bluuebunny/crossref_metadata_2025_split huggingface dataset:
On the relationship between µ-invariant measures and quasi-stationary distributions for continuous-time Markov chains
Authors: Nair M. G. , Pollett P. K. 
Published: April 2006

In a recent paper, van Doorn (1991) explained how quasi-stationary distributions for an absorbing birth-death process could be determined from the transition rates of the process, thus generalizing earlier work of Cavender (1978). In this paper we shall show that many of van Doorn's results can be extended to deal with an arbitrary continuous-time Markov chain over a countable state space, consisting of an irreducible class, C, and an absorbing state, 0, which is accessible from C. Some of our results are extensions of theorems proved for honest chains in Pollett and Vere-Jones (1992).In Section 3 we prove that a probability distribution on C is a quasi-stationary distribution if and only if it is a µ-invariant measure for the transition function, P. We shall also show that if m is a quasi-stationary distribution for P, then a necessary and sufficient condition for m to be µ-invariant for Q is that P satisfies the Kolmogorov forward equations over C. When the remaining forward equations hold, the quasi-stationary distribution must satisfy a set of ‘residual equations' involving the transition rates into the absorbing state. The residual equations allow us to determine the value of µ for which the quasi-stationary distribution is µ-invariant for P. We also prove some more general results giving bounds on the values of µ for which a convergent measure can be a µ-subinvariant and then µ-invariant measure for P. The remainder of the paper is devoted to the question of when a convergent µ-subinvariant measure, m, for Q is a quasi-stationary distribution. Section 4 establishes a necessary and sufficient condition for m to be a quasi-stationary distribution for the minimal chain. In Section 5 we consider ‘single-exit' chains. We derive a necessary and sufficient condition for there to exist a process for which m is a quasi-stationary distribution. Under this condition all such processes can be specified explicitly through their resolvents. The results proved here allow us to conclude that the bounds for µ obtained in Section 3 are, in fact, tight. Finally, in Section 6, we illustrate our results by way of two examples: regular birth-death processes and a pure-birth process with absorption.
Stochastic monotonicity and conditional Monte Carlo for likelihood ratios
Authors: Glasserman Paul 
Published: April 2006

Likelihood ratios are used in computer simulation to estimate expectations with respect to one law from simulation of another. This importance sampling technique can be implemented with either the likelihood ratio at the end of the simulated time horizon or with a sequence of likelihood ratios at intermediate times. Since a likelihood ratio process is a martingale, the intermediate values are conditional expectations of the final value and their use introduces no bias.We provide conditions under which using conditional expectations in this way brings guaranteed variance reduction. We use stochastic orderings to get positive dependence between a process and its likelihood ratio, from which variance reduction follows. Our analysis supports the following rough statement: for increasing functionals of associated processes with monotone likelihood ratio, conditioning helps. Examples are drawn from recursively defined processes, Markov chains in discrete and continuous time, and processes with Poisson input.
The herbarium and botanical art of Hendrik Elingsz van Rijgersma
Authors: Ehn Mia , Zanoni Thomas A. 
Published: April 2006

AbstractA herbarium collected by H. E. van Rijgersma in the Caribbean island St. Martin 1865–1868 and 1875 has been found at the Swedish Museum of Natural History (S), Stockholm. The other known collection of van Rijgersma's plants was housed in Berlin (B), but was destroyed in World War II. Specimens collected by him are also kept in Leiden (L). Many of the Stockholm sheets have original illustrations by van Rijgersma in either black and white or in full watercolour, or both. A checklist of specimens and illustrations is presented at http://www.nrm.se/fbo/hist/rijgersma/rijgersma.html.en
Ecogeographic surveys as tools for analyzing potential reproductive isolating mechanisms: an example using Solanum juglandifolium Dunal, S. ochranthum Dunal, S. lycopersicoides Dunal, and S. sitiens I. M. Johnston
Authors: Smith Stacey D. , Peralta Iris Edith 
Published: April 2006

