CMB seen through random Swiss Cheese

We consider a Swiss Cheese model with a random arrangement of LemaitreTolman-Bondi holes in Lambda CDM cheese. We study two kinds of holes with radius r(b) = 50 h(-1) Mpc, with either an underdense or an overdense centre, called the open and closed case, respectively. We calculate the effect of the holes on the temperature, angular diameter distance and, for the first time in Swiss Cheese models, shear of the CMB. We quantify the systematic shift of the mean and the statistical scatter, and calculate the power spectra. In the open case, the temperature power spectrum is three orders of magnitude below the linear ISW spectrum. It is sensitive to the details of the hole, in the closed case the amplitude is two orders of magnitude smaller. In contrast, the power spectra of the distance and shear are more robust, and agree with perturbation theory and previous Swiss Cheese results. We do not find a statistically significant mean shift in the sky average of the angular diameter distance, and obtain the 95% limit vertical bar Delta D-A/(D) over bar (A)vertical bar less than or similar to 10(-4). We consider the argument that areas of spherical surfaces are nearly unaffected by perturbations, which is often invoked in light propagation calculations. The closed case is consistent with this at 1 sigma, whereas in the open case the probability is only 1.4%.Peer reviewe

Average expansion rate and light propagation in a cosmological Tardis spacetime

We construct the first exact statistically homogeneous and isotropic cosmological solution in which inhomogeneity has a significant effect on the expansion rate. The universe is modelled as a Swiss Cheese, with dust FRW background and inhomogeneous holes. We show that if the holes are described by the quasispherical Szekeres solution, their average expansion rate is close to the background under certain rather general conditions. We specialise to spherically symmetric holes and violate one of these conditions. As a result, the average expansion rate at late times grows relative to the background, i.e. backreaction is significant. The holes fit smoothly into the background, but are larger on the inside than a corresponding background domain: we call them Tardis regions. We study light propagation, find the effective equations of state and consider the relation of the spatially averaged expansion rate to the redshift and the angular diameter distance.Peer reviewe

Dinamički potencijal povratnih informacija u samoreguliranom učenju i motivaciji djece s teškoćama u učenju matematike

The present study was designed to examine the effects of feedback conditions on learning and motivation of children identified with mathematical learning difficulties (MLDs). The performance of 76 fifth grade children on computational math skills and related task motivation was assessed. The groups of children were randomly assigned to one of two treatment conditions: immediate corrective feedback or delayed conventional feedback on two occasions. Results showed that children performed significantly better when they were provided with the immediate corrective feedback than when they were provided with the delayed conventional feedback. The findings suggest that provision of the immediate corrective feedback also enhanced task motivation in children. In contrast, provision of the delayed conventional feedback had a negative impact on children’s task motivation and also on their performance in math. Moreover, the results indicated that in the long term, children’s subgroup (MLDs) and their previous math skills were powerful predictors of subsequent performance on a limited-time math task, whereas the change in task motivation did not contribute significantly to the same task.Ovim istraživanjem želio se ispitati učinak vrste povratnih informacija (feedback-a) na učenje i motivaciju djece s teškoćama u učenju matematike. Procijenjena je izvedba 76-ero djece - polaznika petih razreda na zadacima računanja, kao i njihova motivacija za rješavanje matematičkih zadataka, s obzirom na vrstu povratne informacije: trenutnu korektivnu povratnu informaciju te odgođenu konvencionalnu povratnu informaciju. Rezultati istraživanja pokazali su da su djeca imala značajno bolji rezultat kada im je bila pružena trenutna korektivna povratna informacija, nego kada im je pružena odgođena konvencionalna povratna informacija. Rezultati također ukazuju da pružanje trenutne povratne informacije povećava motivaciju učenika za rješavanje zadataka. S druge strane, pružanje odgođene povratne informacije imalo je negativan utjecaj na motivaciju, kao i na izvedbu u rješavanju matematičkih zadataka. Rezultati također pokazuju da su prisutnost matematičkih teškoća i prethodna razina razvoja matematičkih vještina bili značajni prediktori kasnije uspješnosti u rješavanju vremenski ograničenih zadataka, što, međutim, nije bio slučaj s promjenama u motiviranosti učenika

Can a supervoid explain the Cold Spot?

