D double arrow-headed (DAH) lattice structures, which are promising cellular structures for impact mitigation, remain relatively unexplored in terms of their compression response when manufactured using the powder bed fusion process with Ti6Al4V (Ti64) alloy. This study aims to investigate the effects of build orientation and beam scan speed of Electron Beam Powder Bed Fusion (PBF-EB) process on the energy absorption of 2D Ti64 DAH lattice structures. Additionally, potential microstructural variations due to adjusted process parameters can be linked to different levels of energy absorption. For the compressions, the lattice structures were manufactured at two build orientations (0° and 45°), using three different beam scan speeds: speed function (SF), low speed (LS), high speed (HS). In micro-characterizations, the unit cells of 0deg-LS exhibited the lowest micro-porosity level at 0.12 %. Based on KAM values, thin struts at unit cells had higher residual stresses than thick struts, contributing to the initiation of failure locations. The compressions revealed that the 0deg-LS group absorbed 21.6 % and 24 % more energy than 0deg-SF and 0deg-HS groups, respectively, at compressions of 33 %. 45° samples absorbed approximately 10 % more energy than 0° samples except HS groups. The lowest micro-porosity of 0deg-LS contributed to having the highest energy absorption among 0deg samples. As the residual stresses in KAM values did not differ strongly with varying beam speed, varied energy absorptions were not linked to them. An optimization of the numerical compressions helped obtain designs with higher energy absorption and less relative volume. This study provides valuable insights into Ti64 cellular applications constrained with 2D-type designs

Comparison of in-plane compression of additively manufactured Ti6Al4V 2D auxetic structures: Lattice design, manufacturing speed, and failure mode

Eren Z., Gokcekaya O., Balkan D., et al. Comparison of in-plane compression of additively manufactured Ti6Al4V 2D auxetic structures: Lattice design, manufacturing speed, and failure mode. Materials and Design 241, 112885 (2024); https://doi.org/10.1016/j.matdes.2024.112885.The metal-based 2D auxetic lattice structures hold the potential for multifunctional tasks in aerospace applications. However, the compression response of those manufactured by powder bed fusion process is underexplored. This study proposes a comprehensive comparison of in-plane quasi-static compression performance of 2D auxetic lattice structures, utilizing three designs (anti-tetrachiral (ATC), double arrow-headed (DAH), and tree-like re-entrant (TLR)), manufactured with stiff Ti6Al4V by the electron beam powder bed fusion process (PBF-EB) with various manufacturing speeds. The results revealed unique failure patterns and superior energy absorptions among 2D lattice structures in the literature. TLR design enhanced energy absorption by overcoming failures between DAH columns and exhibited the lowest standard deviations in specific energy absorption (SEA) values (9.75 %–12.62 %). Besides, Kernel average misorientation (KAM) values followed the order of DAH, TLR, and ATC, and inversely correlated with SEA values. ATC structures with the lowest KAM outperformed DAH and TLR by 47.5 % and 6.44 %, respectively. Scan speed variations affected SEA and porosity values differently for each lattice design while exhibiting similar microstructure characteristics. The findings in this study propose a significant contribution to the development of aerospace sandwich structures where harsh environments exist and employment of 2D topologies are required