Showing papers by "University of Victoria published in 1992"

The lessons of learning: Reconciling theories of policy learning and policy change

Abstract: Several different explanations of policy change based on notions of learning have emerged in the policy literature to challenge conventional conflict-oriented theories. These include notions of ‘political-learning’ developed by Heclo, ‘policy-oriented learning’ developed by Sabatier, ‘lesson-drawing’ analyzed by Rose, ‘social learning’ discussed by Hall and ‘government learning’ identified by Etheredge. These different concepts identify different actors and different effects with each different type of learning. Some elements of these theories are compatible, while others are not. This article examines each approach in terms of who learns, what they learn, and the effects of learning on subsequent policies. The conclusion is that three distinct types of learning have often been incorrectly juxtaposed. Certain conceptual, theoretical and methodological difficulties attend any attempt to attribute policy change to policy learning, but this does not detract from the important reorientation of policy analysis that this approach represents.

Two Strikes Against Perfect Phylogeny

Abstract: One of the major efforts in molecular biology is the computation of phytogenies for species sets. A longstanding open problem in this area is called the Perfect Phylogeny problem. For almost two decades the complexity of this problem remained open, with progress limited to polynomial time algorithms for a few special cases, and many relaxations of the problem shown to be NP-Complete. From an applications point of view, the problem is of interest both in its general form, where the number of characters may vary, and in its fixed-parameter form. The Perfect Phylogeny problem has been shown to be equivalent to the problem of triangulating colored graphs[30]. It has also been shown recently that for a given fixed number of characters the yes-instances have bounded treewidth[45], opening the possibility of applying methodologies for bounded treewidth to the fixed-parameter form of the problem. We show that the Perfect Phylogeny problem is difficult in two different ways. We show that the general problem is NP-Complete, and we show that the various finite-state approaches for bounded treewidth cannot be applied to the fixed-parameter forms of the problem.

Short-term longitudinal change in cognitive performance in later life.

Abstract: Changes in mean performance on memory, information processing, and intellectual ability tasks over a 3-year period were examined. The sample consisted of 328 community-dwelling men and women (from an original sample of 484 individuals) aged 55-86 years. Ss completed tasks yielding measures of verbal processing time, working memory, implicit memory, vocabulary, verbal fluency, world knowledge, reading comprehension, word recall, and text recall. The results showed significant average decline on working memory, verbal fluency, and world knowledge. There were also interactions for 2 processing time measures and working memory, showing greater decline in the earlier-born cohort group than in the later-born cohort group. A step-down analysis revealed that covarying declines in other variables, including processing time, did not eliminate significant declines in working memory, verbal fluency, and world knowledge.

Permittivity measurements using open-ended sensors and reference liquid calibration-an uncertainty analysis

Abstract: Results of the uncertainty analysis of the error-corrected permittivity measurements of materials using open-ended sensors are reported. Uncertainties in the permittivities of the reference liquids due to the uncertainties in the Cole-Cole parameters are discussed. The effect of the selection of these parameters of reference liquids, when used as calibration standards for error-corrected permittivity measurements, is highlighted. The results of measurements performed on 15 and 30 ppt saline test liquids are presented along with the measurement uncertainties resulting from uncertainties in the Cole-Cole parameters of the reference liquids. >

Biochemical and environmental perspectives on nitrogen metabolism in fishes

Abstract: Catabolism of nitrogen-containing substances makes a major contribution to the oxidative metabolism in teleostean fishes. In this review, we focus on aspects of the formation, transport, detoxification and excretion of the two most important nitrogenous products of fishes: ammonia (NH3 plus NH4+) and urea. While NH4+ makes up the bulk of nitrogenous waste, it is in equilibrium with the highly toxic NH3. Ammonia is generated in the liver and excreted through branchial, surface and renal routes. Innocuous urea is derived through hepatic uricolysis or argininolysis and voided through kidney, gill, skin or faeces. Under conditions hampering the release of ammonia, such as exposure to exogenous ammonia, water limitation, or alkaline conditions, some teleosts detoxify ammonia through synthesis of urea by the ornithine-urea cycle in liver. Ammonia and possibly alanine are the prevalent vehicles of internal nitrogen transport. Glutamine is immaterial to interorgan nitrogen transport in fishes, but plays a transient role in the detoxification of ammonia by brain glutamine synthetase.

