bluuebunny/crossref_metadata_2025 huggingface dataset:
The Minimum Vertex Degree of a Graph on Uniform Points in [0, 1]d
Authors: Appel Martin J. B. , Russo Ralph P.
Published: April 2006

This article continues an investigation begun in [2]. A random graph Gn(x) is constructed on independent random points U1, · ··, Un distributed uniformly on [0, 1]d, d ≧ 1, in which two distinct such points are joined by an edge if the l∞-distance between them is at most some prescribed value 0 < x < 1.

Almost-sure asymptotic results are obtained for the convergence/divergence of the minimum vertex degree of the random graph, as the number n of points becomes large and the edge distance x is allowed to vary with n. The largest nearest neighbor link dn, the smallest x such that Gn(x) has no vertices of degree zero, is shown to satisfy

Series and sequence criteria on edge distances {xn} are provided which guarantee the random graph to be complete, a.s. These criteria imply a.s. limiting behavior of the diameter of the vertex set.
Near Complete Decomposability: Bounding the Error by a Stochastic Comparison Method
Authors: Truffet Laurent
Published: April 2006

An aggregation technique of ‘near complete decomposable' Markovian systems has been proposed by Courtois [3]. It is an approximate method in many cases, except for some queuing networks, so the error between the exact and the approximate solution is an important problem. We know that the error is O(ε), where ε is defined as the maximum coupling between aggregates. Some authors developed techniques to obtain a O(ε k) error with k > 1 error with k > 1, while others developed a technique called ‘bounded aggregation’. All these techniques use linear algebra tools and do not utilize the fact that the steady-state probability vector represents the distribution of a random variable. In this work we propose a stochastic approach and we give a method to obtain stochastic bounds on all possible Markovian approximations of the two main dynamics: short-term and long-term dynamics.
Comparison of differentiation estimates based on morphometric and molecular data, exemplified by various leaf shape descriptors and RAPDs in the genus Chaenomeles (Rosaceae)
Authors: Rumpunen Kimmo , Bartish Igor V.
Published: April 2006

The efficiency of classical metric descriptors (MDs), normalised elliptic Fourier coefficients (EFCs), and the power series of normalised elliptic Fourier coefficients (PEFCs) in revealing variation in leaf shape was evaluated and compared for species in the genus Chaenomeles, using canonical variates analyses (CVAs) and reclassification tests. For EFCs 30 harmonics (and for PEFCs 40 harmonics) were needed to achieve 100% correct reassignment of plants. By contrast, MDs were considerably less efficient and only 87%, 77% and 66% of the plants were correctly reassigned to species, populations, and maternal families, respectively. Furthermore, when compared with data based on molecular random amplified polymorphic DNA markers (RAPDs), PEFCs produced the most concordant data sets as revealed by cluster analyses. To obtain comparable estimates of variability and differentiation, the AMOVA approach was used both for molecular data and, as a novelty, for quantitative morphometric data. The variation was partitioned by hierarchical extraction of variance components from matrices of standardised squared Euclidean distances, and differentiation estimates were obtained as Φ­statistics. All descriptor sets partitioned the variance in a similar way. Surprisingly high correlations were found between RAPDs and elliptic Fourier transforms for the among­family estimates of variance components (RAPDs vs. PEFCs: 0.89, P = 0.003; RAPDs vs. EFCs: 0.86, P = 0.006). In contrast, only a moderate correlation was found between RAPDs and MDs (0.71, P = 0.049). This may indicate that shape per se (the size component excluded) is a less biased estimator of genetic variation than metric leaf descriptors in the genus Chaenomeles. Estimates of population differentiation based on EFCs and PEFCs were always lower than differentiation estimates based on RAPDs, whereas the differentiation estimates based on MDs were in general higher than estimates based on RAPDs, except for one species including hybrid populations.
Phylogeny of Isoëtes (Lycopsida): resolving basal relationships using rbcL sequences
Authors: Rydin Catarina , Wikström Niklas
Published: April 2006

The phylogenetic relationships of Isoëtes (Isoëtaceae) were investigated by means of a cladistic analysis using plastid rbcL sequences and a representative sample of 18 species. The analysis supports a basal split in Isoëtes separating two main groups, one including aquatic species from South America (I. bradei and I. amazonica) and West Africa (I. kersii and I. schweinfurthii), and the other including aquatic, amphibious and terrestrial species representing all major continents. Higher level relationships remain unresolved, but supported groups do conflict with previous morphology­based hypotheses. Comparatively low levels of sequence divergence indicate that the use of more rapidly evolving regions will be required to resolve higher level relationships. The phylogenetically isolated nature of Isoëtes will in such analyses make standard outgroup comparisons problematic, and results presented here will in this respect prove important by providing support for choosing among alternative rooting options.
Four succulent families and 40 million years of evolution and adaptation to xeric environments: What can stem and leaf anatomical characters tell us about their phylogeny?
Authors: Landrum James V.
Published: April 2006

