bluuebunny/crossref_metadata_2025_split huggingface dataset:
Stereotactic Treatment of Intracerebral Hematoma by Means of a Plasminogen Activator
Authors: Teernstra O.P.M. , Evers S.M.A.A. , Lodder J. , Leffers P. , Franke C.L. , Blaauw G. 
Published: April 2003

Background and Purpose—Treatment of intracerebral hematoma (ICH) is controversial. An advantage of neurosurgical intervention over conservative treatment of ICH has not been established. Recent reports suggest a favorable effect of stereotactic blood clot removal after liquefaction by means of a plasminogen activator. The SICHPA trial was aimed at investigating the efficacy of this treatment.Methods—A stereotactically placed catheter was used to instill urokinase to liquefy and drain the ICH in 6-hour intervals over 48 hours. From 1996 to 1999, 13 centers entered 71 patients into the study. Patients were randomized into a surgical group (n=36) and a nonsurgical group (n=35). Admission criteria were the following: age >45 years, spontaneous supratentorial ICH, Glasgow Eye Motor score ranging from 2 to 10, ICH volume >10 cm3, and treatment within 72 hours. The primary end point was death at 6 months. As secondary end points, ICH volume reduction and overall outcome measured by the modified Rankin scale were chosen. The trial was prematurely stopped as a result of slow patient accrual.Results—Seventy patients were analyzed. Overall mortality at day 180 after stroke was 57%; this included 20 of 36 patients (56%) in the surgical group and 20 of 34 patients (59%) in the nonsurgical group. A significant ICH volume reduction was achieved by the intervention (10% to 20%,P<0.05). Logistic regression analysis indicated the possibility of efficacy for surgical treatment (odds ratio, 0.23; 95% confidence interval, 0.05 to 1.20;P=0.08). The odds ratio of mortality combined with modified Rankin scale score 5 at 180 days was also not statistically significant (odds ratio, 0.52; 95% confidence interval, 1.2 to 2.3;P=0.38).Conclusions—Stereotactic aspiration can be performed safely and in a relatively uniform manner; it leads to a modest reduction of 18 mL of hematoma reduction over 7 days when compared with control, which has a 7-mL reduction, and therefore may improve prognosis.
Smallest-fit selection of random sizes under a sum constraint: weak convergence and moment comparisons
Authors: Boshuizen Frans A. , Kertz Robert P. 
Published: April 2003

In this paper, in work strongly related with that of Coffman et al. [5], Bruss and Robertson [2], and Rhee and Talagrand [15], we focus our interest on an asymptotic distributional comparison between numbers of ‘smallest’ i.i.d. random variables selected by either on-line or off-line policies. Let X1,X2,… be a sequence of i.i.d. random variables with distribution function F(x), and let X1,n,…,Xn,n be the sequence of order statistics of X1,…,Xn. For a sequence (cn)n≥1 of positive constants, the smallest fit off-line counting random variable is defined by Ne(cn) := max {j ≤ n : X1,n + … + Xj,n ≤ cn}. The asymptotic joint distributional comparison is given between the off-line count Ne(cn) and on-line counts Nnτ for ‘good’ sequential (on-line) policies τ satisfying the sum constraint ∑j≥1XτjI(τj≤n) ≤ cn. Specifically, for such policies τ, under appropriate conditions on the distribution function F(x) and the constants (cn)n≥1, we find sequences of positive constants (Bn)n≥1, (Δn)n≥1 and (Δ'n)n≥1 such that
for some non-degenerate random variables W and W'. The major tools used in the paper are convergence of point processes to Poisson random measure and continuous mapping theorems, strong approximation results of the normalized empirical process by Brownian bridges, and some renewal theory.
Asymptotic results for multiplexing subexponential on-off processes
Authors: Jelenković Predrag R. , Lazar Aurel A. 
Published: April 2003

