bluuebunny/crossref_metadata_2025_split huggingface dataset:
Ultrastructural Study of the Filum Terminale and Its Elastic Fibers
Authors: Fontes Ricardo B.V. , Saad Felippe , Soares Matheus S. , de Oliveira Flavia , Pinto Fernando C.G. , Liberti Edson A. 
Published: April 2006

Abstract

OBJECTIVE:
The filum terminale (FT) is a fibrovascular band involved in the pathophysiology of tethered cord syndrome (TCS). Its morphological and ultrastructural properties remain largely unknown even though they are thought to play a role in the generation of TCS in adult patients with normal level conus medullaris.

MATERIALS AND METHODS:
Twenty fresh adult human cadavers had their fila measured and removed. Transversal and longitudinal sections of the proximal, middle, and distal thirds of FT were submitted to light microscopy analysis with four different techniques. Five fila were selected for longitudinal and transversal scanning electron microscopy analysis.

RESULTS:
The bulk of the FT is composed of 5- to 20-μm thick longitudinal bundles of Type 1 collagen separated by 3- to 10-μm intervals, although capillaries and other elements may be present. A delicate (0.05–1.5 μm) meshwork of predominantly Type 3 collagen transversal fibers connects these bundles. Abundant longitudinally oriented elastic and elaunin fibers are found inside collagen bundles. A complex tridimensional structure is evidenced on electron microscopy.

CONCLUSION:
The longitudinal arrangement of collagen bundles and the impressive amount of elastic and elaunin fibers should elicit considerable elastic properties to the FT. An altered elasticity mechanism has been proposed for TCS; further studies are needed with TCS patients to define whether the collagen structure, Type 1/Type 3 proportion, or elastic fiber content are altered, which could lead to new histopathological definitions of TCS, helping neurosurgeons in the difficult management of TCS patients with normal level conus medullaris.
Diffusion approximations of Markov chains with two time scales and applications to population genetics, II
Authors: Ethier S. N. , Nagylaki Thomas 
Published: April 2006

ForN =1, 2, …, let {(XN(k),YN(k)),k =0, 1, …} be a time-homogeneous Markov chain in. Suppose that, asymptotically asN → ∞, the ‘infinitesimal' covariances and means ofXN([·/εN]) areaij(x, y) andbi(x, y), and those ofYN([·/δN]) are 0 andcl(x, y). Assumeand limN→∞εN/δN= 0. Then, under a global asymptotic stability condition ondy/dt = c(x, y) or a related difference equation (and under some technical conditions), it is shown that (i)XN([·/εN]) converges weakly to a diffusion process with coefficientsaij(x, 0) andbi(x, 0) and (ii)YN([t/εN]) → 0 in probability for everyt> 0. The assumption in Ethier and Nagylaki (1980) that the processes are uniformly bounded is removed here.The results are used to establish diffusion approximations of multiallelic one-locus stochastic models for mutation, selection, and random genetic drift in a finite, panmictic, diploid population. The emphasis is on rare, severely deleterious alleles. Models with multinomial sampling of genotypes in the monoecious, dioecious autosomal, andX-linked cases are analyzed, and an explicit formula for the stationary distribution of allelic frequencies is obtained.
Phase transition in one-dimensional random walk with partially reflecting boundaries
Authors: Percus Ora E. 
Published: April 2006

We consider an asymmetric random walk, with one or two boundaries, on a one-dimensional lattice. At the boundaries, the walker is either absorbed (with probability 1–ρ) or reflects back to the system (with probability p).The probability distribution (Pn(m)) of being at position m after n steps is obtained, as well as the mean number of steps before absorption. In the one-boundary case, several qualitatively different asymptotic forms of Pn(m) result, depending on the relationship between transition probability and the reflection probability.
Moments for first-passage and last-exit times, the minimum, and related quantities for random walks with positive drift
Authors: Janson Svante 
Published: April 2006