Four families of the eleven or so families of Caryophyllales have been particularly successful at adapting to xeric environments: (1) ice plants (Aizoaceae), (2) cacti (Cactaceae), (3) "Old World cacti" (Didiereaceae); and (4) portulacs (Portulacaceae). Ice plants adapted to the harsh conditions of the deserts of southern Africa; many evolved leaf succulence to an extreme degree, some went underground, others lost the ability to make normal wood, and all had to adapt their reproductive strategies in pollination or seed dispersal. Cacti adapted to deserts of South, Central, and North America by losing their leaves over time and evolving various types of succulent stems. Cacti also adapted by greatly reducing the presence of vessels in their wood, evolving a novel tracheid type termed wide­band tracheids, and evolving CAM and C4 metabolisms. Plants of Didiereaceae adapted to the harsh Madagascan environment by evolving both stem and leaf succulence and the columnar stem form, but these plants maintained their normal, non­anomalous woody growth. Members of Portulacaceae evolved in many different xeric areas of southern Africa, but all evolved leaf succulence and limited stem succulence, much the same as found in Aizoaceae. Each family evolved varying strategies for living in water­stressed environments. Common themes among these distantly related plants are leaf and/or stem succulence, and anatomical and physiological adaptations.
Lines, outlines, and landmarks: morphometric analyses of leaves of Acer rubrum, Acer saccharinum (Aceraceae) and their hybrid
Authors: Jensen Richard J. , Ciofani Kristen M. , Miramontes Lydia C.
Published: April 2006

Quantitative comparisons of leaf morphology for evaluating taxonomic relationships may be conducted by traditional morphometrics, outline analyses, or geometric morphometrics. These approaches were employed for examining relationships among trees of two species of maple, Acer rubrum and A. saccharinum, and their hybrid (A. ×freemanii). Leaf samples from six hybrid trees (three each from two accessions) and 40 trees field identified as either species were pressed and dried. Leaf outline and landmark data were captured for each leaf, and linear and angular measures were derived from the landmark configurations. A vector of character means, a mean leaf outline, and a consensus landmark configuration were generated for each tree. Traditional morphological measurements, a single­parameter outline descriptor, elliptic Fourier coefficients of the outlines, and relative warp scores for the landmarks were used to depict relationships among the 46 OTUs. All three data types reveal similar patterns with respect to the two species, and the hybrids are generally intermediate between the two species. The results provide evidence of genetic segregation in one hybrid accession, that several of the field sampled trees are naturally occurring hybrids, and that relative warps analysis can reveal aspects of shape variation not detected by the other analyses.
The method of V. M. Popov for differential systems with random parameters
Authors: Tsokos Chris P.
Published: April 2006

The aim of this paper is to investigate the existence of a random solution and the stochastic absolute stability of the differential systems (1.0)–(1.1) and (1.2)–(1.3) with random parameters. These objectives are accomplished by reducing the differential systems into a stochastic integral equation of the convolution type of the form (1.4) and utilizing a generalized version of V. M. Popov's frequency response method.
The finite dam
Authors: Roes P. B. M.
Published: April 2006

Denote by X(t) the total quantity of water flowing into a weir of capacity K in the interval (0, t). Unless the weir is empty, there is a continuous release of water at unit rate; if it becomes full, the excess water overflows instantaneously.
One-to-one functions on the positive integers
Authors: Ailam Gedalia , Tata Mahabanoo N.
Published: April 2006

Let {an} be an increasing sequence of positive integers and let be the family of all functions from the positive integers into the positive integers, which satisfy

Assume that are random functions with probabilities

and for all n > 1

and 0 elsewhere, i.e., all permissible values of f, given the past, are equally likely.
Ehrenfest urn models
Authors: Karlin Samuel , McGregor James
Published: April 2006

In the Ehrenfest model with continuous time one considers two urns and N balls distributed in the urns. The system is said to be in state i if there are i balls in urn I, N − i balls in urn II. Events occur at random times and the time intervals T between successive events are independent random variables all with the same negative exponential distribution

When an event occurs a ball is chosen at random (each of the N balls has probability 1/N to be chosen), removed from its urn, and then placed in urn I with probability p, in urn II with probability q = 1 − p, (0 < p < 1).
The general N server finite queue
Authors: Kapadia Asha Seth
Published: April 2006

Kingman (1962) studied the effect of queue discipline on the mean and variance of the waiting time. He made no assumptions regarding the stochastic nature of the input and the service distributions, except that the input and service processes are independent of each other. When the following two conditions hold:

(a)

no server sits idle while there are customers waiting to be served;

(b)

the busy period is finite with probability one (i.e., the queue empties infinitely often with probability one);

he has shown that the mean waiting time is independent of the queue discipline and the variance of the waiting time is a minimum when the customers are served in order of their arrival. Conditions (a) and (b) will henceforward be called Kingman conditions and a queueing system satisfying Kingman conditions will be referred to in the text as a Kingman queue.
Biharmonic functions and Brownian motion
Authors: Helms L. L.
Published: April 2006

