Severe Loss Probabilities in Portfolio Credit Risk Models

We derive explicit sharp bounds on the distribution of the number of defaults from a pool of obligors with common probability of default and default correlation. These bounds are extremely wide, implying that default probabilities and default correlations only very loosely determine probabilities of severe portfolio losses. Our results quantify and thereby reinforce Gordy’s (2002) statement that “Capital decisions ... depend on higher moments”.Portfolio Credit Risk Models

Stability of a tethered satellite system

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/76302/1/AIAA-1991-474-527.pd

CONCENTRATION ISSUES IN THE U.S. BEEF SUBSECTOR

Industrial Organization, Livestock Production/Industries,

Neurogenin2 Expression in Ventral and Dorsal Spinal Neural Tube Progenitor Cells Is Regulated by Distinct Enhancers

AbstractThe basic helix-loop-helix transcription factor Neurogenin2 (NGN2) is expressed in distinct populations of neural progenitor cells within the developing central and peripheral nervous systems. Transgenic mice containing ngn2/lacZ reporter constructs were used to study the regulation of ngn2 in the developing spinal cord. ngn2/lacZ transgenic embryos containing sequence found 5′ or 3′ to the ngn2 coding region express lacZ in domains that reflect the spatial and temporal expression profile of endogenous ngn2. A 4.4-kb fragment 5′ of ngn2 was sufficient to drive lacZ expression in the ventral neural tube, whereas a 1.0-kb fragment located 3′ of ngn2 directed expression to both dorsal and ventral domains. Persistent β-gal activity revealed that the NGN2 progenitor cells in the dorsal domain give rise to a subset of interneurons that send their axons to the floor plate, and the NGN2 progenitors in the ventral domain give rise to a subset of motor neurons. We identified a discrete element that is required for the activity of the ngn2 enhancer specifically in the ventral neural tube. Thus, separable regulatory elements that direct ngn2 expression to distinct neural progenitor populations have been defined

The International Implications of Quality-of-Life Policing as Practiced in New York City

The New York City Police Department (NYPD) has made enforcement of laws against disorder and quality-of-life offenses a central part of its policing strategy. Concomitantly, New York City (NYC) experienced a renaissance in orderliness, cleanliness, tourism, real estate value, and crime reduction, although other problems such as poverty, unemployment, drug abuse, racial tensions, and homelessness persist. This paper examines quality-of-life policing practices in NYC, describes the philosophical underpinnings, explores the critical response to the program, and presents lessons of potential relevance to other policing organizations in the USA and around the world

Characterization of Graphs With Failed Skew Zero Forcing Number of 1

Given a graph $G$, the zero forcing number of $G$, $Z(G)$, is the smallest cardinality of any set $S$ of vertices on which repeated applications of the forcing rule results in all vertices being in $S$. The forcing rule is: if a vertex $v$ is in $S$, and exactly one neighbor $u$ of $v$ is not in $S$, then $u$ is added to $S$ in the next iteration. Hence the failed zero forcing number of a graph was defined to be the size of the largest set of vertices which fails to force all vertices in the graph. A similar property called skew zero forcing was defined so that if there is exactly one neighbor $u$ of $v$ is not in $S$, then $u$ is added to $S$ in the next iteration. The difference is that vertices that are not in $S$ can force other vertices. This leads to the failed skew zero forcing number of a graph, which is denoted by $F^{-}(G)$. In this paper we provide a complete characterization of all graphs with $F^{-}(G)=1$. Fetcie, Jacob, and Saavedra showed that the only graphs with a failed zero forcing number of $1$ are either: the union of two isolated vertices; $P_3$; $K_3$; or $K_4$. In this paper we provide a surprising result: changing the forcing rule to a skew-forcing rule results in an infinite number of graphs with $F^{-}(G)=1$.Comment: 8 pages, this research was supported by the National Science Foundation Research forUndergraduates Award 195018

Energy Gradients Structure Microbial Communities Across Sediment Horizons in Deep Marine Sediments of the South China Sea

