Learning to Imagine

For the purpose of this discussion, we posit that there are essentially four overarching reasons we educate. They are: preparing students for democratic participation, providing access to knowledge and critical thinking, enabling all students to take advantage of life's opportunities, and enabling students to lead rich and rewarding personal lives. None of these can be achieved fully without attention to the role of imagination. While we acknowledge that not all would agree with our definition of purposes, our comprehensive vision, we believe, can serve our children and our society well

State Complexity of Reversals of Deterministic Finite Automata with Output

We investigate the worst-case state complexity of reversals of deterministic finite automata with output (DFAOs). In these automata, each state is assigned some output value, rather than simply being labelled final or non-final. This directly generalizes the well-studied problem of determining the worst-case state complexity of reversals of ordinary deterministic finite automata. If a DFAO has $n$ states and $k$ possible output values, there is a known upper bound of $k^n$ for the state complexity of reversal. We show this bound can be reached with a ternary input alphabet. We conjecture it cannot be reached with a binary input alphabet except when $k = 2$, and give a lower bound for the case $3 \le k < n$. We prove that the state complexity of reversal depends solely on the transition monoid of the DFAO and the mapping that assigns output values to states.Comment: 18 pages, 3 tables. Added missing affiliation/funding informatio

Employer Demand for Welfare Recipients by Race

This paper uses new survey data on employers in four large metropolitan areas to examine the determinants of employer demand for welfare recipients. The results suggest a high level of demand for welfare recipients, though such demand appears fairly sensitive to business cycle conditions. A broad range of factors, including skill needs and industry, affect the prospective demand for welfare recipients among employers, while other characteristics that affect the relative supply of welfare recipients to these employers (such as location and employer use of local agencies or welfare-to-work programs) influence the extent to which such demand is realized in actual hiring. Moreover, the conditional demand for black (and to a lesser extent Hispanic) welfare recipients lags behind their representation in the welfare population and seems to be more heavily affected by employers’ location and indicators of preferences than by their skill needs or overall hiring activity. Thus, a variety of factors on the demand side of the labor market continue to limit the employment options of welfare recipients, especially those who are minorities.

Local differences in time and extent of mass mortality in Blackbirds ("Turdus merula" L.) after emergence of Usutu virus (USUV; Flaviviridae) in Vienna, Austria