Consider the sequence of partial sums of a sequence of i.i.d. random variables with positive expectation.We study various random quantities defined by the sequence of partial sums, e.g. the time at which the first or last crossing of a given level occurs, the value of the partial sum immediately before or after the crossing, the minimum of all partial sums. Necessary and sufficient conditions are given for the existence of moments of these quantities.
The policy which maximises long-term survival of an animal faced with the risks of starvation and predation
Authors: McNamara J. M. 
Published: April 2006

This paper presents a simple model of the decision problems which face many animals in the wild. Animals have an upper limit to the amount of energy reserves which can be stored as body fat. They constantly use energy and find food as a stochastic process. Death occurs if energy reserves fall to zero or if the animal is taken by a predator. Typically animals have a range of behavioural options which differ in the distribution of food gained and in the associated predation risk. There is often a trade-off between starvation and predation in that animals have to expose themselves to higher predation risks in order to gain more food.The above situation is modelled as a finite-state, finite-time-horizon Markov decision problem. The policy which maximises long-term survival probability is characterised. As special cases two trade-offs are analysed. It is shown that an animal should take fewer risks in terms of predation as its reserves increase, and that an animal should reduce the variability of its food supply at the expense of its mean gain as its reserves increase.
Stochastic comparisons for queueing models via random sums and intervals
Authors: Jean-Marie Alain , Liu Zhen 
Published: April 2006

We consider the relationships among the stochastic ordering of random variables, of their random partial sums, and of the number of events of a point process in random intervals. Two types of result are obtained. Firstly, conditions are given under which a stochastic ordering between sequences of random variables is inherited by (vectors of) random partial sums of these variables. These results extend and generalize theorems known in the literature. Secondly, for the strong, (increasing) convex and (increasing) concave stochastic orderings, conditions are provided under which the numbers of events of a given point process in two ordered random intervals are also ordered.These results are applied to some comparison problems in queueing systems. It is shown that if the service times in two M/GI/1 systems are compared in the sense of the strong stochastic ordering, or the (increasing) convex or (increasing) concave ordering, then the busy periods are compared for the same ordering. Stochastic bounds in the sense of increasing convex ordering on waiting times and on response times are provided for queues with bulk arrivals. The cyclic and Bernoulli policies for customer allocation to parallel queues are compared in the transient regime using the increasing convex ordering. Comparisons for the five above orderings are established for the cycle times in polling systems.
On the comparison of the distribution of the supremum of random fields represented by stochastic integrals
Authors: Orsingher Enzo , Bassan Bruno 
Published: April 2006

In this paper we compare the distribution of the supremum of the Gaussian random fields Z(P) = ∫CpG(P, P′) dW(P′) and U(P) = ∫CpdW(P'), where CP are circles of fixed radius, dW is a white noise field and G are special deterministic response functions.The results obtained permit us to establish upper bounds for the distribution of the supremum of Z(P) by applying some well-known inequalities on U(P).The comparison of the suprema is carried out also, when CP = ℝ2, between fields with different response functions.
A Remark on the Van Lieshout and Baddeley J-Function for Point Processes
Authors: Bedford T. , Van Den Berg J. 
Published: April 2006

The empty space function of a stationary point process in ℝd is the function that assigns to each r, r > 0, the probability that there is no point within distance r of O. In a recent paper Van Lieshout and Baddeley study the so-called J-function, which is defined as the ratio of the empty space function of a stationary point process and that of its corresponding reduced Palm process. They advocate the use of the J-function as a characterization of the type of spatial interaction.Therefore it is natural to ask whether J ≡ 1 implies that the point process is Poisson. We restrict our analysis to the one-dimensional case and show that a classical construction by Szász provides an immediate counterexample. In this example the interpoint distances are still exponentially distributed. This raises the question whether it is possible to have J ≡ 1 but non-exponentially distributed interpoint distances. We construct a point process with J ≡ 1 but where the interpoint distances are bounded.
A limit theorem for certain disordered random systems
Authors: Ding Xinhong 
Published: April 2006