Photodecarboxylation: mechanism and synthetic utility

Abstract: The mechanistic aspects of photodecarboxylation are examined with respect to the mode of bond cleavage. Emphasis is placed on recent studies of aromatic substrates. The synthetic utility of photodecarboxylation is discussed with emphasis on reactions of carbon radicals generated via photodecarboxylation.

Distinct sequence of gonadotropin-releasing hormone (GnRH) in dogfish brain provides insight into GnRH evolution.

Abstract: In vertebrates, gonadotropin-releasing hormone (GnRH) belongs to a family of decapeptides characterized by the conservation of residues 1, 2, 4, 9, and 10. In the jawed vertebrates only positions 5, 7, and 8 in the GnRH molecules vary. We have now purified two forms of GnRH from the brains of spiny dogfish (Squalus acanthias) by using reverse-phase high-performance liquid chromatography. The primary structures were established by automated Edman degradation and mass spectral analysis. The distinct structure of the first form (dogfish GnRH) is pGlu-His-Trp-Ser-His-Gly-Trp-Leu-Pro-Gly-NH2 (pGlu represents pyroglutamyl). The second peptide is identical to a form of GnRH originally isolated from chicken brains (chicken GnRH-II; pGlu-His-Trp-Ser-His-Gly-Trp-Tyr- Pro-Gly-NH2) and is widespread throughout the vertebrates. We are aware of no other species of cartilaginous fish in which the primary structures of two forms of GnRH have been determined. The presence of chicken GnRH-II in dogfish supports the idea that chicken GnRH-II is the oldest GnRH to evolve in jawed vertebrates. With the addition of the dogfish GnRH structure to the family, two main structural branches of GnRH can be delineated. The physiological effects of dogfish GnRH included the release of not only gonadotropin but also growth hormone from goldfish pituitary fragments.

Injuries on stickleback from attacks by a toothed predator (oncorhynchus) and implications for the evolution of lateral plates.

Abstract: in Relation to Sex, Second Edition. John Murray, London, UK. ENDLER, J. A. 1986. Natural Selection in the Wild. Princeton University Press, Princeton, NJ USA. LANDE, R., AND S. J. ARNOLD. 1983. The measurement of selection on correlated characters. Evolution 37:1210-1226. MADSEN, T. 1987. Natural and sexual selection in grass snakes, Natrix natrix, and adders, Vipera berus. Ph.D. Diss., University of Lund, Lund, Sweden. 1988. Reproductive success, mortality and sexual size dimorphism in the adder, Vipera berus. Holarctic Ecology 11:77-80. MADSEN, T., AND B. STILLE. 1988. The effect of size dependent mortality on colour morphs in male adders, Vipera berus. Oikos 52:73-78. MADSEN, T., R. SHnE, J. LoMArN, AND T. HAKANSSON. 1992. Determinants of mating success in male adders (Vipera berus). Anim. Behav. In press. PRESTT, I. 1971. An ecological study of the viper, Vipera berus, in southern Britain. J. Zool. 164:373418. STILLE, B., T. MADSEN, AND M. NIKLASSON. 1986. Multiple paternity in the adder, Vipera berus. Oikos 47:173-175. TURELLI, M., J. H. GILLESPIE, AND R. LANDE. 1988. Rate tests for selection on quantitative characters during macroevolution and microevolution. Evolution 42:1085-1089.

