Friction Variability in Planar Pushing Data: Anisotropic Friction and Data-collection Bias

Friction plays a key role in manipulating objects. Most of what we do with our hands, and most of what robots do with their grippers, is based on the ability to control frictional forces. This paper aims to better understand the variability and predictability of planar friction. In particular, we focus on the analysis of a recent dataset on planar pushing by Yu et al. [1] devised to create a data-driven footprint of planar friction. We show in this paper how we can explain a significant fraction of the observed unconventional phenomena, e.g., stochasticity and multi-modality, by combining the effects of material non-homogeneity, anisotropy of friction and biases due to data collection dynamics, hinting that the variability is explainable but inevitable in practice. We introduce an anisotropic friction model and conduct simulation experiments comparing with more standard isotropic friction models. The anisotropic friction between object and supporting surface results in convergence of initial condition during the automated data collection. Numerical results confirm that the anisotropic friction model explains the bias in the dataset and the apparent stochasticity in the outcome of a push. The fact that the data collection process itself can originate biases in the collected datasets, resulting in deterioration of trained models, calls attention to the data collection dynamics.Comment: 8 pages, 13 figure

Does Foreign Aid Help Reduce Income Inequality?

The aim of this paper is to provide empirical evidence on the link between foreign aid and income inequality for the period 1973-2002. Since simple cross-country regressions cannot be taken as `true` time series findings, we also focus on dynamic panel data techniques, which allow accounting for potential simultaneity and heterogeneity problems. We do not find very robust evidence that foreign aid is conducive to the improvement of the distribution of income, even when the quality of institutions is taken into account. This finding is consistent with recent empirical research on aid and growth that shows that such a link is weak at best.

K-median: exact recovery in the extended stochastic ball model

We study exact recovery conditions for the linear programming relaxation of the k-median problem in the stochastic ball model (SBM). In Awasthi et al. (2015), the authors give a tight result for the k-median LP in the SBM, saying that exact recovery can be achieved as long as the balls are pairwise disjoint. We give a counterexample to their result, thereby showing that the k-median LP is not tight in low dimension. Instead, we give a near optimal result showing that the k-median LP in the SBM is tight in high dimension. We also show that, if the probability measure satisfies some concentration assumptions, then the k-median LP in the SBM is tight in every dimension. Furthermore, we propose a new model of data called extended stochastic ball model (ESBM), which significantly generalizes the well-known SBM. We then show that exact recovery can still be achieved in the ESBM.Comment: Accepted by Mathematical Programming Series

Serovar distribution of a DNA sequence involved in the antigenic relationship between Leptospira and equine cornea

BACKGROUND: Horses infected with Leptospira present several clinical disorders, one of them being recurrent uveitis. A common endpoint of equine recurrent uveitis is blindness. Serovar pomona has often been incriminated, although others have also been reported. An antigenic relationship between this bacterium and equine cornea has been described in previous studies. A leptospiral DNA fragment that encodes cross-reacting epitopes was previously cloned and expressed in Escherichia coli. RESULTS: A region of that DNA fragment was subcloned and sequenced. Samples of leptospiral DNA from several sources were analysed by PCR with two primer pairs designed to amplify that region. Reference strains from serovars canicola, icterohaemorrhagiae, pomona, pyrogenes, wolffi, bataviae, sentot, hebdomadis and hardjo rendered products of the expected sizes with both pairs of primers. The specific DNA region was also amplified from isolates from Argentina belonging to serogroups Canicola and Pomona. Both L. biflexa serovar patoc and L. borgpetersenii serovar tarassovi rendered a negative result. CONCLUSIONS: The DNA sequence related to the antigen mimicry with equine cornea was not exclusively found in serovar pomona as it was also detected in several strains of Leptospira belonging to different serovars. The results obtained with L. biflexa serovar patoc strain Patoc I and L. borgpetersenii serovar tarassovi strain Perepelicin suggest that this sequence is not present in these strains, which belong to different genomospecies than those which gave positive results. This is an interesting finding since L. biflexa comprises nonpathogenic strains and serovar tarassovi has not been associated clinically with equine uveitis

A Preschool Aged Obesity Prevention Project Designed to Increase Moderate to Vigorous Physical Activity

Purpose: The purpose of Juntos Y Saludables (Get Healthy Together [GHT]) is to reduce the prevalence of childhood obesity by focusing on physical activity and healthy eating. GHT is an ongoing project, with phase one of three completed in May 2010.The GHT program was implemented in the Edgewood Independent School District’s Head Start centers located in San Antonio, TX. These centers were selected due to high prevalence of obesity (50%) and diabetes in children and adults living in the community. Method: The gross motor intervention was implemented at two of the three centers. The intervention consisted of teacher training and supplemental gross motor resources (lesson plans and activity resources). The System for Observing Fitness Instruction Time (SOFIT) was used to assess the amount of time spent in moderate to vigorous physical activity (MVPA) and the Learning Accomplishment Profile – 3rd Editions (LAP-3) were used to evaluate the program’s effects on gross motor development. Results: At the start of the project, the two intervention centers were spending eleven minutes (roughly 24%) of their gross motor class period engaged in MVPA while at the end of the program sixteen minutes (roughly 35%) of the time was spent engaged in MVPA. There was an overall increase in physical activity (P\u3c0.001) and MVPA (P\u3c0.019) levels in both intervention and control centers. A similar linear improvement was also observed in the LAP-3 results. At the conclusion of the project, all of the students either met or were above their gross motor developmental ages. Conclusion: Through the implementation of the GHT Gross Motor intervention a significant increase occurred in the student’s gross motor skills and the percentage of time spent in MVPA

The Local Nanohertz Gravitational-Wave Landscape From Supermassive Black Hole Binaries

Supermassive black hole binaries (SMBHBs) in the 10 million to 10 billion $M_\odot$ range form in galaxy mergers, and live in galactic nuclei with large and poorly constrained concentrations of gas and stars. There are currently no observations of merging SMBHBs--- it is in fact possible that they stall at their final parsec of separation and never merge. While LIGO has detected high frequency GWs, SMBHBs emit GWs in the nanohertz to millihertz band. This is inaccessible to ground-based interferometers, but possible with Pulsar Timing Arrays (PTAs). Using data from local galaxies in the 2 Micron All-Sky Survey, together with galaxy merger rates from Illustris, we find that there are on average $91\pm7$ sources emitting GWs in the PTA band, and $7\pm2$ binaries which will never merge. Local unresolved SMBHBs can contribute to GW background anisotropy at a level of $\sim20\%$, and if the GW background can be successfully isolated, GWs from at least one local SMBHB can be detected in 10 years.Comment: submitted to Nature Astronomy (reformatted for arXiv