Many disordered random systems in applications can be described by N randomly coupled Ito stochastic differential equations in :
where is a sequence of independent copies of the one-dimensional Brownian motion W and ( is a sequence of independent copies of the ℝp-valued random vector ξ. We show that under suitable conditions on the functions b, σ, K and Φ the dynamical behaviour of this system in the N → (limit can be described by the non-linear stochastic differential equation where P(t, dx dy) is the joint probability law of ξ and X(t).
Bisexual branching diffusions
Authors: Mytnik Leonid , Adler Robert J. 
Published: April 2006

We study the limiting behaviour of large systems of two types of Brownian particles undergoing bisexual branching. Particles of each type generate individuals of both types, and the respective branching law is asymptotically critical for the two-dimensional system, while being subcritical for each individual population.The main result of the paper is that the limiting behaviour of suitably scaled sums and differences of the two populations is given by a pair of measure and distribution valued processes which, together, determine the limit behaviours of the individual populations.Our proofs are based on the martingale problem approach to general state space processes. The fact that our limit involves both measure and distribution valued processes requires the development of some new methodologies of independent interest.
Markov-modulated traffic with nearly complete decomposability characteristics and associated fluid queueing models
Authors: Kontovasilis Kimon P. , Mitrou Nikolas M. 
Published: April 2006

This paper considers fluid queuing models of Markov-modulated traffic that, due to large differences in the time-scales of events, possess structural characteristics that yield a nearly completely decomposable (NCD) state-space. Extension of domain decomposition and aggregation techniques that apply to approximating the eigensystem of Markov chains permits the approximate subdivision of the full system to a number of small, independent subsystems (decomposition phase), plus an ‘aggregative' system featuring a state-space that distinguishes only one index per subsystem (aggregation phase). Perturbation analysis reveals that the error incurred by the approximation is of an order of magnitude equal to the weak coupling of the NCD Markov chain.The study in this paper is then extended to the structure of NCD fluid models describing source superposition (multiplexing). It is shown that efficient spectral factorization techniques that arise from the Kronecker sum form of the global matrices can be applied through and combined with the decomposition and aggregation procedures. All structural characteristics and system parameters are expressible in terms of the individual sources multiplexed together, rendering the construction of the global system unnecessary.Finally, besides providing efficient computational algorithms, the work in this paper can be recast as a conceptual framework for the better understanding of queueing systems under the presence of events happening in widely differing time-scales.
Expenditure patterns for risky R and D projects
Authors: Kamien Morton I. , Schwartz Nancy L. 
Published: April 2006

SummaryIn this paper we derive the time pattern of optimal planned expenditures for R and D projects in which the total effort required to complete the research satisfactorily is not known. Theorem 1 summarizes our results under alternative assumptions regarding the behavior of the function governing the supposed probability of completing the R and D satisfactorily with incremental effort. In addition, an easily employed necessary condition for the R and D project to be worthwhile is provided in Theorem 2.
The Effect of an age replacement to a standby redundant system
Authors: Mine Hisashi , Asakura Tatsuyuki 
Published: April 2006

SummaryA multiple unit standby redundant system with preventive maintenance is presented. The Laplace transform of the probability density function of the time to the first emptiness for the system and its mean time are derived. As a special case, a two-unit standby redundant system with preventive maintenance is investigated in detail.
On a stochastic process occurring in queueing systems
Authors: Bhat U. N. 
Published: April 2006

SummaryTransition distribution functions (d.f.) of the stochastic processu+t−X(t), whereX(t) has a compound Poisson distribution, are used to derive explicit results for the transition d.f.s of the waiting time processes in the queueing systemsM/G/1 andGI/M/1.
Modelling yeast cell growth using stochastic branching processes
Authors: Green P. J. 
Published: April 2006