Let R be a bounded open subset of N-dimensional Euclidean space EN,N ≧ 1, let {xt: t ≧ 0} be a separable Brownian motion starting at a point x ɛ R, and let τ = τR be the first time the motion hits the complement of R. It is known [1] that if g is a bounded measurable function on the boundary ∂R of R, then h(x) = Ex[g(xτ)] is a harmonic function of x ɛ R which “solves” the Dirichlet problem for the boundary function g; i.e., Δh = 0 on R, where Δ is the Laplacian. In elastic plate problems, one must solve the biharmonic equation

subject to certain boundary conditions. For the more important applications, these boundary conditions involve the values of u and the normal derivative of u at points of ∂R. Even though a treatment of this Neumann type problem is not available at this time, some things can be said about biharmonic functions and their relationship to Brownian motion. We will show, in fact, that u(x)= Ex[τ(xτ)] is a biharmonic function on R which “satisfies” the boundary conditions (i) u=0 on ∂R and (ii) Δu= −2g on ∂R, provided g satisfies certain hypotheses. More generally, we will show that u(x)=Ex[Δkg(XΔ)] is polyharmonic of order k + 1 on R (i.e., Δk + 1u = Δ(Δku) = 0 on R) and that it satisfies certain boundary conditions. A treatment of the special case g ≡ 1 on ∂R can be found in [3].
An iterated logarithm law for maxima of nonstationary Gaussian processes
Authors: Deo Chandrakant M.
Published: April 2006

An iterated logarithm type theorem is obtained for maxima of nonstationary discrete-parameter Gaussian processes.
The robustness of positive recurrence and recurrence of Markov chains under perturbations of the transition probabilities
Authors: Tweedie Richard L.
Published: April 2006

In many Markov chain models, the immediate characteristic of importance is the positive recurrence of the chain. In this note we investigate whether positivity, and also recurrence, are robust properties of Markov chains when the transition laws are perturbed. The chains we consider are on a fairly general state space : when specialised to a countable space, our results are essentially that, if the transition matrices of two irreducible chains coincide on all but a finite number of columns, then positivity of one implies positivity of both; whilst if they coincide on all but a finite number of rows and columns, recurrence of one implies recurrence of both. Examples are given to show that these results (and their general analogues) cannot in general be strengthened.
Anisotropically random mosaics
Authors: Moore Marc
Published: April 2006

The concept of isotropically random mosaic introduced by Pielou, is recalled. The notion of anisotropically random mosaic with respect to a point is defined. An example is given.
Traffic intersection control and zero-switch queues under conditions of Markov chain dependence input
Authors: Lehoczky J. P.
Published: April 2006

A model for a vehicle controlled intersection based on a zero-switch queueing system is introduced and analyzed under Markov chain dependence input. Conditions for asymptotic stability are derived. Under these conditions the moments of the cycle lengths are derived. The expected area beneath the sample paths given by the queue sizes is computed. This area represents total delay to all cars, and is a measure of the effectiveness of the control device.
The expected first-passage time for a sufficient statistic arising in the Poisson disorder problem
Authors: Wickwire K.
Published: April 2006

In the Poisson disorder problem the probability that the parameter of a Poisson process y, has increased by a constant amount, given observations of ys, s ≦ t, is a Markov process of mixed type with jumps of variable (state-dependent) magnitude superimposed upon a drift which satisfies an ordinary differential equation. Using a likelihood-ratio transformation, one can reduce the backward equation satisfied by the expected first-passage time to a constant level for the mixed process to a differential-difference equation with a constant retardation. We discuss a method for solving this equation and present some numerical results on its solution. The accuracy of some approximations which are easier to calculate is investigated.
A queuing-theoretic anomaly
Authors: Burke P. J.
Published: April 2006

The equilibrium delay distribution for a system with finite-source input, constant service time, and s > 1 servers, as determined by simulation, showed the existence of values of t such that the probability of delay greater than t is a non-monotone function of the input intensity. Since repeated efforts to remove this counter-intuitive result by debugging failed, a simple case was attacked by analytical and numerical methods; and the same anomaly was revealed. The method of analysis is described and an explanation of the result is offered.
On a characterization of gamma distributions via exponential mixtures
Authors: Bhattacharjee Manish C.
Published: April 2006

A new and simpler proof of Morrison's result that within exponential mixtures only IFR gamma mixing produces linearly increasing mean residual life functions is given. A parallel and new characterization of the DFR gamma laws follows as a consequence. The method of proof used suggests a general result on the infinite divisibility of the mixing distributions in exponential mixtures.
Gaussian families and a theorem on patterned matrices
Authors: Barrett Wayne W. , Feinsilver Philip J.
Published: April 2006

In this paper we use the properties of the covariance matrix of a Gaussian Markovian family to give a probabilistic proof of a theorem about inverses of tridiagonal matrices.
A state-dependent lifetime process of individuals subject to external perturbations
Authors: Mergenthaler Wolfgang
Published: April 2006

We consider an individual which ultimately dies or divides, and whose state is subject to drift and jumps caused by external perturbations. The mortality and division rates being state-dependent, the present paper deals with the time-dependent distribution of the individual's position in the state-space and with its lifetime distribution. The results are applied to a model of a biological cell which is exposed to ionizing radiation. Under certain conditions on the parameters of the type of perturbation one can show that the division probability decreases and the mean regeneration time increases with increasing frequency and ‘effect' of the perturbations.
A comparison criterion for explosions in point processes
Authors: Haezendonck J. , de Vylder F.
Published: April 2006

