bluuebunny/crossref_metadata_2025 huggingface dataset:
State aggregation and discrete-state Markov chains embedded in a class of point processes
Authors: Cao Xi-Ren
Published: April 2006

One result that is of both theoretical and practical importance regarding point processes is the method of thinning. The basic idea of this method is that under some conditions, there exists an embedded Poisson process in any point process such that all its arrival points form a sub-sequence of the Poisson process. We extend this result by showing that on the embedded Poisson process of a uni- or multi-variable marked point process in which interarrival time distributions may depend on the marks, one can define a Markov chain with a discrete state that characterizes the stage of the interarrival times. This implies that one can construct embedded Markov chains with countable state spaces for the state processes of many practical systems that can be modeled by such point processes.
Les familles exponentielles statistiques invariantes par les groupes du cône et du paraboloide de révolution
Authors: Letac Gérard
Published: April 2006

Statistical exponential families invariant with respect to the groups of the cone or the paraboloid of revolution are discussed. B(x, y) denotes the symmetric bilinear form on x0y0 – x1y1 – ·· ·– xdyd on ℝd+1, C denotes the cone of revolution in ℝd+1 {x; B(x,x) > 0 and x0 > 0}, and, for p > ½(d−1), μ p is the positive measure on ℝd+1 defined by its Laplace transform ⨍ exp (B(x,y))μp(dy) = (B(y,y))−p for y on C. More precisely, if p > ½ (d−1) one has

and μ½(d−1) concentrated on the boundary ∂C. This paper studies the natural exponential families
Last round betting
Authors: S. Ferguson Thomas , Melolidakis C.
Published: April 2006

Two players with differing amounts of money simultaneously choose an amount to bet on an even-money win-or-lose bet. The outcomes of the bets may be dependent and the player who has the larger amount of money after the outcomes are decided is the winner. This game is completely analyzed. In nearly all cases, the value exists and optimal strategies for the two players that give weight to a finite number of bets are explicitly exhibited. In a few situations, the value does not exist.
Asymptotic stationarity of queueing processes
Authors: Szczotka Władysław
Published: April 2006

We show that if an input process ζ to a queue is asymptotic stationary in some sense, satisfies a condition AB and some other natural conditions, then the output processes (w, ζ) and (w, q,ζ) are asymptotic stationary in the same sense. Here, w and q are the waiting time and queue length processes, respectively.
A sample-path approach to Palm probabilities
Authors: Stidham Shaler
Published: April 2006

Previous papers have established sample-path versions of relations between marginal time-stationary and event-stationary (Palm) state probabilities for a process with an imbedded point process. This paper extends the use of sample-path analysis to provide relations between frequencies for arbitrary (measurable) sets in function space, rather than just marginal (one-dimensional) frequencies. We define sample-path analogues of the time-stationary and event-stationary (Palm) probability measures for a process with an imbedded point process, and then derive sample-path versions of the Palm transformation and inversion formulas.
A Dam with seasonal input
Authors: Lund Robert B.
Published: April 2006

This paper examines the infinitely high dam with seasonal (periodic) Lévy input under the unit release rule. We show that a periodic limiting distribution of dam content exists whenever the mean input over a seasonal cycle is less than 1. The Laplace transform of dam content at a finite time and the Laplace transform of the periodic limiting distribution are derived in terms of the probability of an empty dam. Necessary and sufficient conditions for the periodic limiting distribution to have finite moments are given. Convergence rates to the periodic limiting distribution are obtained from the moment results. Our methods of analysis lean heavily on the coupling method and a stochastic monotonicity result.
On Cowan and Mecke's Markov chain
Authors: Liu Huaigao
Published: April 2006

In the paper, we discuss the properties of Cowan and Mecke's Markov chain P in general form. We give some criteria for determining whether the chain P is transient, recurrent null or recurrent non-null, and for the chain P to have invariant measures.
An invariant of representations of phase-type distributions and some applications
Authors: Commault C. , Chemla J. P.
Published: April 2006

In this paper we consider phase-type distributions, their Laplace transforms which are rational functions and their representations which are finite-state Markov chains with an absorbing state. We first prove that, in any representation, the minimal number of states which are visited before absorption is equal to the difference of degree between denominator and numerator in the Laplace transform of the distribution. As an application, we prove that when the Laplace transform has a denominator with n real poles and a numerator of degree less than or equal to one the distribution has order n. We show that, in general, this result can be extended neither to the case where the numerator has degree two nor to the case of non-real poles.
Asymptotic expansions for functionals of dilation of point processes
Authors: Borovkov A. A.
Published: April 2006