This paper aims to demonstrate that the general Crump–Mode–Jagers branching process may be used in a natural way to model the asymmetric growth of budding yeast cells. The models obtained are generalisations of the deterministic model proposed by Hartwell and Unger (1977): all the results that are derived in that paper may be obtained using branching-process methods, but such methods also apply when account is taken of the biologically obvious fact that the various phases of the cell growth are of random rather than fixed duration. In their full generality, branching processes involve more parameters than can be estimated by experiment, but we present below a special case in which this problem is not likely to arise.A recent paper, Lord and Wheals (1980), discusses more of the biological background than is appropriate here. In the present paper, we show how certain statistical procedures for our model may be developed.
Some classes of conditional inference procedures
Authors: Williams E. J. 
Published: April 2006

Data classified into several groups usually depend on structural and accessory parameters, the structural parameter θ being a constant for all the data, while the accessory parameters ϕ i vary between groups.For the structural parameter, inferences that are free of the accessory parameters can be made when the ϕ i admit sufficient statistics or surrogates Si, by conditioning on the Si or by constructing statistics independent of the Si.When the Si are functions of the structural parameter θ, θ is said to be endomorphic. Conditional likelihood methods are not unequivocal for endomorphic parameters; instead, inference is based on statistics independent of the Si, and so free of the ϕ i, derived from conditional distribution functions.With endomorphic parameters, since the surrogates and the statistics independent of them are functions of θ, tests of independence of these sets of statistics provide a means of making inferences about θ.
Probability maximizing approach to a secretary problem by random change-point of the distribution law of the observed process
Authors: Yoshida Minoru 
Published: April 2006

Before some random moment θ, independent identically distributed random variables x1, · ··, xθ–1 with common distribution function μ (dx) appear consecutively. After the moment θ, independent random variables xθ, xθ+1, · ·· have another common distribution function f (x)μ (dx). Our information about θ can be constructed only by successively observed values of the x's.In this paper we find an optimal stopping policy by which we can maximize the probability that the quantity associated with the stopping time is the largest of all θ + m – 1 quantities for a given integer m.
Exact distributions of kin numbers in a Galton-Watson process
Authors: Joffe A. , Waugh W. A. O'n. 
Published: April 2006

The kin number problem involves the relationship between sibship sizes and offspring numbers, and also numbers of relatives of other degrees of affinity of a random member of a population, to be called Ego. The problem has been well known to demographers for some time, but results obtained only gave expected numbers. Recently a study of it, based on the Galton-Watson process, was made, with a view to obtaining joint distributions (Waugh (1981)). In the latter study it was assumed that the population was large, and thus some of the results obtained were approximations.In the present paper exact distributions are obtained, for any size of population. This can be of use in applications, where the population considered may be a small, isolated tribe or other special group. As a theoretical investigation, it replaces some heuristic arguments with limiting properties that are intrinsic to the process and it makes it possible to evaluate the previous approximations.
Bonferroni bounds revisited
Authors: Kounias Stratis , Sotirakoglou Kiki 
Published: April 2006

Lower and upper bounds of degree m for the probability of the union of n not necessarily exchangeable events are established. These bounds may be constructed to improve the Bonferroni and the Sobel–Uppuluri bounds.An application to equi-correlated multivariate normal distribution is given.
On the maximum of random fields represented by stochastic integrals over circles
Authors: Orsingher Enzo 
Published: April 2006

In this paper we obtain an upper bound for the maximum of random fields of the form , where CP denotes circles of fixed radius and dW(P′) is a plane white noise field.The results presented are obtained by means of successive steps involving Slepian's lemma for random fields, inequalities on Brownian fields and planar stochastic integrals.
Approximations for the GI/G/c queue
Authors: Van Hoorn M. H. , Seelen L. P. 
Published: April 2006