AbstractAn ecogeographic survey was completed for two pairs of South American Solanum species: (1) S. juglandifolium and S. ochranthum, and (2) S. lycopersicoides and S. sitiens. The purpose of this survey was to characterize the distribution, ecology, and phenology of these species and to screen for factors that might constitute premating reproductive isolating mechanisms between each pair. Passport data from 276 herbarium specimens were entered into a database, which was subsequently analyzed to determine the ecogeographic distribution and phenology of the surveyed species. The differences between species uncovered by the survey were then considered in the context of reproductive isolation. As S. juglandifolium and S. ochranthum were found to have overlapping ecogeographic preferences and phenology, it was postulated that postmating isolating mechanisms form the principal barrier to hybridization between the two species. Unlike S. juglandifolium and S. ochranthum, S. lycopersicoides and S. sitiens differed markedly in ecogeographic distribution. The species have been successfully crossed several times artificially, so the differences in distribution found in this survey probably contribute to maintaining species barriers between the two. In summary, this ecogeographic survey provided a useful method for analyzing the potential for interspecific gene flow between closely related taxa.
Xerophyta seinei (Velloziaceae), a distinctive new species from Zimbabwe
Authors: Behnke H.-Dietmar , Kramer Klaus , Hummel Eric 
Published: April 2006

AbstractXerophyta seinei Behnke, K. Kramer & E. Hummel sp. nov. (Velloziaceae), a new species from the Rhodes Matopos National Park in southwestern Zimbabwe, is distinguished by persistent leaf blades concealing the stems, an apex of dark­green leaves with lustrous and glutinous upper surfaces, and a lamina with glands on both surfaces and with non­transcurrent vascular bundles. Its distinctness from other Xerophyta species is also substantiated by specific sieve­element plastids (with a rectangular protein crystal in addition to the angular ones common to Velloziaceae) and by an rbcL­analysis. The morphology and leaf anatomy of the new species are compared to those of other members of the family and, in particular, of Xerophyta species known from the area.
Two new species of Campanulaceae from South Africa
Authors: Hong De-Yuan 
Published: April 2006

AbstractTwo new species in Campanulaceae, Theilera capensis D.Y. Hong and Craterocapsa alfredica D.Y. Hong, are described from South Africa. Theilera capensis is different from T. guthriei in having oblong leaves on short branches, corolla lobes nearly as long as the tube, filaments conspicuously dilated, and an annular disc. Craterocapsa alfredica is relatively close to C. insizwae, but differs from it in having ovate or ovate‐lanceolate leaves, narrow‐lanceolate calyx lobes, and a 3‐lobed stigma.
Typification of names of lichen taxa described by G. Sampaio and some others, deposited in Porto Herbarium (PO)
Authors: Paz-Bermúdez Graciela , Aguiar-Branco Helena , Folhadela Elisa 
Published: April 2006

AbstractGonçalo Sampaio authored 103 new names of lichens, comprising one new genus, 60 new species, 14 new infraspecific taxa, 25 new combinations and two nomina nova. In addition, he proposed 42 "names" that were not validly published, 18 of these being simple nomina nuda and 21 apparently representing invalid attempts to publish new combinations. The type material is deposited in the Herbarium of University of Porto (PO), except in three cases. Apart from a few specimens from Spain, the material derives from Portugal. For the names of all new taxa the type collections are listed, either a holotype or a lectotype (usually here designated). In addition, a few lichen names authored by Maurice Bouly de Lesdain or William Nylander and based on Portuguese material preserved at PO are listed with indications of type.
Approximations to densities in geometric probability
Authors: Solomon H. , Stephens M. A. 
Published: April 2006

Many random variables arising in problems of geometric probability have intractable densities, and it is very difficult to find probabilities or percentage points based on these densities. A simple approximation, a generalization of the chi-square distribution, is suggested, to approximate such densities; the approximation uses the first three moments. These may be theoretically derived, or may be obtained from Monte Carlo sampling.The approximation is illustrated on random variables (the area, the perimeter, and the number of sides) associated with random polygons arising from two processes in the plane. Where it can be checked theoretically, the approximation gives good results. It is compared also with Pearson curve fits to the densities.
A semi-Markov model for a multigrade population with Poisson recruitment
Authors: McClean Sally I. 
Published: April 2006