This paper provides a direct approach to obtaining formulas for derivatives of functionals of point processes in rare perturbation analysis ([2], [6]). Results are obtained for arbitrary (not necessarily stationary) point processes in and d, d 2, under transparent conditions, close to minimal. Formulas for higher-order derivatives allow one to construct asymptotical expansions. The results can be useful in sensitivity analysis, in light traffic theory for queues and for computation by simulation of derivatives at positive intensity, while the computation of the derivatives via statistical estimation of the functional itself and its increments usually gives poor results.
Heavy traffic analysis for continuous polling models
Authors: Kroese Dirk P.
Published: April 2006

We consider a continuous polling system in heavy traffic. Using the relationship between such systems and age-dependent branching processes, we show that the steady-state number of waiting customers in heavy traffic has approximately a gamma distribution. Moreover, given their total number, the configuration of these customers is approximately deterministic.
A stationary Poisson departure process from a minimally delayed infinite server queue with non-stationary Poisson arrivals
Authors: Barnes John A. , Meili Richard
Published: April 2006

The points of a non-stationary Poisson process with periodic intensity are independently shifted forward in time in such a way that the transformed process is stationary Poisson. The mean shift is shown to be minimal. The approach used is to consider an Mt/Gt/∞ queueing system where the arrival process is a non-stationary Poisson with periodic intensity function. A minimal service time distribution is constructed that yields a stationary Poisson departure process.
On dispersion of stable random vectors and its application in the prediction of multivariate stable processes
Authors: Soltani A. Reza , Moeanaddin R.
Published: April 2006

Our aim in this article is to derive an expression for the best linear predictor of a multivariate symmetric α stable process based on many past values. For this purpose we introduce a definition of dispersion for symmetric α stable random vectors and choose the linear predictor which minimizes the dispersion of the error vector.
Ageing first-passage times of Markov processes: a matrix approach
Authors: Li Haijun , Shaked Moshe
Published: April 2006

Using a matrix approach we discuss the first-passage time of a Markov process to exceed a given threshold or for the maximal increment of this process to pass a certain critical value. Conditions under which this first-passage time possesses various ageing properties are studied. Some results previously obtained by Li and Shaked (1995) are extended.
A note on single server loss systems with a superposition of inputs
Authors: Willie Helmut
Published: April 2006

Explicit formulas for the time congestion and the call blocking probability are derived in a single server loss system whose total input consists of a finite superposition of independent general stationary traffic streams with exponentially distributed service times. The results are used for studying to what extent two arrival processes with coinciding customer-stationary state distributions are similar or even identical, and whether an arrival process with coinciding customer-stationary and time-stationary state distributions is of the Poisson type.
Compound Poisson approximations for word patterns under Markovian hypotheses
Authors: Geske Mark X. , Godbole Anant P. , Schaffner Andrew A. , Skolnick Allison M. , Wallstrom Garrick L.
Published: April 2006

Consider a stationary Markov chainwith state space consisting of theξ-letter alphabet set Λ= {a1, a2, ···,aξ}.We study the variablesM=M(n, k) andN=N(n, k),defined, respectively, as the number of overlapping and non-overlapping occurrences of a fixed periodick-letter word, and use the Stein–Chen method to obtain compound Poisson approximations for their distribution.
On the MX/G/∞ queue by heterogeneous customers in a batch
Authors: Cong Tang Dac
Published: April 2006

We consider the Mx/G/∞ queue in which customers in a batch belong to k different types, and a customer of type i requires a non-negative service time with general distribution function Bi(s) (1 ≦ i ≦ k). The number of customers in a batch is stochastic. The joint probability generating function of the number of customers of type i being served at a fixed time t > 0 is derived by the method of collective marks.
On the saturation rule for the stability of queues
Authors: Baccelli François , Foss Serguei
Published: April 2006

This paper focuses on the stability of open queueing systems under stationary ergodic assumptions. It defines a set of conditions, the monotone separable framework, ensuring that the stability region is given by the following saturation rule: ‘saturate' the queues which are fed by the external arrival stream; look at the ‘intensity' μ of the departure stream in this saturated system; then stability holds whenever the intensity of the arrival process, say λ satisfies the condition λ < μ, whereas the network is unstable if λ > μ. Whenever the stability condition is satisfied, it is also shown that certain state variables associated with the network admit a finite stationary regime which is constructed pathwise using a Loynes-type backward argument. This framework involves two main pathwise properties, external monotonicity and separability, which are satisfied by several classical queueing networks. The main tool for the proof of this rule is subadditive ergodic theory. It is shown that, for various problems, the proposed method provides an alternative to the methods based on Harris recurrence and regeneration; this is particularly true in the Markov case, where we show that the distributional assumptions commonly made on service or arrival times so as to ensure Harris recurrence can in fact be relaxed.
The escape probability for integrated Brownian motion with non-zero drift
Authors: Atkinson R. A. , Clifford Peter
Published: April 2006