It is proved that under certain conditions the probability of explosion of a first point process is not larger than the probability of explosion of a second point process if the intensities of both processes fulfil the same inequality.
A unified approach to limit theorems for urn models
Authors: Holst Lars
Published: April 2006

An urn contains A balls of each of N colours. At random n balls are drawn in succession without replacement, with replacement or with replacement together with S new balls of the same colour. Let Xk be the number of drawn balls having colour k, k = 1, …, N. For a given function f the characteristic function of the random variable ZM = f(X1)+ … + f(XM), M ≦ N, is derived. A limit theorem for ZM when M, N, n → ∞is proved by a general method. The theorem covers many special cases discussed separately in the literature. As applications of the theorem limit distributions are obtained for some occupancy problems and for dispersion statistics for the binomial, Poisson and negative-binomial distribution.
Limit theorems for sums of a sequence of random variables defined on a Markov chain
Authors: Wolfson David B.
Published: April 2006

Let {(Jn, Xn), n ≧ 0} be the standard J–X process of Markov renewal theory. Suppose {Jn, n ≧ 0} is irreducible, aperiodic and positive recurrent. It is shown using the strong mixing condition, that if converges in distribution, where an, bn > 0 (bn → ∞) are real constants, then the limit law F must be stable. Suppose Q(x) = {PijHi(x)} is the semi-Markov matrix of {(JnXn), n ≧ 0}. Then the n-fold convolution, Q∗n(bnx + anbn), converges in distribution to F(x)Π if and only if converges in distribution to F. Π is the matrix of stationary transition probabilities of {Jn, n ≧ 0}. Sufficient conditions on the Hi's are given for the convergence of the sequence of semi-Markov matrices to F(x)Π, where F is stable.
Weak lumpability in finite Markov chains
Authors: Abdel-moneim Atef M. , Leysieffer Frederick W.
Published: April 2006

Criteria are given to determine whether a given finite Markov chain can be lumped weakly with respect to a given partition of its state space. These conditions are given in terms of solution classes of systems of linear equations associated with the transition probability matrix of the Markov chain and the given partition.
A transformation for normal extremes
Authors: Daniels H. E.
Published: April 2006

A transformation is introduced to stabilize the variance of the largest value in a sample from a normal distribution. The transformed distribution is found to approximate closely to the limiting Gumbel form for all sample sizes. The practical implications of the result are discussed.
Some limit theorems for clustered occupancy models
Authors: Ammann Larry P.
Published: April 2006

Most generalizations of the classical occupancy model involve non-homogeneous shot assignment probabilities, but retain the independence of the individual shot assignments. Hence, these models are associated with non-homogeneous Poisson processes. The present article discusses a generalization in which the shot assignments are not independent, but which result in clustering of the shots. Conditions are given under which this clustered occupancy model converges to a Poisson cluster process. Limiting distributions for the number of empty cells are obtained for various allocation intensities when the total number of shots is deterministic as well as random. In particular, it is shown that when the allocation is sparse, then the limiting distribution of the number of empty cells is compound Poisson.
Exact and limiting distribution of sustained maxima
Authors: Canfield E. R. , McCormick W. P.
Published: April 2006

Define a random variable

We refer to Yn as a sustained maximum. Under the assumption that the Xi's are i.i.d. the exact distribution of Yn is obtained. Under certain conditions on the underlying distribution F we obtain weak limit results for the Yn as well. Also a combinatorial extreme-value problem is solved.
Consistency for the least squares estimator in a transfer function model
Authors: Solo Victor
Published: April 2006

The consistency is developed under mild conditions for the least squares estimator of the parameters of a transfer function time series model.
The asymptotic behavior o queues with time-varying arrival rates
Authors: Heyman Daniel P. , Whitt Ward
Published: April 2006

This paper discusses the asymptotic behavior of the Mt/G/c queue having a Poisson arrival process with a general deterministic intensity. Since traditional equilibrium does not always exist, other notions of asymptotic stability are introduced and investigated. For the periodic case, limit theorems are proved complementing Harrison and Lemoine (1977) and Lemoine (1981).
The non-ergodic Jackson network
Authors: Goodman Jonathan B. , Massey William A.
Published: April 2006

We generalize Jackson's theorem to the non-ergodic case. Here, despite the fact that the entire Jackson network will not achieve steady state, it is still possible to determine the maximal subnetwork that does. We do so by formulating and algorithmically solving a new non-linear throughput equation. These results, together with the ergodic results and the ones for closed networks, completely characterize the large-time behavior of any Jackson network.
Non-standard insensitivity
Authors: Henderson W.
Published: April 2006

The paper takes a closer look at some insensitivity results which are not contained in the class of insensitive generalised semi-Markov schemes. Based on a study of a special insensitive queue, a conjecture is proposed which covers all known results on insensitive equilibrium distributions. When insensitive events are also included, a study of the G/G/1 queue shows that the conjecture does not always hold.
A functional form for a particular coefficient of ergodicity
Authors: Tan Choon-Peng
Published: April 2006

