An international survey of stress tests

In the summer of 2000, central banks from the Group of Ten countries surveyed large international banks about their use of stress tests_a risk management tool that measures a firm's exposure to extreme movements in asset prices. The survey findings highlight the risks that most concern financial institutions and clarify how these institutions use stress tests in their overall risk management programs.Risk management ; Risk assessment ; Financial services industry

Overcoming Memory Limitations in Rule Learning

Adults, infants, and other species are able to learn and generalize abstract patterns from sequentially presented stimuli. Rule learning of this type may be involved in children's acquisition of linguistic structure, but the nature of the mechanisms underlying these abilities is unknown. While inferences regarding the capabilities of these mechanisms are commonly made based on the pattern of successes and failures in simple artificial-language rule-learning tasks, failures may be driven by memory limitations rather than intrinsic limitations on the kinds of computations that learners can perform. Here we show that alleviating memory constraints on adult learners through concurrent visual presentation of stimuli allowed them to succeed in learning regularities in three difficult artificial rule-learning experiments where participants had previously failed to learn via sequential auditory presentation. These results suggest that memory constraints, rather than intrinsic limitations on learning, may be a parsimonious explanation for many previously reported failures. We argue that future work should attempt to characterize the role of memory constraints in natural and artificial language learning.National Science Foundation (U.S.) (NSF DDRIG #0746251)United States. Department of Education (Jacob K. Javits Graduate Fellowship

Trypanosomes are monophyletic: evidence from genes for glyceraldehyde phosphate dehydrogenase and small subunit ribosomal RNA.

The genomes of Trypanosoma brucei, Trypanosoma cruzi and Leishmania major have been sequenced, but the phylogenetic relationships of these three protozoa remain uncertain. We have constructed trypanosomatid phylogenies based on genes for glycosomal glyceraldehyde phosphate dehydrogenase (gGAPDH) and small subunit ribosomal RNA (SSU rRNA). Trees based on gGAPDH nucleotide and amino acid sequences (51 taxa) robustly support monophyly of genus Trypanosoma, which is revealed to be a relatively late-evolving lineage of the family Trypanosomatidae. Other trypanosomatids, including genus Leishmania, branch paraphyletically at the base of the trypanosome clade. On the other hand, analysis of the SSU rRNA gene data produced equivocal results, as trees either robustly support or reject monophyly depending on the range of taxa included in the alignment. We conclude that the SSU rRNA gene is not a reliable marker for inferring deep level trypanosome phylogeny. The gGAPDH results support the hypothesis that trypanosomes evolved from an ancestral insect parasite, which adapted to a vertebrate/insect transmission cycle. This implies that the switch from terrestrial insect to aquatic leech vectors for fish and some amphibian trypanosomes was secondary. We conclude that the three sequenced pathogens, T. brucei, T. cruzi and L. major, are only distantly related and have distinct evolutionary histories

Identification of minimum phase preserving operators on the half line

Minimum phase functions are fundamental in a range of applications, including control theory, communication theory and signal processing. A basic mathematical challenge that arises in the context of geophysical imaging is to understand the structure of linear operators preserving the class of minimum phase functions. The heart of the matter is an inverse problem: to reconstruct an unknown minimum phase preserving operator from its value on a limited set of test functions. This entails, as a preliminary step, ascertaining sets of test functions that determine the operator, as well as the derivation of a corresponding reconstruction scheme. In the present paper we exploit a recent breakthrough in the theory of stable polynomials to solve the stated inverse problem completely. We prove that a minimum phase preserving operator on the half line can be reconstructed from data consisting of its value on precisely two test functions. And we derive an explicit integral representation of the unknown operator in terms of this data. A remarkable corollary of the solution is that if a linear minimum phase preserving operator has rank at least two, then it is necessarily injective.Comment: 17 page

Portable dynamic fundus instrument

A portable diagnostic image analysis instrument is disclosed for retinal funduscopy in which an eye fundus image is optically processed by a lens system to a charge coupled device (CCD) which produces recordable and viewable output data and is simultaneously viewable on an electronic view finder. The fundus image is processed to develop a representation of the vessel or vessels from the output data

Allelic segregation and independent assortment in <i>T. brucei</i> crosses: proof that the genetic system is Mendelian and involves meiosis

The genetic system on Trypanosoma brucei has been analysed by generating large numbers of independent progeny clones from two crosses, one between two cloned isolates of Trypanosoma brucei brucei and one between cloned isolates of T. b. brucei and Trypanosoma brucei gambiense, Type 2. Micro and minisatellite markers (located on each of the 11 megabase housekeeping chromosomes) were identified, that are heterozygous in one or more of the parental strains and the segregation of alleles at each locus was then determined in each of the progeny clones. The results unequivocally show that alleles segregate in the predicted ratios and that alleles at loci on different chromosomes segregate independently. These data provide statistically robust proof that the genetic system is Mendelian and that meiosis occurs. Segregation distortion is observed with the minisatellite locus located on chromosome I of T. b. gambiense Type 2 and neighboring markers, but analysis of markers further along this chromosome did not show distortion leading to the conclusion that this is due to selection acting on one part of this chromosome. The results obtained are discussed in relation to previously proposed models of mating and support the occurrence of meiosis to form haploid gametes that then fuse to form the diploid progeny in a single round of mating

Porous silica spheres as indoor air pollutant scavengers

Porous silica spheres were investigated for their effectiveness in removing typical indoor air pollutants, such as aromatic and carbonyl-containing volatile organic compounds (VOCs), and compared to the commercially available polymer styrene-divinylbenzene (XAD-4). The silica spheres and the XAD-4 resin were coated on denuder sampling devices and their adsorption efficiencies for volatile organic compounds evaluated using an indoor air simulation chamber. Real indoor sampling was also undertaken to evaluate the affinity of the silica adsorbents for a variety of indoor VOCs. The silica sphere adsorbents were found to have a high affinity for polar carbonyls and found to be more efficient than the XAD-4 resin at adsorbing carbonyls in an indoor environment

Life History of the Marine Isopod Cyathura polita in the Saint John River Estuary, New Brunswick: a Species at the Northern Extent of its Range

The marine isopod, Cyathura polita, inhabits estuaries on the east coast of North America from the Gulf of Mexico to the Bay of Fundy, Canada. We studied C. polita in the Saint John estuary to test for potential differences in life history that might occur because of the northern location of the population. In the Saint John, based on our interpretation from a six-month sampling program (May-October), the population exhibits a three-year life cycle, one year longer than more southern populations, and stretching over four summers. Our study supported the occurrence of protogynic hermaphroditism. After two summers as juveniles, individuals matured as females during their third summer, then displayed sex reversal by becoming males that fall, and finally reproducing as males in their fourth summer of life before death. Mean length of C. polita from the Saint John was greater than individuals from more southern populations (females, 13.8 &plusmn; 2.14 mm; males, 16.3 &plusmn; 2.41 mm). Annual brood release occurred in late July-early August. Mean fecundity of females was 53.2 &plusmn; 18.9 embryos per brood, which was greater than found in southern populations. Cyathura polita is rare in Canada and is known only from the Saint John and along the northern shore of the Bay of Fundy to the border of the United States