The deep marine subsurface is a heterogeneous environment in which the assembly of microbial communities is thought to be controlled by a combination of organic matter deposition, electron acceptor availability, and sedimentology. However, the relative importance of these factors in structuring microbial communities in marine sediments remains unclear. The South China Sea (SCS) experiences significant variability in sedimentation across the basin and features discrete changes in sedimentology as a result of episodic deposition of turbidites and volcanic ashes within lithogenic clays and siliceous or calcareous ooze deposits throughout the basin\u27s history. Deep subsurface microbial communities were recently sampled by the International Ocean Discovery Program (IODP) at three locations in the SCS with sedimentation rates of 5, 12, and 20 cm per thousand years. Here, we used Illumina sequencing of the 16S ribosomal RNA gene to characterize deep subsurface microbial communities from distinct sediment types at these sites. Communities across all sites were dominated by several poorly characterized taxa implicated in organic matter degradation, including Atribacteria, Dehalococcoidia, and Aerophobetes. Sulfate-reducing bacteria comprised only 4% of the community across sulfate-bearing sediments from multiple cores and did not change in abundance in sediments from the methanogenic zone at the site with the lowest sedimentation rate. Microbial communities were significantly structured by sediment age and the availability of sulfate as an electron acceptor in pore waters. However, microbial communities demonstrated no partitioning based on the sediment type they inhabited. These results indicate that microbial communities in the SCS are structured by the availability of electron donors and acceptors rather than sedimentological characteristics

The Haematopoietic Stem Cell Niche: New Insights into the Mechanisms Regulating Haematopoietic Stem Cell Behaviour

The concept of the haematopoietic stem cell (HSC) niche was formulated by Schofield in the 1970s, as a region within the bone marrow containing functional cell types that can maintain HSC potency throughout life. Since then, ongoing research has identified numerous cell types and a plethora of signals that not only maintain HSCs, but also dictate their behaviour with respect to homeostatic requirements and exogenous stresses. It has been proposed that there are endosteal and vascular niches within the bone marrow, which are thought to regulate different HSC populations. However, recent data depicts a more complicated picture, with functional crosstalk between cells in these two regions. In this review, recent research into the endosteal/vascular cell types and signals regulating HSC behaviour are considered, together with the possibility of a single subcompartmentalised niche

Long-Distance Movement of a Female Polar Bear from Canada to Russia

Polar bears (Ursus maritimus) display fidelity to large geographic regions, and their movements are influenced by sea ice distribution. Polar bear subpopulations are moderately distinct from one another, and long-distance movements between subpopulations are rare. We describe and analyze the movements of a female polar bear tracked by satellite telemetry from spring 2009 for 798 days. This female traveled an exceptionally long distance (totaling 11 686 km) from the sea ice off the Yukon Territory, Canada (Southern Beaufort Sea subpopulation) to Wrangel Island, Russia (Chukchi Sea subpopulation). In comparison to other polar bears in this study, this bear traveled farther, moved faster, and had a much larger home range in the first year. Furthermore, the calculation of the home range size by two different methods demonstrated that the commonly used minimum convex polygon method overestimated the home range compared to the less biased Brownian bridge movement model. This female’s long-distance movement was unusual and provides additional evidence for gene flow between subpopulations. Monitoring polar bear movements is useful to track such events, which is especially important at present because sea ice loss due to climate change can affect subpopulation boundaries and influence management.L’ours polaire (Ursus maritimus) démontre sa fidélité à de grandes régions géographiques, et ses déplacements subissent l’influence de la répartition de la glace de mer. Les sous-populations d’ours polaires sont modérément distinctes les unes des autres, et les déplacements sur de longues distances entre les sous-populations sont rares. Nous décrivons et analysons les déplacements d’une ourse polaire suivie par télémétrie satellitaire pendant 798 jours à compter du printemps 2009. Cette femelle s’est déplacée sur une distance exceptionnellement longue (11 686 km au total) depuis la glace de mer au large du territoire du Yukon, au Canada (sous-population du sud de la mer de Beaufort) jusqu’à l’île Wrangel, en Russie (sous-population de la mer des Tchouktches). Comparativement à d’autres ours polaires visés par cette étude, cette ourse s’est déplacée plus loin et plus vite, et elle avait un domaine vital beaucoup plus vaste au cours de sa première année. De plus, le calcul de la taille de son domaine vital effectué au moyen de deux méthodes différentes a permis de constater que la méthode fréquemment utilisée du polygone convexe minimum donnait lieu à la surestimation du domaine vital comparativement au modèle de mouvement moins faussé du pont brownien. Le déplacement de cette ourse sur de longues distances était inhabituel et il permet d’obtenir des preuves supplémentaires au sujet du flux génétique entre les sous-populations. La surveillance des déplacements des ours polaires est utile dans le cadre du suivi de tels événements, ce qui est particulièrement important en ce moment, car la perte de glace de mer attribuable au changement climatique peut avoir des effets sur les frontières des sous-populations et la gestion des influences