Geophysical support for aqueous fluids in the deep crust: seismic and electrical relationships

Abstract: SUMMARY studies have shown that up to a few per cent porosity filled with saline fluid in the lower crust can explain many of the regions with: (1) low electrical resistivities, (2) velocities that appear to be too low for the otherwise inferred mafic composition, and (3) strong lower crustal reflectivity. Several predictions of the free porosity model are examined in this article. A compilation of approximately coincident magnetotelluric electrical resistivity and refraction seismic velocity data for the lower continental crustjs presented to test the predicted correlation. In spite of the limited geographically coincident data and the difficulties of ensuring accurate depth coincidence and of anisotropy effects, there is a general trend of decreasing velocity with decreasing resistivity. The data are scattered, but most fall between the reasonable bounds provided by pore geometry models with effective aspect ratio (for velocity) and Archie's Law pore tortuosity exponent (for resistivity) pairs of 0.03 : 2.0 and 0.1 : 1.5 respectively. As in previous compilations, shield areas tend to have both higher resistivities and higher velocities in the lower crust compared to Phanerozoic areas, although there is overlap for both parameters. A general correlation is also found between the top of low resistivity layers and the top of lower crustal reflective zones with the 400-450 "C isotherms. Possible explanations of this correlation with temperature include (1) an association with the brittleductile transition, below which pore geometries are such as to hold fluid in the required configuration, and (2) control provided by metamorphic reactions that restrict free fluid to below this depth. To constrain better the pore geometry, a compilation of the limited data on lower crustal Poisson's ratio shows most values -0.28. This is consistent with a mainly mafic composition with up to several per cent porosity. Reasonable pore geometry distributions predict a small decrease or constant Poisson's ratio with increasing porosity. While each of the three lower crustal geophysical data types have other reasonable explanations, the apparent correlations above provide support for the fluid-filled pores in the lower crust. The problems of the low permeability required to keep fluid in the lower crust, and of pore fluid consumption in retrograde metamorphic reactions during cooling are discussed briefly. Two mechanisms are suggested as means of producing a low-permeability cap in the middle to deep crust: one invokes deformation of textural equilibrium pore geometries by small deviatoric stresses, the other lower crustal shear processes. There remains some difficulty in reconciling free aqueous fluids in the lower crust with the expected retrograde metamorphism that should take up water into hydrated mineral assemblages.

A strong biological response to oceanic flow past Cobb Seamount

Abstract: We report results of a CTD and chlorphyll a survey from Cobb Seamount, a shallow seamount in the northeast Pacific. Our results show a several-fold increasein the standing crop of chlorophyll a is centred over the seamount. Current meter and drifter data indicate an anticyclonic deflection of deep currents around consistent with a theoretical stratified Tylor cone. Cobb differs from other seamounts where similar phenomena have been reported (O wens and H ogg ; 1980, Deep-Sea Research, 27, 1029–1045; Gould et al., 1981, Deep-Sea Research, 28, 409–440; Genin and Boehlert , 1985, Journal of Marine Research, 43, 907–924) in that its summit penetrates well into the euphotic zone. A Taylor column existing at such shallow depths could locally enhance primary production, providing a significant source of energy for higher trophic levels on the seamount. Indirect evidence for such a scenario comes from observations of a high biomass benthic community on Cobb Seamount.

Detection of Aeromonas salmonicida from fish by using polymerase chain reaction amplification of the virulence surface array protein gene.

Abstract: A DNA-based assay was developed to detect Aeromonas salmonicida from infected fish by analyzing tissues, feces, and the tank water in which the infected fish were held. This analysis was done both by direct detection from samples and after a bacterial outgrowth step. Polymerase chain reaction (PCR) amplification of a 421-bp sequence from the 3' region of the surface array protein gene (vapA) of A. salmonicida provided a specific and sensitive method for the detection and identification of this important fish pathogen. The sensitivity of PCR detection of A. salmonicida directly from tissues was less than 10 CFU/mg. Furthermore, a detection level of 5 fg, equivalent to approximately 1 cell, was obtained by using purified chromosomal DNA as the template. This highly reproducible assay, which requires 45 min to complete, is therefore sensitive enough to be used as a noninvasive method for monitoring fish populations for the presence of carrier fish. Because the surface protein array (A-layer) is a virulence factor of A. salmonicida, PCR analysis with oligonucleotide primers directed at vapA can also be used to provide information on the potential virulence of a strain.