Consider an aggregate arrival process AN obtained by multiplexing N on-off processes with exponential off periods of rate λ and subexponential on periods τon. As N goes to infinity, with λN → Λ, AN approaches an M/G/∞ type process. Both for finite and infinite N, we obtain the asymptotic characterization of the arrival process activity period.Using these results we investigate a fluid queue with the limiting M/G/∞ arrival process At∞ and capacity c. When on periods are regularly varying (with non-integer exponent), we derive a precise asymptotic behavior of the queue length random variable QtP observed at the beginning of the arrival process activity periods
where ρ = 𝔼At∞ < c; r (c ≤ r) is the rate at which the fluid is arriving during an on period. The asymptotic (time average) queue distribution lower bound is obtained under more general assumptions regarding on periods than regular variation.In addition, we analyse a queueing system in which one on-off process, whose on period belongs to a subclass of subexponential distributions, is multiplexed with independent exponential processes with aggregate expected rate 𝔼et. This system is shown to be asymptotically equivalent to the same queueing system with the exponential arrival processes being replaced by their total mean value 𝔼et.
Isotropic correlation functions ond-dimensional balls
Authors: Gneiting Tilmann 
Published: April 2003

A popular procedure in spatial data analysis is to fit a line segment of the formc(x) = 1 - α ||x||, ||x|| < 1, to observed correlations at (appropriately scaled) spatial lagxind-dimensional space. We show that such an approach is permissible if and only ifthe upper bound depending on the spatial dimensiond. The proof relies on Matheron's turning bands operator and an extension theorem for positive definite functions due to Rudin. Side results and examples include a general discussion of isotropic correlation functions defined ond-dimensional balls.
Asymptotics for geometric location problems over random samples
Authors: McGivney K. , Yukich J. E. 
Published: April 2003

Consider the basic location problem in which k locations from among n given points X1,…,Xn are to be chosen so as to minimize the sum M(k; X1,…,Xn) of the distances of each point to the nearest location. It is assumed that no location can serve more than a fixed finite number D of points. When the Xi, i ≥ 1, are i.i.d. random variables with values in [0,1]d and when k = ⌈n/(D+1)⌉ we show that
where α := α(D,d) is a positive constant, f is the density of the absolutely continuous part of the law of X1, and c.c. denotes complete convergence.
On the fractal dimensions of point patterns
Authors: Vere-Jones David 
Published: April 2003

When fractal dimensions are estimated from an observed point pattern, there is some ambiguity as to the interpretation of the quantity being estimated. (The point pattern itself has dimension zero.) Two possible interpretations are described. In the first of these, the observation region is regarded as being held fixed, while observations accumulate with time. In this case, provided the process is stationary and ergodic in time, and the cumulants satisfy certain regularity constraints, the dimension estimates consistently estimate the Rényi moment dimensions of the marginal distribution in space. If the regularity constraints are not satisfied, then different limits can be obtained according to the manner in which the limits are taken.In the second case, the process is regarded as being stationary and ergodic in its spatial component, time being held fixed. In this case the estimates provide consistent estimates of the initial power-law rates of growth of the moment measures of the Palm distribution, the estimates for successively higher Rényi dimensions estimating the growth rates for successively higher-order moment measures of the Palm distribution.Several examples are given, to illustrate the different types of behaviour which may occur, including the case where the points are generated by a dynamical system.
A unified approach to fast teller queues and ATM
Authors: Beck B. , Dabrowski A. R. , McDonald D. R. 
Published: April 2003

This paper examines a problem of importance to the telecommunications industry. In the design of modern ATM switches, it is necessary to use simulation to estimate the probability that a queue within the switch exceeds a given large value. Since these are extremely small probabilities, importance sampling methods must be used. Here we obtain a change of measure for a broad class of models with direct applicability to ATM switches.We consider a model withAindependent sources of cells where each source is modeled by a Markov renewal point process with batch arrivals. We do not assume the sources are necessarily identically distributed, nor that batch sizes are independent of the state of the Markov process. These arrivals join a queue served by multiple independent servers, each with service times also modeled as a Markov renewal process. We only discuss a time-slotted system. The queue is viewed as the additive component of a Markov additive chain subject to the constraint that the additive component remains non-negative. We apply the theory in McDonald (1999) to obtain the asymptotics of the tail of the distribution of the queue size in steady state plus the asymptotics of the mean time between large deviations of the queue size.
Stochastic analysis of image acquisition, interpolation and scale-space smoothing
Authors: Åström Kalle , Heyden Anders 
Published: April 2003