Peer reviewe

FÖR- OCH NACKDELAR MED BILDBEHANDLING FÖR ANALYS AV EFFEKTEN AV EN TRAFIKSÄKERHETSÅTGÄRD

The fact that there are no crashes during every three-year period on every spot of a road network does not mean that the long-term safety level is exactly zero crashes. However, what the lack of recorded crashes does mean is that we need less blunt instruments than crash data for evaluating, for example, the effectiveness of a reconstruction. A new tool, image processing, is presented. It includes reliability tests of an automatic feature for speed measurements and of more detailed semi-automatic features to study the interaction between vulnerable road users and motor vehicle drivers. A case studie from Sweden and Germany is also presented

Plant residue mulch increases measured and modelled soil moisture content in the effective root zone of maize in semi-arid Kenya

Difficulties in efficient utilization of seasonal precipitation cause limitations in yields and even total crop failure on rainfed farms in semi-arid East Africa. The objective of the present study was to find out if covering the soil with plant residue mulch at a semi-arid site could retain water in the soil between precipitation events and build dry spell resilience by reducing soil water evaporation and increasing infiltration to deeper soil. Covering soil with plant residue mulch was studied at a smallholder farm in semi-arid Kenya by continuously measuring volumetric soil moisture content with soil sensors at multiple depths in bare soil and in maize (Zea mays L.) plant residue mulched soil. A physically based one-dimensional soil moisture model was calibrated and used to estimate the effect of plant residue mulch on soil moisture over a two-year period (multiple growing seasons). The modelled multiyear time series provides an estimate of the effect residue mulches of different thicknesses have on soil moisture over time. The simple soil moisture model was able to estimate soil moisture in the effective root zone of maize. By comparing measured data from mulched and uncovered soil and by model prediction, it was demonstrated that maize residue mulch conserved soil moisture over time in the effective root zone of maize compared to bare soil. During the two-year period mulching increased the total amount of days when measured relative soil moisture (s) exceeded water stress limit of maize (s*) by 24%-46%. Moisture accumulated in the mulched profile, especially in the deeper layers of the effective root zone. Calculations indicated that further increasing mulch thickness (delta(m)) from 1 to 3 cm would have increased the total days when s > s* 59%. Furthermore, increasing delta(m) from 3 to 5 cm would have resulted in 25% increase in total days when s > s*. According to our calculations mulching (delta(m) > 1 cm) could have maintained s > s* throughout a 19 days dry spell that occurred during the measurement period. The demonstrated moisture conserving effect of mulch increases with delta(m), but availability of plant residue may set limits on mulch application rates. The results suggest that maize residue mulching is as an accessible and feasible method for conserving soil moisture in the effective root zone in dryland smallholder systems in East Africa.Peer reviewe

Effects of Gender on Basic Numerical and Arithmetic Skills : Pilot Data From Third to Ninth Grade for a Large-Scale Online Dyscalculia Screener

In this study, we analyzed the development and effects of gender on basic number skills from third to ninth grade in Finland. Because the international comparison studies have shown slightly different developmental trends in mathematical attainment for different language groups in Finland, we added the language of education as a variable in our analysis. Participants were 4,265 students from third to ninth grade in Finland, representing students in two national languages (Finnish, n = 2,833, and Swedish, n = 1,432). Confirmatory factor analyses showed that the subtasks in the dyscalculia screener formed two separate factors, namely, number-processing skills and arithmetic fluency. We found a linear development trend across age cohorts in both the factors. Reliability and validity evidence of the measures supported the use of these tasks in the whole age group from 9 to15 years. In this sample, there was an increasing gender difference in favor of girls and Swedish-speaking students by grade levels in number-processing skills. At the same time, boys showed a better performance and a larger variance in tasks measuring arithmetic fluency. The results indicate that the gender ratio within the group with mathematical learning disabilities depends directly on tasks used to measure their basic number skills.Peer reviewe

Scaling in the correlation energies of two-dimensional artificial atoms

We find an unexpected scaling in the correlation energy of artificial atoms, i.e., harmonically confined two-dimensional quantum dots. The scaling relation is found through extensive numerical examinations including Hartree-Fock, variational quantum Monte Carlo, density-functional, and full configuration-interaction calculations. We show that the correlation energy, i.e., the true ground-state total energy subtracted by the Hartree-Fock total energy, follows a simple function of the Coulomb energy, confimenent strength and, the number of electrons. We find an analytic expression for this function, as well as for the correlation energy per particle and for the ratio between the correlation and total energies. Our tests for independent diffusion Monte Carlo and coupled-cluster results for quantum dots -- including open-shell data -- confirm the generality of the obtained scaling. As the scaling is also well applicable to $\gtrsim$ 100 electrons, our results give interesting prospects for the development of correlation functionals within density-functional theory.Comment: Accepted to Journal of Physics: Condensed Matte