Surviving on the Street: The Experiences of Homeless Youth

Abstract: This article documents the living conditions of a sample of adolescents (N = 390) who had left home and were living on the street in Toronto, Canada The majority of these youth had spenta considerable amount of time without adequate shelter, food, or income; furthermore, many were involved in a variety of illegal activities and had been incarcerated or suicidal Multiple regression analyses revealed that the most consistent predictors of hunger, criminal activity, and incarceration were conditions of street life itself: thelack of secure shelter and the length of time on the street. Overal4 the living conditions of these youth closely parallel those of homeless adults. Although there are differences between adults and adolescents who live on the street, the similarities suggest that it may be inappropriate to label the latter runaways and to consistently separate adults and adolescents into two completely distinct homeless populations.

Growth inhibition of Francisella tularensis live vaccine strain by IFN-gamma-activated macrophages is mediated by reactive nitrogen intermediates derived from L-arginine metabolism.

Abstract: We have examined the abilities of the recombinant murine lymphokines IFN-gamma, granulocyte-macrophage (GM)-CSF, and IL-4 to stimulate the in vitro antimicrobial activity of macrophages against the live vaccine strain (LVS) of Francisella tularensis Resident peritoneal macrophages from C57BL/6 strain mice were cultured overnight with IFN-gamma, GM-CSF, or IL-4, and then infected with LVS In macrophages treated with IFN-gamma, the growth of LVS was suppressed by a factor of 100- to 1000-fold in comparison with untreated cells This effect was dose-dependent and was enhanced by the addition of LPS In contrast, macrophages treated with either GM-CSF or IL-4 exhibited no such enhanced antitularemic activity, even in the presence of LPS Because reactive nitrogen intermediates derived from L-arginine metabolism have been implicated in the killing of various infectious organisms, we evaluated the possibility that such a mechanism might contribute to the antitularemic activity of IFN-gamma-stimulated macrophages Macrophages were treated with NG-monomethyl-L-arginine (NMMA), an inhibitor of L-arginine metabolism in mammalian cells, during the activation procedure and throughout the course of infection NMMA had no effect on the growth of LVS in unstimulated macrophages In macrophages activated with IFN-gamma, however, NMMA suppressed their capacity to inhibit LVS growth This effect was proportional to the dose of NMMA added and reversible by supplementing the medium with additional L-arginine, and there was a direct correlation between the production of nitrite by activated macrophages and their ability to inhibit LVS growth Furthermore, the growth of LVS was inhibited by nitrogen metabolites in a cellfree system The results of this study indicate that the mechanism of action of IFN-gamma on the resistance of macrophages to LVS growth is related, at least in part, to the production of reactive nitrogen metabolites

Mother-Offspring Separation and Acoustic Stereotypy: a Comparison of Call Morphology in Two Species of Pinnipeds

Abstract: I have compared structural variation of the primary vocalizations used between mother-offspring pairs in two species of pinnipeds that differ fundamentally in their breeding behaviour: northern elephant seal (Mirounga angustirostris) mothers and offspring normally are together throughout the nursing period; northern fur seal (Callorhinus ursinus) females regularly separate from their offspring while nursing. Two predictions were tested: (1) these vocalizations should be individually-distinct (stereotyped) in females and pups of both species if they serve to function for recognition, and (2) because individuality should be more pronounced in a species where separations and reunions are common, the vocalizations used between northern fur seal mother-offspring pairs should be more individually-stereotyped than those of the northern elephant seal. Principal components analyses revealed structural differences between the calls of females and pups in both species. Analysis of variance showed the calls of individual seals to be acoustically distinct in all cases. The calls used between mother-offspring pairs of northern fur seals were more stereotyped than those of northern elephant seals. These calls had less within-individual variation, greater among-individual variation and were more often correctly predicted in discriminant analyses. The results indicate that selective pressure to develop vocal recognition exists in both species but is greater in the northern fur seal.