In the high-level operations of computer vision it is taken for granted that image features have been reliably detected. This paper addresses the problem of feature extraction by scale-space methods. There has been a strong development in scale-space theory and its applications to low-level vision in the last couple of years. Scale-space theory for continuous signals is on a firm theoretical basis. However, discrete scale-space theory is known to be quite tricky, particularly for low levels of scale-space smoothing. The paper is based on two key ideas: to investigate the stochastic properties of scale-space representations and to investigate the interplay between discrete and continuous images. These investigations are then used to predict the stochastic properties of sub-pixel feature detectors.The modeling of image acquisition, image interpolation and scale-space smoothing is discussed, with particular emphasis on the influence of random errors and the interplay between the discrete and continuous representations. In doing so, new results are given on the stochastic properties of discrete and continuous random fields. A new discrete scale-space theory is also developed. In practice this approach differs little from the traditional approach at coarser scales, but the new formulation is better suited for the stochastic analysis of sub-pixel feature detectors.The interpolated images can then be analysed independently of the position and spacing of the underlying discretisation grid. This leads to simpler analysis of sub-pixel feature detectors. The analysis is illustrated for edge detection and correlation. The stochastic model is validated both by simulations and by the analysis of real images.
Generalized Gamma measures and shot-noise Cox processes
Authors: Brix Anders 
Published: April 2003

A parametric family of completely random measures, which includes gamma random measures, positive stable random measures as well as inverse Gaussian measures, is defined. In order to develop models for clustered point patterns with dependencies between points, the family is used in a shot-noise construction as intensity measures for Cox processes. The resulting Cox processes are of Poisson cluster process type and include Poisson processes and ordinary Neyman-Scott processes.We show characteristics of the completely random measures, illustrated by simulations, and derive moment and mixing properties for the shot-noise random measures. Finally statistical inference for shot-noise Cox processes is considered and some results on nearest-neighbour Markov properties are given.
Incomplete markets: convergence of options values under the minimal martingale measure
Authors: Prigent Jean-Luc 
Published: April 2003

In the setting of incomplete markets, this paper presents a general result of convergence for derivative assets prices. It is proved that the minimal martingale measure first introduced by Föllmer and Schweizer is a convenient tool for the stability under convergence. This extends previous well-known results when the markets are complete both in discrete time and continuous time. Taking into account the structure of stock prices, a mild assumption is made. It implies the joint convergence of the sequences of stock prices and of the Radon-Nikodym derivative of the minimal measure. The convergence of the derivatives prices follows.This property is illustrated in the main classes of financial market models.
On the Hausdorff distance between a convex set and an interior random convex hull
Authors: Bräker H. , Hsing T. , Bingham N. H. 
Published: April 2003

The problem of estimating an unknown compact convex set K in the plane, from a sample (X1,···,Xn) of points independently and uniformly distributed over K, is considered. Let Kn be the convex hull of the sample, Δ be the Hausdorff distance, and Δn := Δ (K, Kn). Under mild conditions, limit laws for Δn are obtained. We find sequences (an), (bn) such that(Δn - bn)/an → Λ (n → ∞), where Λ is the Gumbel (double-exponential) law from extreme-value theory. As expected, the directions of maximum curvature play a decisive role. Our results apply, for instance, to discs and to the interiors of ellipses, although for eccentricity e < 1 the first case cannot be obtained from the second by continuity. The polygonal case is also considered.
On the current enhancement at the edge of a crack in a lattice of resistors
Authors: Taylor Howard M. , Sweitzer Dennis E. 
Published: April 2003