We consider the two-dimensional process {X(t), V(t)} where {V(t)} is Brownian motion with drift, and {X(t)} is its integral. In this note we derive the joint density function of T and V(T) where T is the time at which the process {X(t)} first returns to its initial value. A series expansion of the marginal density of T is given in the zero-drift case. When V(0) and the drift are both positive there is a positive probability that {Χ (t)} never returns to its initial value. We show how this probability grows for small drift. Finally, using the Kontorovich–Lebedev transform pair we obtain the escape probability explicitly for arbitrary values of the drift parameter.
A probabilistic interpretation of the degree of fuzziness
Authors: Handa Kenji , Kalukottege Prasansa , Ogura Yukio
Published: April 2006

In this paper we give a probabilistic interpretation for the function d(f), which has been proposed as a measure of fuzziness of a fuzzy set f. For this we construct random patterns which approximate the fuzzy set f and show that, for large n, the number of possible outcomes of the nth random pattern is approximately 2nd(f). We also give the best possible constant K in a more accurate approximation .
Heavy traffic analysis of a transportation network model
Authors: Peterson William P. , Wein Lawrence M.
Published: April 2006

We study a model of a stochastic transportation system introduced by Crane. By adapting constructions of multidimensional reflected Brownian motion (RBM) that have since been developed for feedforward queueing networks, we generalize Crane's original functional central limit theorem results to a full vector setting, giving an explicit development for the case in which all terminals in the model experience heavy traffic conditions. We investigate product form conditions for the stationary distribution of our resulting RBM limit, and contrast our results for transportation networks with those for traditional queueing network models.
Dimensioning a multiple hashing scheme
Authors: Barbour A. D. , Phatarfod R. M.
Published: April 2006

The number of items of data which are irretrievable without additional effort after hashing can be greatly reduced if several hash tables are used simultaneously. Here we show that, in a multiple hashing scheme, this number has a distribution very close to Poisson. Thus choosing the number and sizes of the tables to minimize theexpectednumber of irretrievable items is the right way to dimension a scheme.
Modelling and predicting urban atmospheric pollutants in the Aosta Valley region of Italy using a site‐optimised model
Authors: Dirks Kim N. , Nanni Alessandro , Dirks Vincent I.
Published: April 2006

An effective simple site‐optimised urban air pollution model for predicting CO, PM10, NO and NO2 concentrations is developed for the topographically complex region of the Aosta Valley in Italy. The good results suggest that such a model could be used to ‘downscale’ mesoscale‐forecasted surface conditions to give real‐time site‐specific pollution predictions. Copyright © 2006 Royal Meteorological Society
An improved regularization for time‐staggered discretization and its link to the semi‐implicit method
Authors: Wood Nigel , Staniforth Andrew , Reich Sebastian
Published: April 2006

A regularized time‐staggered discretization of the shallow‐water equations has recently been proposed. Here, a new form of the regularization operator is presented. This form addresses a weakness in the original formulation so that now the discretization preserves the analytic forced response. Because the reformulation takes account of the forcing terms in the equations, if the unregularized equations are in balance, in the sense that ∇.(Du/Dt) vanishes, then the regularized equations maintain this balance. Copyright © 2006 Royal Meteorological Society
Design and Synthesis of Simple Macrocycles Active Against Vancomycin‐Resistant Enterococci (VRE)
Authors: Jia Yanxing , Ma Nianchun , Liu Zuosheng , Bois‐Choussy Michèle , Gonzalez‐Zamora Eduardo , Malabarba Adriano , Brunati Cristina , Zhu Jieping
Published: April 2006