Seneta, in a recent paper, presented a general treatment of the concept of ‘coefficient of ergodicity', τ (P), for a finite stochastic matrix P. In this paper, a functional form for τ∞(P) in terms of the attributes of P is determined. It is shown that, by increasing the dimension of P, τ∞(Ρ) can assume any large value. In view of this, τ∞ will be practically useful only in the case τ∞(P) ≦ τ1(P), where τ1(P) is the well-known Dobrushin or delta coefficient.
On the possible form of size distributions for Gibbsian processes of mutually non-intersecting balls
Authors: Mase Shigeru
Published: April 2006

We construct a model of mutually non-intersecting balls using a generalized notion of Gibbsian processes and characterize its size, i.e. radius, distribution. The explicit form of this distribution is given in the one-dimensional case, that is, mutually non-intersecting segment processes on the line.
Stationary Poisson departure processes from non-stationary queues
Authors: Foley Robert D.
Published: April 2006

We present some non-stationary infinite-server queueing systems with stationary Poisson departure processes. In Foley (1982), it was shown that the departure process from the Mt/Gt/∞ queue was a Poisson process, possibly non-stationary. The Mt/Gt/∞ queue is an infinite-server queue with a stationary or non-stationary Poisson arrival process and a general server in which the service time of a customer may depend upon the customer's arrival time. Mirasol (1963) pointed out that the departure process from the M/G/∞ queue is a stationary Poisson process. The question arose whether there are any other Mt/Gt/∞ queueing systems with stationary Poisson departure processes. For example, if the arrival rate is periodic, is it possible to select the service-time distribution functions to fluctuate in order to compensate for the fluctuations of the arrival rate? In this situation and in more general situations, it is possible to select the server such that the system yields a stationary Poisson departure process.
Identifiability of time series models with errors in variables
Authors: Solo Victor
Published: April 2006

Straightforward derivations are provided for some identifiability results for time series models with errors in variables.
Limit motion of an Ornstein–Uhlenbeck particle on the equilibrium manifold of a force field
Authors: Calzolari Antonella , Marchetti Federico
Published: April 2006

In this paper we consider a position–velocity Ornstein-Uhlenbeck process in an external gradient force field pushing it toward a smoothly imbedded submanifold of . The force is chosen so that is asymptotically stable for the associated deterministic flow. We examine the asymptotic behavior of the system when the force intensity diverges together with the diffusion and the damping coefficients, with appropriate speed. We prove that, under some natural conditions on the initial data, the sequence of position processes is relatively compact, any limit process is constrained on , and satisfies an explicit stochastic differential equation which, for compact , has a unique solution.
On unbounded hazard rates for smoothed perturbation analysis
Authors: Fu Michael C. , Hu Jian-Qiang
Published: April 2006

Many applications of smoothed perturbation analysis lead to estimators with hazard rate functions of underlying distributions. A key assumption used in proving unbiasedness of the resulting estimator is that the hazard rate function be bounded, a restrictive assumption which excludes all distributions with finite support. Here, we prove through a simple example that this assumption can in fact be removed.
Recurring-with-carry sequences
Authors: Koç Cemal
Published: April 2006

In this note we introduce recurring-with-carry sequences which generalize add-with-carry and subtract-with-borrow sequences introduced in [1], and describe periods of admissible recurring-with-carry sequences which include add-with-carry and subtract-with-borrow sequences with a few exceptions.
Problèmes de premier passage résolubles par la méthode de séparation des variables
Authors: Lefebvre Mario
Published: April 2006

In this paper, bidimensional stochastic processes defined by ax(t) = y(t)dt and dy(t) = m(y)dt + [2v(y)]1/2dW(t), where W(t) is a standard Brownian motion, are considered. In the first section, results are obtained that allow us to characterize the moment-generating function of first-passage times for processes of this type. In Sections 2 and 5, functions are computed, first by fixing the values of the infinitesimal parameters m(y) and v(y) then by the boundary of the stopping region.
Pathological behaviour in loss networks
Authors: Hunt P. J.
Published: April 2006

Hunt and Kurtz [9] consider a loss network as the number of circuits and the offered traffics become large. They prove a functional law of large numbers for such a network and illustrate their results with some simple examples. In this paper we apply their results to slightly more complicated examples to illustrate other, and sometimes surprising, behaviour of the loss networks in heavy traffic. The networks we consider operate under somewhat unusual routing rules but this is to enable us to produce the behaviour in networks with only a few links. In larger, real-world networks it is likely that much more ‘natural' and intuitively appealing routing rules could produce similar undesirable behaviour.
Comparison of system reliability functions under laboratory and common operating environments
Authors: Woodham Sara-Anne , Richards Donald St. P.
Published: April 2006