We consider a multigrade population with semi-Markov transitions between grades, Poisson arrivals to each grade, and departures from each grade. For this model the joint distribution of the numbers in each grade at any time is found, and the limiting distributions shown to be independently Poisson; this extends a previous result for a multigrade population with Markov transitions and Poisson recruitment.This model is particularly applicable to manpower planning. The inclusion of semi-Markov transitions allows us to take into account existing knowledge of the distribution of length of service until an individual leaves his firm.
On the normal convergence of a class of simple batch epidemics
Authors: Langberg Naftali A. 
Published: April 2006

A group of n susceptible individuals exposed to a contagious disease is considered. It is assumed that at each instant in time one or more susceptible individuals can contract the disease.The progress of this epidemic is modeled by a stochastic process Xn(t), t in [0,∞) representing the number of infective individuals at time t. It is shown that Xn(t), with the suitable standardization and under a mild condition, converges in distribution as n → ∞to a normal random variable for all t in (0, t0), where t0 is an identifiable number.
A piecewise Markovian model for simulated annealing with stochastic cooling schedules
Authors: Kolonko M. 
Published: April 2006

We introduce a stochastic process with discrete time and countable state space that is governed by a sequence of Markov matrices . Each Pm is used for a random number of steps Tm and is then replaced by Pm+1. Tm is a randomized stopping time that may depend on the most recent part of the state history. Thus the global character of the process is non-Markovian.This process can be used to model the well-known simulated annealing optimization algorithm with randomized, partly state depending cooling schedules. Generalizing the concept of strong stationary times (Aldous and Diaconis [1]) we are able to show the existence of optimal schedules and to prove some desirable properties. This result is mainly of theoretical interest as the proofs do not yield an explicit algorithm to construct the optimal schedules.
Putting more eggs in the best basket: clutch‐size regulation in the comma butterfly
Authors: Bergström Anders , Janz Niklas , Nylin Sören 
Published: April 2006

Abstract.  1. Many studies have identified different factors influencing clutch‐size regulation, primarily within various groups of insects. One prediction is that ovipositing females should increase clutch size with host quality. However, in many studies it is not clear whether ovipositing females are responding to host quality or quantity.2. Females of the polyphagous comma butterfly, Polygonia c‐album (L.), were allowed to oviposit on two hosts differing greatly in quality: the preferred host, stinging nettle (Urtica dioica L.), and the low‐ranked host, birch (Betula pubescens Ehrh). Ovipositing females were observed visually and clutch sizes were recorded. The experiment was repeated in three different years; in total, 938 observations of oviposition events were made.3. In all three years, females ovipositing on U. dioica laid larger clutches (median 1.6–1.85) compared with females ovipositing on B. pubescens (median 1.0–1.3). The difference was significant in two out of three years and when all three years were pooled.4. Thus, P. c‐album females exhibit clutch‐size regulation, with larger clutches on better hosts. It is suggested that the proximate mechanism is likely to be a response to the same stimuli used for female ranking of host plants in the preference hierarchy.
Genetic signature of recent glaciation on populations of a near‐shore marine fish species (Syngnathus leptorhynchus)
Authors: WILSON A. B. 
Published: April 2006