16‐membered meta,para‐cyclophanes mimicking the vancomycin binding pocket (D–O–E ring) were designed and synthesized. The structural key features of these biaryl ether containing macrocycles are (1) the presence of β‐amino‐α‐hydroxy acid or α,β‐diamino acid as the C‐terminal component of the cyclopeptide and (2) the presence of a hydrophobic chain or lipidated aminoglucose at the appropriate position. Cycloetherification by an intramolecular nucleophilic aromatic substitution reaction (SNAr) is used as the key step for the construction of the macrocycle. The atropselectivity of this ring‐closure reaction is found to be sensitive to the peptide backbone and chemoselective cyclization (phenol versus primary amine) is achievable. Glycosylation of phenol was realized with freshly prepared 3,4,6‐tri‐O‐acetyl‐2‐N‐lauroyl‐2‐amino‐2‐deoxy‐α‐D‐glucopyranosyl bromide under phase‐transfer conditions. Minimum inhibitory concentrations for all of the derivatives are measured by using a standard microdilution assay, and potent bioactivities against both sensitive and resistant strains are found for some of these compounds (MIC (minimum inhibitory concentration)=4 μg mL−1 against VRE). From these preliminary SAR studies, it was anticipated that both the presence of a hydrophobic substituent and an appropriate structure of the macrocycle were required for this series of compounds to be active against VRE.
Fast Fourier Continuous Cyclic Voltammetry at Gold Ultramicroelectrode in Flowing Solution for Determination of Ultra Trace Amounts of Penicillin G
Authors: Norouzi Parviz , Ganjali Mohammad Reza , Alizadeh Taher , Daneshgar Parandis
Published: April 2006

In this work, for the first time a fast continuous cyclic voltammetry was used as a highly sensitive detection method for Penicillin G in a flow‐injection system. A special computer‐based numerical calculation method (using Fast Fourier Transformation) is introduced here for enhancing the analyte signal and noise reduction. During the measurements, the potential waveform (consists of potential steps for cleaning, stripping and potential ramp) was continuously applied on an Au disk microelectrode (with a radius 12.5 μm in radius). The stripping time was less than 200 ms. Effects of rest potential, sweep rate, and delay time on the sensitivity of the method were investigated. The limit of detection of the method was 1.0 × 10−11 M. The detection limit of the method is 660 times lower than the most sensitive reported method. The relative standard deviation of the method at 1.0×10−7 M of Penicillin G was 2.7% for 10 runs.
Silver(I)‐Selective PVC Membrane Potentiometric Sensor Based on a Recently Synthesized Calix[4]arene
Authors: Demirel Ayça , Doğan Alev , Akkuş Gülderen , Yılmaz Mustafa , Kılıç Esma
Published: April 2006

A new PVC membrane potentiometric sensor for Ag(I) ion based on a recently synthesized calix[4]arene compound of 5,11,17,23‐tetra‐tert‐butyl‐25,27‐dihydroxy‐calix[4]arene‐thiacrown‐4 is developed. The electrode exhibits a Nernstian response for Ag(I) ions over a wide concentration range (1.0×10−2−1.0×10−6 M) with a slope of 53.8±1.6 mV per decade. It has a relatively fast response time (5–10 s) and can be used for at least 2 months without any considerable divergence in potentials. The proposed electrode shows high selectivity towards Ag+ ions over Pb2+, Cd2+, Co2+, Zn2+, Cu2+, Ni2+, Sr2+, Mg2+, Ca2+, Li+, K+, Na+, NH4+ ions and can be used in a pH range of 2–6. Only interference of Hg2+ is found. It is successfully used as an indicator electrode in potentiometric titration of a mixture of chloride, bromide and iodide ions.
An instrumented scaffold can monitor loading in the knee joint
Authors: Szivek J. A. , Bliss C. L. , Geffre C. P. , Margolis D. S. , DeYoung D. W. , Ruth J. T. , Schnepp A. B. , Tellis B. C. , Vaidyanathan R. K.
Published: April 2006

No technique has been consistently successful in the repair of large focal defects in cartilage, particularly in older patients. Tissue‐engineered cartilage grown on synthetic scaffolds with appropriate mechanical properties will provide an implant, which could be used to treat this problem. A means of monitoring loads and pressures acting on cartilage, at the defect site, will provide information needed to understand integration and survival of engineered tissues. It will also provide a means of evaluating rehabilitation protocols. A “sensate” scaffold with calibrated strain sensors attached to its surface, combined with a subminiature radio transmitter, was developed and utilized to measure loads and pressures during gait. In an animal study utilizing six dogs, peak loads of 120N and peak pressures of 11 MPa were measured during relaxed gait. Ingrowth into the scaffold characterized after 6 months in vivo indicated that it was well anchored and bone formation was continuing. Cartilage tissue formation was noted at the edges of the defect at the joint–scaffold interfaces. This suggested that native cartilage integration in future formulations of this scaffold configured with engineered cartilage will be a possibility. © 2006 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 2006
Cover Picture: Macromol. Rapid Commun. 9/2006
Authors: Jhon Young K. , Bhat Rajendra R. , Jeong Changwoo , Rojas Orlando J. , Szleifer Igal , Genzer Jan
Published: April 2006