We compare R1(t), the reliability function of a redundant m-of-n system operating within the laboratory, with RD(t), the reliability function of the same system operating subject to environmental effects. Within the laboratory, all component lifetimes are independent and identically distributed according to G(α + 1, λ), a gamma distribution with index α + 1 and scale λ. Outside the laboratory, we adopt the model of Lindley and Singpurwalla (J. Appl. Prob. 23 (1986), 418-431) and assume that, conditional on a positive random variable η which models the effect of the common environment, all component lifetimes are independent and identically distributed according to G(α + 1, λη). When α is a non-negative integer we prove that for RD(t) to underestimate (resp. overestimate) R1(t) for all t sufficiently close to zero, it is necessary and sufficient that E(η(n-m + 1)(α+1)) > 1 (resp. E(η(n-m + 1)(α+1)) < 1). In the case in which n = 2, m= 1 and α = 0 we obtain a special case of a result of Currit and Singpurwalla (J. Appl. Prob. 26 (1988), 763-771). As an application, we obtain a necessary and sufficient condition under which RD(t) initially understimates (or overestimates) R1(t) when η follows a gamma or an inverse Gaussian distribution.
Adrenal responsiveness of reindeer (Rangifer tarandus tarandus) to intravenously administered ACTH
Authors: Säkkinen H. , Tornberg J. , Goddard P. J. , Eloranta E. , Dahl E. , Ropstad E. , Saarela S.
Published: April 2006

Plasma cortisol concentrations were determined from the blood of eight mature female reindeer (Rangifer tarandus tarandus) after an intravenous injection of either saline (control) or 100, 250 or 500 μg of synthetic ACTH. Blood samples were collected at 0, 2, 4, 6, 8, 10, 15, 20, 25, 30, 45, 60, 75, 90, 120, 150, and 180 min after the injections. The aims were to determine the appropriate dose of ACTH for adrenal stimulation tests, to define the dose level of ACTH which elicited a maximal cortisol response and to describe the range of blood cortisol concentrations for reference when evaluating the stress responses of reindeer.

The mean plasma cortisol concentrations (s.e.) at the zero sample times (t0) of the control and the ACTH treatments varied between 93·4 (11·8) and 132·5 (18·1) nmol/l. The total plasma cortisol response (area under curve, AUC, nmol/l × min) increased with increasing dose of ACTH (P < 0·001). The AUC of the control treatment was significantly smaller than of the ACTH treatments (P < 0·001). The highest dose of ACTH (500 μg) gave a significantly bigger AUC than the lowest dose (100 μg) (P = 0·008). The maximal plasma cortisol concentrations (CMAX) were achieved within 60 min of the ACTH injections. The ranges of individual CMAX were 59·0 to 136·8 nmol/l for the control treatment, and 110·0 to 252·0, 152·0 to 247·5 and 135·1 to 257·1 nmol/l for 100, 250 and 500 μg ACTH, respectively. The difference in CMAX was significant between the control treatment and the ACTH treatments (P < 0·001) but not between the different doses of ACTH. The plasma cortisol concentrations at the end of the observation period at t180 were not significantly affected by the ACTH treatment (P > 0·05).

In conclusion, the 100-μg dose of ACTH was sufficient to produce a significant cortisol response compared with the control treatment. Increasing the dose did not increase the maximal response, but tended to elongate the response profile. The blood sampling frequency used in the study was found suitable for detection of the cortisol response in reindeer.
Effect of herbage allowance and concentrate food level offered to ewes in late pregnancy on ewe and lamb performance
Authors: Dawson L. E. R. , Carson A. F. , Kilpatrick D. J. , Laidlaw A. S.
Published: April 2006

Two experiments were undertaken to investigate the effect of herbage allowance and concentrate food level offered to twin-bearing ewes in the last 6 weeks of pregnancy on ewe and lamb performance. In each study, 96 twin-bearing Greyface (Border Leicester × Scottish Blackface), Rouge × Greyface and Texel × Greyface ewes were used. In experiment 1, the ewes were allocated to eight treatments consisting of two herbage allowances (1·3 and 2·6 kg herbage dry matter per ewe per day) and four concentrate food levels ranging from zero to 1000 g per day. In experiment 2, ewes were offered four herbage allowances (1·3, 1·75, 2·2 and 2·6 kg herbage dry matter per ewe per day) and zero or 500 g concentrates per day. In experiment 1, herbage allowance and concentrate food level had no significant effect on lamb birth weight, lamb mortality or lamb performance up to weaning. Herbage dry matter intake decreased linearly with increasing concentrate food level with a substitution rate of 18 g of herbage dry matter per 100 g concentrate food level. In experiment 2, lamb birth weight increased with increasing herbage allowance (P< 0·01) and with increasing concentrate food level (P< 0·01). However, lamb performance to weaning was unaffected by late pregnancy nutrition. The satisfactory levels of performance obtained with ewes offered grass-only diets in late pregnancy indicates that grazed grass is a high nutritive value food for twin-bearing ewes in late pregnancy.
Assessing cubicle dimensions for finishing bulls based on animal behaviour and cleanliness
Authors: Gygax L. , Westerath H. Schulze , Kuhlicke J. , Wechsler B. , Mayer C.
Published: April 2006