Integrating Constraints with an Object-Oriented Language

Abstract: Constraints are declarative statements of relations among elements of the language's computational domain, e.g., integers, booleans, strings, and other objects. Orthogonally, the tools of object-oriented programming, including encapsulation, inheritance, and dynamic message binding, provide important mechanisms for extending a language's domain. Although the integration of constraints and objects seems obvious and natural, one basic obstacle stands in the way: objects provide a new, larger, computational domain, which the language's embedded constraint solver must accommodate. In this paper we list some goals and non-goals for an integration of constraints and object oriented language features, outline previous approaches to this integration, and describe the scheme we use in Kaleidoscope'91, our object-oriented constraint imperative programming language. Kaleidoscope'91 uses a class-based object model, multi-methods, and constraint constructors to integrate cleanly the encapsulation and abstraction of a state-of-the-art object-oriented language with the declarative aspects of constraints.

Spectroscopic study of the activation and oligomerization of the channel-forming toxin aerolysin: identification of the site of proteolytic activation.

Abstract: The channel-forming protein aerolysin is secreted as a protoxin which can be activated by proteolytic removal of a C-terminal peptide. The activation and subsequent oligomerization of aerolysin were studied using a variety of spectroscopic techniques. Mass spectrometric determination of the molecular weights of proaerolysin and aerolysin permitted identification of the sites at which the protoxin is processed by trypsin and chymotrypsin. The results of far- and near-UV circular dichroism measurements indicated that processing with trypsin does not lead to major changes in secondary or tertiary structure of the protein. An increase in tryptophan fluorescence intensity and a small red shift in the maximum emission wavelength of tryptophans could be observed, suggesting that there is a change in the environment of some of the tryptophans. There was also a dramatic increase in the binding of the hydrophobic fluorescent probe 1-anilino-8-naphthalenesulfonate during activation, leading us to conclude that a hydrophobic region in the protein is exposed by trypsin treatment. Using measurements of light scattering, various parameters influencing oligomerisation of trypsin-activated aerolysin were determined. Oligomerization rates were found to increase with the concentration of aerolysin, whereas they decreased with increasing ionic strength.

A Study of charged particle multiplicities in hadronic decays of the Z0

Abstract: We present an analysis of multiplicity distributions of charged particles produced inZ 0 hadronic decays. The results are based on the analysis of 82941 events collected within 100 MeV of theZ 0 peak energy with the OPAL detector at LEP. The charged particle multiplicity distribution, corrected for initial-state radiation and for detector acceptance and resolution, was found to have a mean 〈n ch〉=21.40±0.02(stat.)±0.43(syst.) and a dispersionD=6.49±0.02(stat.)±0.20(syst.). The shape is well described by the Lognormal and Gamma distributions. A negative binomial parameterisation was found to describe the shape of the multiplicity distribution less well. A comparison with results obtained at lower energies confirms the validity of KNO(-G) scaling up to LEP energies. A separate analysis of events with low sphericity, typically associated with two-jet final states, shows the presence of features expected for models based on a stochastic production mechanism for particles. In all cases, the features observed in the data are well described by the Lund parton shower model JETSET.

Thin aggregative fimbriae from diarrheagenic Escherichia coli.

Abstract: Four strains of diarrheagenic Escherichia coli originally isolated from distinct geographic regions were found to produce unusual thin aggregative fimbriae requiring depolymerization in formic acid prior to analysis by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Immunoelectron microscopy of native fimbriae and Western blot (immunoblot) analysis of the corresponding 18-kDa fimbrins showed that these E. coli fimbriae were serologically cross-reactive with SEF 17 (Salmonella enteritidis fimbriae with a fimbrin molecular mass of 17 kDa). The E. coli and S. enteritidis fimbrins had similar total amino acid compositions and highly conserved N-terminal amino acid sequences. These results indicate that E. coli and S. enteritidis produce biochemically related, aggregative fimbriae which constitute a new type of intergenerically distributed fimbriae for which we propose the descriptive name GVVPQ fimbriae on the basis of the conserved N-terminal amino acid sequence.