Cover: Quartz crystal microbalance with dissipation monitoring is used to probe the effect of salt concentration on the phase transition behavior of thermoresponsive surface‐grafted poly(N‐isopropylacryl‐amide) (PNIPAM) brushes brushes. The phase transition temperature of grafted polymer is found to decrease as the concentration of salt is increased. This depression in phase transition temperature is similar to that observed for free polymer and is attributed to unbinding of the water molecules from the PNIPAM by the presence of ions. Further details can be found in the article by Y. K. Jhon, R. R. Bhat, C. Jeong, O. J. Rojas, I. Szleifer, and J. Genzer* on page 697.
Three‐stage contingent screening for Down syndrome
Authors: Wright Dave , Bradbury Ian , Cuckle Howard , Gardosi Jason , Tonks Ann , Standing Sue , Benn Peter
Published: April 2006

Objective

To demonstrate the potential value of three‐stage sequential screening for Down syndrome.

Methods

Protocols were considered in which maternal serum pregnancy associated plasma protein‐A (PAPP‐A) and free β‐human chorionic gonadotropin (hCG) measurements were taken on all women in the first trimester. Those women with very low Down syndrome risks were screened negative at that stage and nuchal translucency (NT) was measured on the remainder and the risk reassessed. Those with very low risk were then screened negative and those with very high risk were offered early diagnostic testing. Those with intermediate risks received second‐trimester maternal serum α‐fetoprotein, free β‐hCG, unconjugated estriol and inhibin‐A. Risk was then reassessed and those with high risk were offered diagnosis. Detection rates and false‐positive rates were estimated by multivariate Gaussian modelling using Monte‐Carlo simulation.

Results

The modelling suggests that, with full adherence to a three‐stage policy, overall detection rates of nearly 90% and false‐positive rates below 2.0% can be achieved. Approximately two‐thirds of pregnancies are screened on the basis of first‐trimester biochemistry alone, five out of six women complete their screening in the first trimester, and the first‐trimester detection rate is over 60%.

Conclusion

Three‐stage contingent sequential screening is potentially highly effective for Down syndrome screening. The acceptability of this protocol and its performance in practice, should be tested in prospective studies. Copyright © 2006 John Wiley & Sons, Ltd.
Theoretical and experimental studies of anisotropic shrinkage in injection moldings of semicrystalline polymers
Authors: Kwon Keehae , Isayev A.I. , Kim K.H. , van Sweden C.
Published: April 2006

A novel approach to predict anisotropic shrinkage of semicrystalline polymers in injection moldings was proposed using flow‐induced crystallization, frozen‐in molecular orientation, elastic recovery, and PVT equation of state. The anisotropic thermal expansion and compressibility affected by the frozen‐in orientation function and the elastic recovery that was not frozen during moldings were introduced to obtain the in‐plane anisotropic shrinkages. The frozen‐in orientation function was calculated from amorphous and crystalline contributions. The amorphous contribution was based on the frozen‐in and intrinsic amorphous birefringence, whereas the crystalline contribution was based on the crystalline orientation function, which was determined from the elastic recovery and intrinsic crystalline birefringence. To model the elastic recovery and frozen‐in stresses related to birefringence during molding process, a nonlinear viscoelastic constitutive equation was used with temperature‐ and crystallinity‐dependent viscosity and relaxation time. Occurrence of the flow‐induced crystallization was introduced through the elevation of melting temperature affected by entropy production during flow of the viscoelastic melt. Kinetics of the crystallization was modeled using Nakamura and Hoffman‐Lauritzen equations with the rate constant affected by the elevated melting temperature. Numerous injection molding runs on polypropylene of various molecular weights were carried out by varying the packing time, flow rate, melt temperature, and mold temperature. The anisotropic shrinkage of the moldings was measured. Comparison of the experimental and simulated results indicated a good predictive capability of the proposed approach. POLYM. ENG. SCI., 46:712–728, 2006. © 2006 Society of Plastics Engineers
Vesicular catalysis of the decarboxylation of 6‐nitrobenzisoxazole‐3‐carboxylate. The effects of sugars, long‐tailed sugars, cholesterol and alcohol additives
Authors: Jongejan Mahthild G. M. , Klijn Jaap E. , Engberts Jan. B. F. N.
Published: April 2006