Finishing bulls need increasingly large cubicles throughout their growth, and optimal cubicle dimensions may differ from those used for dairy cows. The space requirements of finishing bulls was investigated by observing standing-up and lying-down behaviour, lying duration and number of lying bouts, as well as the cleanliness of cubicles and animals before and after increasing cubicle size at four different points in time. Lying area in the cubicles measured 120 × 70 cm at the start and 185 × 110 cm at the end of the finishing period (approx. at 160 and 550 kg, respectively). Twenty animals kept in four groups were observed at weights of approximately 220, 330, 380 and 500 kg before and after cubicle dimensions were increased. The proportion of standing-up events with more than one head lunge decreased with enlargement of the cubicles (P = 0·01). As cubicle size increased, bulls hit the partition rails less on standing up, except at 220 kg weight where the pattern was inverted (interaction: P = 0·001). Partitions were also hit less on lying down as cubicle size increased, except at 220 kg weight with an inverse pattern (interaction: P = 0·01). The number of exploratory head sweeps before lying down did not change with cubicle enlargement (P > 0·5). Bulls slipped more often with cubicle enlargement, except at 380 kg where the difference was inverted (interaction: P = 0·03). They never fell and never turned around in the cubicles. In general, both animals and cubicles were very clean. On average, lying duration decreased (P < 0·01) while the number of lying bouts tended to increase (P = 0·052) with enlargement of the cubicles but the absolute differences were small. Consequently at each point in time, the smaller cubicles still seemed to provide sufficient lying space for the bulls. If the impacts with the partitions were minor and did not represent a serious welfare concern, as suggested by qualitative observations, the cubicle dimensions used could be considered suitable for housing the type of finishing bulls used in this study.
Effects of supplementation and stocking rate on body condition and production parameters of multiparous beef cows
Authors: Renquist B. J. , Oltjen J. W. , Sainz R. D. , Connor J. M. , Calvert C. C.
Published: April 2006

Fall-calving multiparous Angus × Hereford cows 3 to 10 years of age were stratified by age in a three by two factorial treatment arrangement to evaluate the efficacy of modifying stocking rate and supplementation strategy to manage cow body condition and production parameters over a 5-year study. Efficacy was evaluated quarterly in association with calving, breeding, weaning, and mid way between weaning and calving (i.e. in August). Three protein supplementation strategies (none, standard, strategic) were imposed across both a moderate (0·3 cows per ha) and a high (0·4 cows per ha) stocking rate. In the strategically supplemented group, protein supplement was provided to cows with a body condition score <5·5 at the quarterly evaluations. There was an effect of supplementation on pregnancy rate, which in combination with previously established culling practices resulted in different age profiles amongst supplementation strategies in years 2 to 5 (P < 0·01). Two statistical analyses were therefore conducted to dissociate the confounding effects of supplementation strategy and age. One model included the effect of stocking rate, supplementation strategy, production year, and all interactions; the second included the addition of age and its interactive effects. Stocking rate and supplementation strategy affected pregnancy rate in each of the models (P = 0·003 and P = 0·10, respectively). Standard, non-supplemented and strategically supplemented animals had estimated pregnancy rates of 0·83, 0·76, and 0·79, respectively (P = 0·10). The effects of nutrition on both calving interval and birth weight were independent of the model employed. Animals that were not supplemented had extended calving intervals (P = 0·06), but there was no effect of stocking rate (P > 0·10). Birth weight was not affected by supplementation strategy or stocking rate (P > 0·10). The lower 205-day weights of calves on a heavy compared with moderate stocking rate was independent of age (P = 0·02). However, the increased 205-day weight of calves born to strategically supplemented cows compared with those born to unsupplemented cows was only evident when data were not corrected for differences in age among groups (P = 0·03). Likewise, analyses of cow condition parameters using models without and with age resulted in different interpretations. These results suggest that strategic and standard supplementation result in similar animal performance and that the improvement in herd productivity associated with altering stocking rate and supplementation may partially be due to altered herd age dynamics.
Investigating environmental variation and landscape characteristics of an urban–rural gradient using woodland carabid assemblages
Authors: Sadler J. P. , Small E. C. , Fiszpan H. , Telfer M. G. , Niemelä J.
Published: April 2006

Aim To investigate environmental variation and associated assemblage changes of carabid beetles along an urban–rural gradient.

Location ‘Quercus–Acer’ (oak–sycamore) woodlands in the city of Birmingham, UK.

Methods We collected carabid data using pitfall traps on 12 sites in the city. The traps were run from April–September in 2000, and we collected environmental data on 24 individual variables associated with the individual sites and their landscape context. Changes in carabid assemblages were analysed using repeat measuresanovaand the environment–species relationships with a Redundancy Analyses (RDA) and Generalized Linear Modelling (GLM).

Results We found that: (1) species richness and diversity were lower in the urban and suburban zone and higher in the rural zone; (2) Berger Parker dominance index was higher in the urban and suburban zones; (3) the number of woodland and woodland associated species was significantly higher at the rural end of the gradient; (4) the number of short‐winged (brachypterous) species was highest in the rural zone and decreased towards the urban woodlands, whereas the long‐winged species were more abundant in suburban woodlands; (5) the median weight length (WML) of the assemblage declined along the gradient from the rural to the urban zone, as did the number of large species; and (6) five of the 24 environmental variables showed a significant relationship with variation in the carabid assemblage. At site level the carabid assemblages were related to the level of site disturbance and soil penetrability, whereas site size and amount of woodland and urban land within 5 km of the site were important at a larger landscape scale.