AbstractContinental glaciation has played a major role in shaping the present‐day phylogeography of freshwater and terrestrial species in the Northern Hemisphere. Recent work suggests that coastal glaciation during ice ages may have also had a significant impact on marine species. The bay pipefish,Syngnathus leptorhynchus, is a near‐shore Pacific coast fish species with an exceptionally wide latitudinal distribution, ranging from Bahia Santa Maria, Baja California to Prince William Sound, Alaska. Survey data indicate thatS. leptorhynchusis experiencing a range expansion at the northern limit of its range, consistent with colonization from southern populations. The present study uses six novel microsatellite markers and mitochondrial DNA (mtDNA) sequence data to study the present‐day population genetic structure of four coastal populations ofS. leptorhynchus. Deficits in mtDNA and nuclear DNA diversity in northern populations from regions glaciated during the last glacial maximum (LGM) [c. 18 000 years before present (bp)] suggest that these populations were effected by glacial events. Direct estimates of population divergence times derived from both isolation and isolation‐with‐migration models of evolution are also consistent with a postglacial phylogenetic history of populations north of the LGM. Sequence data further indicate that a population at the southern end of the species range has been separated from the three northern populations since long before the last interglacial event (c. 130 000 yearsbp), suggesting that topographical features along the Pacific coast may maintain population separation in regions unimpacted by coastal glaciation.
Fluvial response to active extension: evidence from 3D seismic data from the Frio Formation (Oligo‐Miocene) of the Texas Gulf of Mexico Coast, USA
Authors: MAYNARD JAMES R. 
Published: April 2006

AbstractTectonic deformation of the land surface is known to influence the gradient, water and sediment discharge and the grain‐size of modern fluvial systems. Any change in these variables alters the equilibrium of a fluvial system, potentially causing a change in channel morphology. 3D seismic data from the Tertiary (Miocene) age, Upper Frio Formation, Kelsey Field, South Texas, in the US are used to examine changing fluvial channel morphology through time during a period of active growth of a rollover anticline in the hangingwall of a normal fault (the Vicksburg Fault). The studied interval varies between 22 and 47 m thick, and spans several hundred thousand years. It consists of an alternation of fluvial sandstones, overbank mudstones and coal. Seismic extractions show the evolution of sinuous fluvial channels during a phase of growth fault activity. Prior to growth, a single sinuous channel is imaged. During growth, the fluvial system became decapitated by a developing rollover anticline, and a highly sinuous drainage network formed, with frequent avulsion events, headward propagation of streams and related stream capture. Increased channel sinuosity was spatially associated with increased avulsion frequency in the area down dip to the east of the rollover anticline, more than 10 km from the active fault. More than 25 m of relative accommodation developed on the flank of the growing rollover anticline compared with on the crest. The increased channel sinuosity is interpreted as reflecting an increase in longitudinal valley slope analogous to observations made in flume experiments and modern river systems. The increase in avulsion frequency is attributed to increased aggradation as the rivers adjusted back to equilibrium grade following the increase in slope.
Genetic mating patterns studied in pools with manipulated nest site availability in two populations of Pomatoschistus minutus
Authors: Singer A. , Kvarnemo C. , Lindström K. , Svensson O. 
Published: April 2006

Abstract
Pomatoschistus minutus show paternal care in a resource defence mating system. We investigated the effect of nest-site availability on parasitic spawning. Each experimental pool contained four potentially nest-building males, four females and nests-sites in shortage (2) or excess (6). Both treatments were conducted in two populations; one with natural nest-sites in excess, one with a nest-site shortage. Microsatellite-DNA revealed that all nest-holders had fertilized most of the eggs they tended. Yet, 35% of the nests contained eggs fertilized by another male and 14.4% of the males had performed parasitic spawning. There was no site or treatment effect. Several females spawned in two nests, which coincided with parasitic spawnings, suggesting a cost to the nest-holder in terms of lost mating success. Nest-holders with and without eggs and non-nesting males all spawned parasitically, generating a significantly lower opportunity for sexual selection compared to if there had been no parasitic spawning.
Foraging Patch Selection and Departure by Non‐Omniscient Foragers: A Field Example in White‐Fronted Geese
Authors: Amano Tatsuya , Ushiyama Katsumi , Fujita Go , Higuchi Hiroyoshi 
Published: April 2006

