Undulatory swimming in fluids with polymer networks

The motility behavior of the nematode Caenorhabditis elegans in polymeric solutions of varying concentrations is systematically investigated in experiments using tracking and velocimetry methods. As the polymer concentration is increased, the solution undergoes a transition from the semi-dilute to the concentrated regime, where these rod-like polymers entangle, align, and form networks. Remarkably, we find an enhancement in the nematode's swimming speed of approximately 65% in concentrated solutions compared to semi-dilute solutions. Using velocimetry methods, we show that the undulatory swimming motion of the nematode induces an anisotropic mechanical response in the fluid. This anisotropy, which arises from the fluid micro-structure, is responsible for the observed increase in swimming speed.Comment: Published 1 November 2013 in Europhysics Letter

A Demographic and Economic Profile of Duluth, Minnesota, and Superior, Wisconsin

In this brief, authors Andrew Schaefer, Marybeth Mattingly, and Douglas Gagnon present a demographic and economic profile of Duluth, Minnesota, and Superior, Wisconsin, with a specific focus on families with children. Analyzing data from the American Community Survey and U.S. Decennial Census on family income and poverty, they compare—wherever possible—conditions in Duluth and Superior to those in Minnesota, Wisconsin, and the nation as a whole. They report that, in both Duluth and Superior, poverty among families with children has increased substantially in the last 15 years; by 2010 and 2015, family poverty was higher in each city than across the nation or statewide. In St. Louis County, Minnesota—home of Duluth—low income families have experienced declines in their income over the past 40 years, while income has grown for more well-off families

State EITC Programs Provide Important Relief to Families in Need

In this brief, authors Douglas Gagnon, Marybeth Mattingly, and Andrew Schaefer discuss the estimated effects of state Earned Income Tax Credit (EITC) benefits on rates of poverty in 2010–2014 using the Current Population Survey Annual Social and Economic Supplement. They report that, on average, individuals in states with refundable state EITCs receive a 17.6 percent match of their federal EITC benefit, and the state supplement pulls an estimated 0.3 percent of these states’ combined populations out of poverty. Children receive the greatest benefit, as state EITCs reduce child poverty by 0.7 percentage point overall. Even those who remain poor after receiving state EITC benefits get a sizeable boost: on average these families receive $455, which amounts to 2.4 percent of their total family earnings. The authors also examined state EITC receipt by family characteristics, finding larger average benefits for metropolitan and non-white- and Hispanic-headed households. Arizona, Arkansas, Georgia, Nevada, and Texas would experience the greatest estimated reductions in child poverty rates if they were to adopt a state EITC

Federal EITC Kept 2 Percent of the Population Out of Poverty Greatest Poverty Reductions in Texas, North Carolina, and Arizona

This brief documents the proportion of Americans who would have been poor absent the Earned Income Tax Credit (EITC), all else being equal, across 2010–2014. It consists of a pooled sample using the Current Population Survey (CPS) Annual Social and Economic Supplement (ASEC) between the years of 2011–2015. Authors Douglas Gagnon, Marybeth Mattingly, and Andrew Schaefer examine Supplemental Poverty Measure (SPM) rates as well as hypothetical increases in the rates of poverty in the absence of federal EITC benefits. They report that the proportion of people who are poor in the United States as measured by the SPM would increase by two percentage points without EITC dollars. In addition, children are especially at risk of becoming poor without EITC benefits, as 1 out of every 25 would become poor without the EITC. The authors also highlight variability across states, noting that the federal EITC led to the greatest poverty reductions in the states of Texas, North Carolina, and Arizona

Group classification of (1+1)-Dimensional Schr\"odinger Equations with Potentials and Power Nonlinearities

We perform the complete group classification in the class of nonlinear Schr\"odinger equations of the form $i\psi_t+\psi_{xx}+|\psi|^\gamma\psi+V(t,x)\psi=0$ where $V$ is an arbitrary complex-valued potential depending on $t$ and $x,$ $\gamma$ is a real non-zero constant. We construct all the possible inequivalent potentials for which these equations have non-trivial Lie symmetries using a combination of algebraic and compatibility methods. The proposed approach can be applied to solving group classification problems for a number of important classes of differential equations arising in mathematical physics.Comment: 10 page

Etnički sukob kao unutar-grupna pojava: preliminarni okvir

The literature on "ethnic conflict" tends to focus solely on external sources of such conflict. But this unquestioning focus on ethnic conflict as due to factors in the relationship between "ethnic groups" or their elites may at times be misleading. Drawing on a critique of conflict theory as developed in the field of international relations, I point out the conceptual and methodological problems associated with the analysis of inter-group conflict, and point to the importance of within-group conflict, especially conflict between elites, as sources of external conflict. I apply this critique to the concept of ethnic conflict and point out the consequences of such questioning for understanding the causes of violent conflict along ethnic lines.U literaturi posvećenoj etničkim sukobima postoji tendencija da se u obzir uzmu samo izvanjski izvori sukoba. Takvo stajalište - da su glavni uzroci etničkih sukoba u karakteru odnosa među etničkim skupinama, odnosno njihovim elitama - može, međutim, biti pogrešno. U radu se izlaže kritika konfliktne teorije razrađene unutar znanstvenog (politologijskoga) područja međunarodnih odnosa. Kritika obuhvaća koncepcijske i metodološke probleme analize među-grupnih sukoba i ukazuje na važnost unutar-grupnih sukoba (sukoba među "domaćim" elitama) kao izvora onih prvih. U zaključku, autor ističe važnost izložene kritike za razumijevanje uzroka i izvora nasilnih sukoba koji slijede etničke markere