Das Usutu Virus ( = USUV; Flaviviridae), vorher nur in Afrika nachgewiesen, wo es keine fatalen Auswirkungen auf Vögel oder Säugetiere hatte, verursachte erstmals im Sommer 2001 in Wien und Umgebung ein dramatisches Amselsterben. Andere Vogelarten schienen nicht vergleichbar betroffen zu sein. Als Überträger fungieren wahrscheinlich Stechmücken (Culicidae). Die Epidemie erreichte im Sommer 2003 einen Höhepunkt, anschließend entwickelte sich Immunität: Der Anteil Usutu-positiver Totfunde ging rasch zurück, zunehmend viele lebende Vögel besitzen seither Usutu-spezifische Antikörper im Blutserum. Dank unserer vor und nach dem Ereignis erhobenen Amseldichten können wir die Verluste von Teilpopulationen quantitativ belegen und nachweisen, dass es darin in Ausmaß und Zeitraum auffallend kleinräumige Unterschiede gibt. Die Zählungen wurden von den Autoren unabhängig und mit verschiedenen Methoden durchgeführt: Steiner erhob ab 1993 mittels 324 Transektzählungen (TZ) von Sept bis Juni in vier ökologisch z.T. verschiedenen Probeflächen innerhalb des Wiener Siedlungsgebietes am linken Donauufer 1993-97 und 2002-07 relative Vogeldichten (Tab.1). Holzer zählte in den Wintern 2000/01 und 2003/04 Vögel innerhalb von 41 Innenhöfen (IHZ) in zwei Flächen (eine überlappte gering mit einer von Steiner untersuchten, die zweite lag auf der anderen Donauseite), wobei eine praktisch vollständige Erfassung der Amseln möglich war (Abb.1 und 2). Die Ergebnisse bezüglich des Winterbestandes decken sich weitestgehend: Die Amseldichten waren zwischen 85 und 89% (TZ Mühlschüttel, Tab.4) bzw. 88% (IHZ, Abb.1) zurückgegangen. Für die Erhebung der Brutbestände liegen nur Zahlen aus TZ vor, als methodisch günstigster Zeitraum wurde dafür der April gewählt; Tab.5 gibt relative Abundanzen (Amseln je 1.000 m Transektlänge) an, Tab.6 Ergebnisse von Signifikanztests. In den vier Flächen war die Brutzeitdichte im gleichen Verhältnis zurückgegangen wie die im Winter (Tab.3 und 5). Aus dem für die Art am wenigsten geeigneten Teilgebiet Donaufeld liegt zwischen 2004 und 06 keine Amselfeststellung vor (Tab.1); Aussagen von zwei interessierten Familien, die am Transekt Futterstellen betreiben, erhärten diesen Befund. Erste Vögel zeigten sich dort erst wieder 2007. Auch die geringen Restbestände der übrigen drei Flächen konnten sich bis 2007 nicht erholen. Anders verlief die Entwicklung in Kaisermühlen, das nur 2,0-2,6 km von den anderen Donau-nahen Flächen entfernt liegt. Hier wurde 1998/99 und ab 2002 gezählt (35 TZ): Der Aprilbestand war 2002 um ein Drittel zurückgegangen, 2005 weniger drastisch als in den anderen Flächen eingebrochen und bereits 2006 wieder in alter Dichte vorhanden (Tab.2 und 5). Noch weniger stark wurden die Amseln der sechsten TZFläche (Wiener Innenstadt 70 TZ) betroffen, die Aprildichte war dort erst 2004 etwa auf die Hälfte reduziert und hatte sich zwei Jahre später wieder erholt (Tab.2 und 5). In beiden Fällen ging der Bestand zur Brutzeit erst zumindest ein Jahr nach Zusammenbruch des Winterbestandes zurück (Tab.3). Aus unseren Befunden lässt sich schließen, dass sich vier der untersuchten Amsel-Teilpopulationen als isolierte Standvögel verhielten, da ein winterlicher Zuzug dort praktisch nicht stattfand (in allen Monaten gleichmäßiger Rückgang) und zwischen nahe liegenden Flächen kein wesentlicher Austausch zur Auffüllung der Bestände erfolgte. Die Amseldichte dieser Flächen verblieb zumindest bis 2007 trotz der ab 2004 in Ostösterreich zunehmenden Immunität gegen USUV auf extrem niederem Niveau. Möglicherweise reduzierten überstandene USUV-Infektionen die Fitness überlebender Vögel und setzten solcherart deren Fortpflanzungerfolg herab. – Für die Bestände der restlichen beiden Gebiete hat dies offenbar geringere oder keine Bedeutung. Wenn in anderen Teilen Mitteleuropas in den Sommermonaten Totfunde von Amseln gehäuft auftreten, sollten diese mit genauer Fundortangabe versehen unverzüglich Virologen übermittelt oder bis dahin tiefgekühlt zwischengelagert werden.USUV, previously known from Africa only, never before had been associated with fatal disease in vertebrates. Beginning with summer 2001, it caused mass mortality from mid-July to September in Blackbirds of Vienna and surroundings. From 2003 to 05 herd immunity developed and the proportion of USUV-positive dead Blackbirds decreased. As we have counted urban birds before and after summer 2001, we analysed population decrease of the species quantitatively. We used different methods: Steiner counted birds from September to June in established transects in six urban areas, beginning with 1993. Holzer in two districts recorded absolute numbers of birds in courts completely enclosed by buildings, in winters 2000/01 and 2003/04 respectively. For transect-counts density in January and February was considered to be typical for winter, in April for breeding time. To an unexpected scale, we found differences between subpopulations in time and extent of mortality: In six of the eight areas, with nearest distances from 0,2 to 2,9 km to river Danube, results are identical, regardless of method. In all months and subpopulations in 2002 decrease was between 58 and 94%, in one area after 2002 the species disappeared completely for four years, as late as 2007 two birds had been found again. As decrease in all months was very similar (Tab.4) it can be concluded, that the birds are strictly resident. Four of these subpopulations investigated at breeding time also, were unable for six years to increase their very low densities – in spite of herd immunity developing in Vienna after 2003. Reduced fitness of surviving individuals could explain this phenomenon. In remaining two areas, one being situated close to river Danube and to the six cited above, decrease was recorded (1) first in winter, in April in later years only, (2) decrease was not as dramatically, (3) increase to original densities occurred within one or two years. As USUV meanwhile emerged in Hungary, northern Italy and Switzerland, in case of mass mortality in summer, it is recommended to store dead birds in frozen condition or to bring it to a veterinary institution immediately

Green's Relations in Finite Transformation Semigroups

We consider the complexity of Green's relations when the semigroup is given by transformations on a finite set. Green's relations can be defined by reachability in the (right/left/two-sided) Cayley graph. The equivalence classes then correspond to the strongly connected components. It is not difficult to show that, in the worst case, the number of equivalence classes is in the same order of magnitude as the number of elements. Another important parameter is the maximal length of a chain of components. Our main contribution is an exponential lower bound for this parameter. There is a simple construction for an arbitrary set of generators. However, the proof for constant alphabet is rather involved. Our results also apply to automata and their syntactic semigroups.Comment: Full version of a paper submitted to CSR 2017 on 2016-12-1

Are Suburban Firms More Likely to Discriminate Against African Americans?

This paper presents a test of the hypothesis that employers in suburban locations are more likely to discriminate against African Americans than are employers located in central cities. Using a difference-in-difference framework, we compare central-city/suburban differences in racial hiring outcomes for firms where a white person is in charge of hiring (white employers, for short) to similar geographic differences in outcomes for firms where a black person is in charge of hiring (black employers). We find that both suburban black and white employers hire fewer blacks than their central-city counterparts. Moreover, the central-city/suburban hiring gap among black employers is as large as, or larger than, that of white employers. Suburban black employers, however, receive many more applications from blacks and hire more blacks than do white firms in either location.

Within Cities and Suburbs: Racial Residential Concentration and the Spatial Distribution of Employment Opportunities across Submetropolitan Areas

In this paper, we examine and compare the spatial distributions of jobs and people across submetropolitan areas using data on firms from the Multi-City Study of Urban Inequality and data on people from the U.S. Bureau of the Census. The results indicate that less-educated people and those on public assistance mostly reside in areas with high minority populations. Low-skill jobs are quite scarce in these areas, while the availability of such jobs relative to less-educated people in heavily white suburban areas is high. Large fractions of the low-skill jobs in these metropolitan areas are not accessible by public transit. Furthermore, there is significant variation within both central cities and suburbs in the ethnic composition of residents and in the availability of low-skill jobs. The ability of various minority groups to gain employment in each area depends heavily on the ethnic composition of the particular area.