A reverse engineering environment based on spatial and visual software interconnection models

Abstract: Reverse engineering is the process of extracting system abstractions and design information out of existing software systems. This information can then be used for subsequent development, maintenance, re-engineering, or reuse purposes. This process involves the identification of software artifacts in a particular subject system, and the aggregation of these artifacts to form more abstract system representations. This paper describes a reverse engineering environment which uses the spatial and visual information inherent in graphical representations of software systems to form the basis of a software interconnection model. This information is displayed and manipulated by the reverse engineer using an interactive graph editor to build subsystem structures out of software building blocks. The spatial component constitutes information about how a software structure looks. The coexistence of these two representations is critical to the comprehensive appreciation of the generated data, and greatly benefits subsequent analysis, processing, and decision-making.

Secondary mesenchyme of the sea urchin embryo: ontogeny of blastocoelar cells.

Abstract: Secondary mesenchyme in sea urchin embryos is released into the blastocoel after primary mesenchyme, and although these cells have been recognized for some time, we lack knowledge about many fundamental aspects of their origin and fate. Here we documented the ontogeny of one of the principal, and least well-known, types of cells derived from secondary mesenchyme. The blastocoelar cells arise from mesenchyme released from the tip of the archenteron following the initial phase of gastrulation. The cells migrate with their cell bodies suspended in the blastocoel, rather than being apposed to the basal lamina like primary mesenchyme. The cells extend numerous fine filopodia to form a network of cytoplasmic processes around the gut, along the skeletal rods, and within the larval arms. Once the network is formed, the cells maintain their positions, although they actively translocate vesicles and cytoplasm along their filopodia. Cell counts indicate there is an initial recruitment of cells during gastrulation, followed by a more gradual increase in cell number after the larva begins to feed. Lineage studies in which 16-cell-stage macromeres were injected with horseradish peroxidase indicate that almost all of the macromere-derived mesenchyme forms pigment cells and blastocoelar cells. We propose that blastocoelar cells are a distinct subset of secondary mesenchyme that forms fibroblast-like cells in the blastocoel of sea urchin embryos. © 1992 Wiley-Liss, Inc.

Wave propagation in fluid filled nonlinear viscoelastic tubes

Abstract: The present work considers one dimensional wave propagation in an infinitely long, straight and homogeneous nonlinear viscoelastic tube filled with an incompressible, inviscid fluid. In order to include the geometric dispersion in the analysis, the tube wall inertia effects are added to the pressure-area relation. Using the reductive perturbation technique, the propagation of weakly nonlinear waves in the long-wave approximation is examined. In the long-wave approximation, a general equation is obtained, and it is shown that by a proper scaling this equation reduces to the well-known nonlinear evolution equations. Intensifying the effect of nonlinearity in the perturbation process, the modified forms of these evolution equations are also obtained. In the absence of nonlinear viscoelastic effects all the equations reduce to those of the linear viscoelastic tube.

Bilateral knife cuts to the perforant path disrupt spatial learning in the Morris water maze.

Abstract: Both the hippocampus and the entorhinal cortex are known to be crucial for spatial learning, but the contribution of the pathway linking the two structures, the perforant path (PP), has never been tested in a spatial learning paradigm. The present study examined the role of the PP in spatial learning using the Morris water maze. Seven days after bilateral transection of the PP with a fine-bladed knife, rats were habituated to the pool, then trained to swim from varying start locations to a platform submerged in a fixed location. After 28 training trials over 5 days, probe trials (without any platform present) were given to assess spatial memory for the location. Compared to sham-operated controls, lesioned rats showed slower learning and poorer asymptotic performance in terms of both swim path distance and escape latency, and less preference for the correct quadrant during probe trials. When the platform location was "reversed" to the opposite quadrant, the lesioned rats again showed poorer learning, poorer asymptotic performance, and reduced preference for the correct quadrant on the probe trial. When tested with a visible platform whose position varied from trial to trial, lesioned rats performed as well as controls. These results are congruent with previous analyses of the contributions of the entorhinal cortex and hippocampus to spatial learning and suggest that for spatial learning, the PP is a critical functional link between these two structures.