Consider a network whose nodes are the integer lattice points and whose arcs are fuses of 1Ω resistance. Remove a horizontal segment ofNadjacent vertical arcs, forming a ‘crack’ of lengthN. Subject the network to a uniform potential gradient ofvvolts per arc in the north-south (or vertical) direction and measure the current in one of the two vertical arcs at the ends of the crack. We write this current in the forme(N)v, and calle(N) thecurrent enhancement.We show that the enhancement grows at a rate that is the order of the square root of the crack length. Our method is to identify the enhancement with the mean time to exit an interval for a certain integer valued random walk, and then to use some of the well-known Fourier methods for studying random walk. Our random walk has no mean or higher moments and is in the domain of attraction of the Cauchy law. We provide a good approximation to the enhancement using the explicitly known mean time to exit an interval for a Cauchy process. Weak convergence arguments together with an estimate of a recurrence probability enable us to show that the current in an intact fuse, that is in the interior of a crack of lengthN, grows p roportionally withN/logN.
Rate of convergence for computing expectations of stopping functionals of an α-mixing process
Authors: Alaya Mohamed Ben , Pagès Gilles 
Published: April 2003

Theshiftmethod consists in computing the expectation of an integrable functionalFdefined on the probability space ((ℝd)N,B(ℝd)⊗N, μ⊗N) (μ is a probability measure on ℝd) using Birkhoff's Pointwise Ergodic Theorem, i.e.asn→ ∞, where θ denotes the canonical shift operator. WhenFlies inL2(FT, μ⊗N) for some integrable enough stopping timeT, several weak (CLT) or strong (Gàl-Koksma Theorem or LIL) converging rates hold. The method successfully competes with Monte Carlo. The aim of this paper is to extend these results to more general probability distributionsPon ((ℝd)N,B(ℝd)⊗N), namely when the canonical process (Xn)n∊NisP-stationary, α-mixing and fulfils Ibragimov's assumptionfor some δ > 0. One application is the computation of the expectation of functionals of an α-mixing Markov Chain, under its stationary distributionPν. It may both provide a better accuracy and save the random number generator compared to the usual Monte Carlo or shift methods on independent innovations.
A convergence theorem for markov chains arising in population genetics and the coalescent with selfing
Authors: Möhle M. 
Published: April 2003

A simple convergence theorem for sequences of Markov chains is presented in order to derive new ‘convergence-to-the-coalescent’ results for diploid neutral population models.For the so-called diploid Wright-Fisher model with selfing probabilitysand mutation rate θ, it is shown that the ancestral structure ofnsampled genes can be treated in the framework of ann-coalescent with mutation rate ̃θ := θ(1-s/2), if the population sizeNis large and if the time is measured in units of (2-s)Ngenerations.
Failure models indexed by two scales
Authors: Singpurwalla Nozer D. , Wilson Simon P. 
Published: April 2003

Much of the literature in reliability and survival analysis considers failure models indexed by a single scale. There are situations which require that failure be described by several scales. An example from reliability is items under warranty whose failure is recorded by time and amount of use. An example from survival analysis is the death of a mine worker which is noted by age and the duration of exposure to dust.This paper proposes an approach for developing probabilistic models indexed by two scales: time, and usage, a quantity that is related to time. The relationship between the scales is described by an additive hazards model. The evolution of usage is described by stochastic processes like the Poisson, the gamma and the Markov additive. The paper concludes with an application involving the setting of warranties. Two features differentiate this work from related efforts: a use of specific processes for describing usage, and a use of Monte Carlo techniques for generating the models.
New Type of Monodispersed Gold Nanoparticles Capped by Myristate and PPh3 Ligands Prepared by Controlled Thermolysis of [Au(C13H27COO)(PPh3)]
Authors: Yamamoto Mari , Nakamoto Masami 
Published: April 2003

Abstract
Controlled thermolysis of gold(I) complex, [Au(C13H27COO)(PPh3)], at 180 °C for 5 h under an N2 atmosphere affords the new type of monodispersed spherical gold nanoparticles capped by myristate and a small amount of PPh3 ligands (average diameter 23 ± 1.5 nm), in spite of no use of solvent, reducing agent and stabilizer.
Comparing Methods of Establishing the aPTT Therapeutic Range of Heparin
Authors: Liepman Claire I , Koerber John M , Mattson Joan C , Westley Susan J , Smythe Maureen A 
Published: April 2003