Main conclusions The results suggest that urbanization has a deleterious impact on carabid assemblages, causing a reduction in species richness from the rural fringe to the centre of the city. Changes in assemblage structure were related to woodland fragmentation, which led to variations in woodland size, woodland location and site disturbance due to trampling. Large, flightless and specialist woodland species are more susceptible to changes associated with urbanization, presumably due to their longer life spans, lower reproductive rates, more specialized niches and more limited dispersal potential.
Geographical expansion and increased prevalence of common species in avian assemblages: implications for large‐scale patterns of species richness
Authors: La Sorte Frank A.
Published: April 2006

Aim The assumption that ecological patterns at large spatial scales originate exclusively from non‐anthropogenic processes is growing more questionable with the increasing domination of the biosphere by humans. Because common and rare species are known to respond differently to anthropogenic activities at local scales these differential responses could, over time, be reflected in distributional patterns of species richness at larger spatial scales. This work tests the hypothesis that modern processes have played a role in shaping these patterns, by examining recent changes in the structure and composition of assemblages of breeding avifauna over a large geographical extent.

Location The portion of North America containing the contiguous United States and southern Canada.

Methods Changes in the geographical range structure of breeding avifauna in North America from 1968 to 2003 were analysed in regions containing historically moderate levels of anthropogenic activities. Two geographical measures, extent of occurrence and area of occupancy, were used to identify the level of rarity or commonality of individual species and to estimate, based on a vector analysis, patterns of change in geographical range structure for individual species and avian assemblages.

Results More species experienced patterns of geographical range expansion (51%) than contraction (28%). The majority of avian assemblages (43%) displayed patterns of geographical range expansion: common species increased in number and proportion (6%) in association with reciprocal losses in rare and moderately rare species, resulting in a constant level of species richness. The minority of avian assemblages (21%) displayed patterns of geographical range contraction: gains occurred for common species as well as for rare and moderately rare species, resulting in substantial increases in species richness and a decline in the proportion of common species (4%). The remaining avian assemblages presented equivocal patterns characterized by gains in the number and proportion (2%) of common species and gains in species richness.

Main conclusions Modern processes have played a role in shaping the distribution patterns of species richness at large spatial scales based on the composition of common and rare species. This suggests that anthropogenic activities cannot be ignored as a possible causal factor when considering ecological patterns at large spatial scales.
Assessing the effects of stimulation versus microswitch‐based programmes on indices of happiness of students with multiple disabilities
Authors: Lancioni G. E. , Singh N. N. , O’Reilly M. F. , Oliva D. , Smaldone A. , Tota A. , Martielli G. , Stasolla F. , Pontiggia G. , Groeneweg J.
Published: April 2006

Background  Stimulation and microswitch‐based programmes are considered main strategies to promote indices of happiness in students with multiple disabilities. However, only limited attempts have been made to assess the relative effects of the two programmes. This study conducted such an assessment with seven students with multiple disabilities.

Methods  The first four phases of the study served to: (1) provide the students with a systematic exposure to each of the programmes; and (2) measure the programmes’ effects on indices of happiness by comparing them with baseline levels. The fifth phase served to compare the programmes with each other.

Results  The first four phases of the study showed that the microswitch‐based programme produced a significant increase in indices of happiness for all seven students, and the stimulation programme produced a significant increase for six students. During the fifth phase of the study (i.e. when the two programmes were alternated), the microswitch‐based programme promoted significantly higher indices of happiness than the stimulation programme for four of the seven students.

Conclusions  Microswitch‐based programmes might be deemed preferable to stimulation programmes because they can promote higher or comparable indices of happiness while promoting the acquisition of adaptive responses and self‐determination.
Heterozygote excess in a self‐incompatible and partially clonal forest tree species —Prunus avium L.
Authors: STOECKEL SOLENN , GRANGE JÉRÔME , FERNÁNDEZ‐MANJARRES JUAN F. , BILGER ISABELLE , FRASCARIA‐LACOSTE NATHALIE , MARIETTE STÉPHANIE
Published: April 2006

Wild cherry (Prunus avium L.), a partially asexual self‐incompatible forest tree, shows heterozygote excess, which is a poorly studied phenomenon. In three natural populations, we found significant heterozygote excess at almost all investigated loci (eight microsatellites and markers for the self‐incompatibility locus). We examined four hypotheses to account for this observed heterozygote excess. First, negative FIS can result from a lack of selfed progeny in small populations of outcrossing species. A second explanation for negative FIS is selection during the life cycle of the most heterozygous individuals. A third explanation is negative assortative mating when reproduction occurs between individuals bearing phenotypes more dissimilar than by chance. The last explanation for negative FIS relies on asexual reproduction. Expectations for each hypothesis were tested using empirical data. Patterns of FIS differed among loci. Nevertheless, our experimental results did not confirm the small sample size hypothesis. Although one locus is probably under a hitch‐hiking effect from the SI locus, we rejected the effect of the self‐incompatibility locus for the genome as a whole. Similarly, although one locus showed a clear pattern consistent with the selection of heterozygous individuals, the heterosis effect over the whole genome was rejected. Finally, our results revealed that clonality probably explains significant negative FIS in wild cherry populations when considering all individuals. More theoretical effort is needed to develop expectations and hypotheses, and test them in the case of species combining self‐incompatibility and partially asexual reproduction.