Production of a conserved adhesin by the human gastroduodenal pathogen Helicobacter pylori.

Abstract: An adhesin protein with an approximate subunit molecular weight of 19,600 has been purified from the gastric pathogen Helicobacter pylori. The protein was loosely associated with the cell surface and was removed by gentle stirring or shearing. Released aggregates of the 19.6-kDa protein were removed from suspension by ultracentrifugation and separated from contaminating membranes by washing in 1.0% sodium dodecyl sulfate (SDS). The SDS-insoluble protein was purified further by Mono Q anion-exchange column chromatography. Electron microscopy of the purified adhesin demonstrated that it formed amorphous aggregates similar to the material attached to the bacterial cells and that the aggregates were morphologically distinct from typical fimbriae. Western blot (immunoblot) analysis with antiserum raised against the purified protein from one strain reacted with a protein with a similar subunit molecular weight present in all nine strains of H. pylori examined, but the protein was not present in other Helicobacter species examined. The N-terminal sequences of the 19.6-kDa protein purified from three different strains of H. pylori were identical for the first 28 amino acids, with the 10 amino-terminal residues showing limited sequence homology with the TcpA pilus protein of Vibrio cholerae. The H. pylori 19.6-kDa protein associated both with human and rabbit erythrocytes and with human buccal epithelial cells. Polystyrene microspheres coated with the protein agglutinated human, horse, and rabbit erythrocytes, suggesting that this protein species could mediate adhesion between H. pylori and eucaryotic cells. This ability to act as an adhesin may make this protein an important virulence factor for H. pylori and hence a potential target for a vaccine and therapy.

Rareness as an Antipredator Strategy to Reduce Predation Risk for Moose and Caribou

Abstract: The densities of moose (Alces alces) and woodland caribou (Rangifer tarandus) are low in Canada and Alaska (caribou- -0.03-0.13/km2, moose- -0.1-0.5/km2) in systems where wolves (Canis lupus) are unexploited; hence these ungulates are far below a food carrying capacity (K) of ≥1.5/km2. Cow moose and caribou migrate prior to parturition seeking birth sites to reduce predation risk and show philopatry. This spacing-out results in damping the predation of neonates and can provide a stabilizing recruitment (R s ), where R s equals the annual natural mortality (M) of adults (R = M,λ = 1.00). These stabilizing recruitments at 6–9 months-of-age for moose were ~ 25–26 calves/100 females, and for caribou were 15–16% calves of the population (25–26 calves/100 females). The R s values resulted only when the densities of ungulates were low in systems where wolves were common and fluctuations in R (greater and less than R s ) occurred around a mean density defined as the stabilizing density (D s ). A phase plane analysis of the isocline of the abundance of wolves on prey was oblique, and when moose were the prey, was tangent to the moose isocline in the range of 0.2–.5/km2. Such predator-prey interactions should result in low stable equilibria for moose populations with reduced chances for extinctions. However, for caribou coexisting with moose populations, extinction is a distinct possibility, especially in isolated populations where recolonization is precluded.

Design of linear-phase IIR filters via impulse-response gramians

Abstract: A new method for the design of a linear-phase infinite-impulse-response (IIR) filter is presented. It involves designing a finite-impulse-response (FIR) filter satisfying the given frequency response specifications and subsequently obtaining a significantly lower order IIR filter using model reduction based on impulse-response gramians. The general outline of the method and a brief overview of the existing linear-phase FIR filter design and model-reduction techniques are presented. The impulse-response gramian and the model-reduction algorithm used are presented. The method is illustrated by design examples and is compared with other methods for the design of linear-phase IIR filters using equalizers. >