BACKGROUND: The American College of Chest Physicians (ACCP) recommends that the activated partial thromboplastin time (aPTT) therapeutic range for unfractionated heparin be defined as the aPTT corresponding to a heparin concentration of 0.3–0.7 μ/mL by heparin anti-factor Xa assay. This recommendation suggests that a therapeutic range defined in this manner should be superior to traditional empiric therapeutic ranges of 1.5–2.5 times the control. A pilot study was conducted to evaluate the ACCP recommendation for heparin monitoring. OBJECTIVE: To compare heparin dosage adjustments guided by a heparin concentration–derived therapeutic range (HCDTR) with those influenced by traditional empiric therapeutic ranges for the aPTT. METHODS: This study was conducted in 2 phases. In phase 1, the various aPTT therapeutic ranges were established and/or defined. The first empiric therapeutic range (E1) was established by performing an aPTT test on healthy volunteers. This E1 was defined as 1.5–2.5 times the mean normal aPTT. A second empiric therapeutic range (E2) was defined as 1.5–2.5 times the patient's baseline aPTT. The aPTT HCDTR had been defined in a previous study as 48–61 seconds. In phase 2, heparin dosage adjustment decisions guided by each empiric range and the HCDTR for the aPTT were compared with heparin dosage adjustment decisions guided by actual heparin concentrations. Decisions were in agreement when both the aPTT result and plasma heparin concentration indicated the same dosage change. Forty patients had a bedside aPTT determined prior to receiving continuous infusion heparin and again within 48 hours of heparin initiation. Plasma heparin concentration by anti-factor Xa assay was performed on the blood samples obtained after heparin initiation. Heparin dosage adjustment decisions were evaluated by determining the agreement of each aPTT test result with the corresponding plasma heparin concentration. An overall level of agreement (defined as the % of decisions that were in agreement) for each aPTT therapeutic range was determined. RESULTS: The level of agreement in dosage adjustment decisions between heparin concentration and E1, E2, and HCDTR was 28/40 (70%), 28/39 (72%), and 23/40 (58%), respectively (p = 0.34). Heparin dosage adjustment decisions based on an aPTT HCDTR did not significantly differ from heparin dosage adjustment decisions guided by traditional empiric therapeutic ranges for a bedside aPTT. CONCLUSIONS: This pilot study showed similar heparin dosage adjustment decisions using an empiric aPTT therapeutic range versus a heparin concentration–derived aPTT therapeutic range.
Absorption of Enteral Recombinant Human Erythropoietin by Neonates
Authors: Juul Sandra E , Christensen Robert D 
Published: April 2003

BACKGROUND: Erythropoietin (EPO) is present in amniotic fluid, colostrum, and human milk. One possible function of ingested EPO might be to stimulate erythropoiesis. However, it is unclear whether human neonates absorb recombinant human erythropoietin (rhEPO) after oral administration. OBJECTIVE: To determine whether circulating EPO concentrations increase following enteral administration of rhEPO to neonates. METHODS: The study was designed as a 2-center prospective, blinded, randomized, 2 times 2 crossover study, with each infant receiving 1 dose of rhEPO 1000 units/kg and 1 dose of placebo. Serum EPO concentrations were measured at baseline, 2, and 4 hours following study drug administration. The rhEPO and placebo dosing were separated by a mean of 72 hours. Analysis was stratified by gestational age (≤35 wk, >35 wk) and feeding type (human milk, infant formula). RESULTS: No significant change in serum EPO concentration was identified at 2 or 4 hours following enteral administration of rhEPO. CONCLUSIONS: Enteral administration of a large dose of rhEPO to neonates <4 months of age did not result in increased circulating EPO concentrations at 2 or 4 hours following dosing, regardless of whether it was administered in human milk or infant formula.