AbstractAnimals often face great uncertainty as to the quality of foraging patches. There have been a number of theoretical studies investigating how non‐omniscient predators, i.e. predators that are unable to assess foraging patch quality prior to patch exploitation, should forage in a heterogeneous environment, but empirical studies, especially in the field, are scarce. This paper describes the way in which white‐fronted geese Anser albifrons forage on harvest remains of rice, focusing on the processes of patch selection and departure. Not only in autumn, but also in spring when rice depletion has progressed, patch rice density showed no positive effect on patch selection by geese, indicating the incapability of geese to select the most profitable patch. Instead, the geese tended to select patches with a large proportion of rice fields that were near the roost and a previously visited patch and bordered by a small number of windbreaks only. The rice consumption volume by geese increased with increasing initial rice density, while giving‐up density was independent of initial rice density and was positively correlated to the mean rice density of the habitat. This suggests that the geese could compensate their lack of information on patch quality at the moment of patch selection by leaving less profitable patches earlier. We discuss the necessity of predictive models based on random patch selection and an appropriate departure rule to explain the distribution of individuals of species with limited information on patch quality.
Measurement and modelling of residual stress effects on cracks
Authors: SHERRY A. H. , DA FONSECA J. QUINTA , GOLDTHORPE M. R. , TAYLOR K. 
Published: April 2006

ABSTRACTDefects that form by mechanisms such as fatigue and stress corrosion cracking are influenced both by external loads on engineering structures and internal, residual stresses that are generated during the manufacture and operation. This paper describes a programme of experimental and analytical work on a high‐strength, low‐toughness aluminium alloy (AL2024‐T351) to assess the influence of residual stress on crack opening displacement (COD) and crack‐driving force (CDF) for a range of fatigue crack lengths in compact tension (CT) specimens containing a mechanically induced residual stress field. Comparison of experimentally measured and numerically predicted CODs, at the mid‐plane and surface of CT specimens, show generally good agreement for cracks introduced into the finite‐element model in a progressive, element‐by‐element manner. Cracks introduced in a simultaneous manner give larger than observed CODs. The CDFs for the progressively introduced crack are always smaller than for simultaneously introduced. These results have implications for the assessment of initiation for slowly growing cracks.
Grand mal seizures: an unusual and puzzling primary presentation of ruptured hepatic hydatid cyst
Authors: MEYER PHILIPPE G. , BONNEVILLE CLAIRE , ORLIAGUET GILLES A. , DESSEMME PHILIPPE , BLAKIME PHILIPPE , CARLI PIERRE A. , REVILLON YANN 
Published: April 2006

SummaryWe report a case of hepatic hydatidosis where the first clinical manifestations, generalized seizures after minor head and abdominal trauma, and delayed anaphylaxis, made the primary diagnosis difficult. Severe anaphylaxis has been reported as initial presentation of quiescent hepatic hydatidosis. In endemic areas, the diagnosis must be carefully ruled out in patients experiencing abrupt anaphylactic shock of uncertain etiology. The occurrence of unexplained vascular collapse after minor abdominal trauma in a patient originating from an endemic area should prompt the diagnosis and urgent treatment should be initiated; firstly emergency management of the anaphylactic shock and later, surgical treatment of the cysts.
Management of right ventricular outflow tract reactivity following pulmonary valve dilatation under general anesthesia: experience of a medical mission
Authors: KHAMBATTA HOSHANG J. , VELADO MAURICIO , GAFFNEY JOSEPH W. , SCHECHTER WILLIAM S. , CASTA ALFONSO 
Published: April 2006

SummaryDuring a recent volunteer medical mission to the Dominican Republic, we administered anesthesia to a child with severe pulmonary valvular stenosis and suprasystemic right ventricular pressure. This patient underwent a balloon pulmonary valvuloplasty but then developed worsening right ventricular outflow tract obstruction that required immediate therapy to prevent a low cardiac output state. As the development of hyperdynamic right ventricular outflow tract obstruction cannot be predicted, we emphasize the need for preemptive hydration and beta‐blockade therapy prior to balloon dilatation.