In this paper, we give good-quality approximations for multiserver queues with general service-time distributions. For the interarrival-time distribution we consider hyperexponential distributions and mixtures of Erlang distributions with the same scale parameters. We give an algorithm to compute various operating characteristics such as the delay probability and the mean queue length.The approximations are obtained by making assumptions regarding the residual service times of services in progress at service completion epochs, whereas the arrival process is modelled exactly. As the operating characteristics are far more sensitive to changes in the parameters of the arrival process, the latter is very important.The quality of the approximations is extensively tested by using the exact results of more than 2000 cases. In heavy traffic the average relative error is up to 1% and in moderate traffic about 4%.
Slepian models for X2-processes with dependent components with application to envelope upcrossings
Authors: Lindgren Georg 
Published: April 2006

A Slepian model for the local behaviour near the level upcrossings of a x2-process with dependent Gaussian components is presented. In case of independent components, this model is shown to take on a rather simple form, thereby simplifying earlier results by Aronowich and Adler.The Slepian model is applied to the envelope of a stationary Gaussian process and used to approximate the probability of ‘empty' envelope upcrossings, i.e. the probability that an envelope upcrossing is not followed by a level crossing in the original process.
Construction of first-passage-time densities for a diffusion process which is not necessarily time-homogeneous
Authors: Jáimez R. Gutiérrez , Gonzalez A. Juan , Román P. Román 
Published: April 2006

In Giorno et al. (1988) a new method for constructing first-passage-time probability density functions is outlined. This rests on the possibility of constructing the transition p.d.f. of a new time-homogeneous diffusion process in terms of a preassigned transition p.d.f. without making use of the classical space-time transformations of the Kolmogorov equation (Ricciardi (1976)).In the present paper we give an extension of this result to the case of a diffusion process X(t) which is not necessarily time-homogeneous, and a few examples are presented.
Toxicology in the Drug Discovery and Development Process
Authors: Dorato Michael A. , Buckley Lorrene A. 
Published: April 2006

AbstractThe primary objective of toxicology studies in the drug development process is to evaluate the safety of potential drug candidates. This is accomplished using relevant animal models and validated procedures. The ultimate goal is to translate the animal model responses into an understanding of the risk for human subjects. To this end, the toxicologist must be aware of the international guidelines for safety evaluation, as well as traditional and nontraditional toxicology models. As described in this unit, the typical toxicology profile consists of safety pharmacology, genetic toxicology, acute and subchronic toxicology, chronic toxicology, absorption, distribution, metabolism, and excretion (ADME) studies, reproductive and developmental toxicology, and an evaluation of carcinogenic potential.
Unidirectional development of CD8+ central memory T cells into protective Listeria‐specific effector memory T cells
Authors: Huster Katharina M. , Koffler Martina , Stemberger Christian , Schiemann Matthias , Wagner Hermann , Busch Dirk H. 
Published: April 2006

AbstractThree distinct subsets of antigen‐experienced CD8+ T cells have been identified so far: short‐living effector T cells (TEC) and two long‐living subsets, described as central (TCM) and effector memory (TEM) T cells. The lineage relationships of these subpopulations as well as their involvement in protection have not yet been conclusively determined. We recently described a novel marker combination (CD127 and CD62L) to identify all three major CD8+ T cell subsets in mice infected with Listeria monocytogenes (L.m.). Extensive lineage relationship analyses on highly purified subpopulations after in vitro and in vivo stimulation demonstrated that TCM can develop into TEM or TEC, whereas TEM can only progress to TEC cells. Short‐living TEC never regained a TEM or TCM phenotype. These data strongly suggest a hierarchical and unidirectional order of developmental stages. In vivo priming protocols that preferentially induced one of the different CD8+ T cell subsets demonstrated that predominance of TEM (CD40 stimulation) correlated best with effective protection against L.m., whereas generation of neither TCM (by immunization with heat‐killed L.m.) nor TEC (by systemic co‐administration of CpG during primary infection) conferred substantial long‐term protective immunity. These findings have important implications for the design of more effective T cell‐based vaccines.