The effects of the addition of sugars, long‐tailed n‐alkyl pyranosides, n‐alkyl glycerol ethers and n‐alcohols on the properties of di‐n‐hexadecyldimethylammonium bromide (DHAB) vesicles have been studied. Properties that were examined include the stability, morphology, phase of the tails, and catalytic rate acceleration of the unimolecular decarboxylation of the 6‐nitrobenzisoxazole‐3‐carboxylate anion (6‐NBIC). The kinetic data were analyzed on the basis of the pseudophase model and show a rate acceleration of a factor of about 1000 relative to the reaction in water. Upon addition of most additives an inhibiting effect on the decarboxylation reaction of 6‐NBIC is observed relative to the reaction in vesicles without any additive. The largest inhibition was observed in the case of cholesterol. Contrastingly, n‐dodecyl‐β‐maltoside (in the spherical vesicle region) and trehalose accelerate the reaction. The activation parameters show that the most significant contribution to the Gibbs energy of activation is the enthalpic factor, with a partly compensating entropic contribution. Copyright © 2006 John Wiley & Sons, Ltd.
Syntheses and properties of hyperbranched polybenzoxazole by thermal cyclodehydration of hyperbranched poly[o‐(t‐butoxycarbonyl)amide] via A2 + B3 approach
Authors: Kudo Hiroto , Maruyama Ken , Shindo Syoko , Nishikubo Tadatomi , Nishimura Isao
Published: April 2006

The syntheses and properties of hyperbranched poly(o‐hydroxyamide) [poly(HAB‐BCC)‐ABP], poly[o‐(t‐butoxycarbonyl)amide] [poly(HAB‐BCC)‐ABP‐t‐BOC], and polybenzoxazole [poly(HAB‐cycloBCC)] were examined. Poly(HAB‐BCC)‐ABP was obtained from the polycondensation reaction of 3,3‐dihydroxy‐4,4′‐diaminobiphenyl (HAB) as an A2‐monomer and 1,3,5‐benzenetricarboxylchloride (BCC) as a B3‐monomer with 2‐amino‐4‐t‐butylphenol (ABP) in NMP in the presence of pyridine for 24 h. The reaction of poly(HAB‐BCC)‐ABP and di‐t‐buthylcarbonate (DiBOC) was performed to obtain the corresponding poly(HAB‐BCC)‐ABP‐t‐BOC with pendant t‐BOC groups. The thermal cyclodehydration of poly(HAB‐BCC)‐ABP‐t‐BOC was carried out in the film sate at 400 °C, affording the poly(HAB‐cyclo‐BCC) in quantitative yield. Furthermore, the solubilities and thermal properties of these polymers were examined. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 3640–3649, 2006
Resampling and deconvolution of linear time‐of‐flight records for enhanced protein profiling
Authors: Malyarenko Dariya I. , Cooke William E. , Tracy Eugene R. , Drake Richard R. , Shin Susanna , Semmes O. John , Sasinowski Maciek , Manos Dennis M.
Published: April 2006

We have developed a peak deconvolution strategy that is applicable to the full mass range of a time‐of‐flight (TOF) spectrum. This strategy involves resampling a spectrum to create a time series that has equal peak widths (in time) across the entire spectrum, and then using the deconvolution filters we have previously described. We use this technique to deconvolve the protein mass spectra for blood serum and cell lysates acquired on three separate TOF instruments. Following deconvolution, we resolve spectral structures consistent with expected events such as multiply charged ions, matrix adducts and post‐translational protein modifications. The deconvolution procedure produces a 40% improvement in the resolution and enhanced experimental sensitivity over the full length of the linear TOF record, up to m/z 150 000. This approach is particularly appropriate for automated data analysis and peak detection in dense TOF spectra. Copyright © 2006 John Wiley & Sons, Ltd.
Examination of the food processes on mixed inferior host plants in a polyphagous grasshopper
Authors: Miura Kazumi , Ohsaki Naota
Published: April 2006

The mass gain of polyphagous grasshoppers fed a mixture of intrinsically inferior plants is often greater than that of grasshoppers fed each inferior plant alone. We examined the cause of this greater mass gain by assessing the food processes of a polyphagous grasshopper in detail. Food processes were divided into five stages: consumption, fecal mass, assimilated food, approximate digestibility, and efficiency of conversion of digested food (ECD). Using final‐stadium female nymphs of the polyphagous grasshopper Parapodisma subastris, we compared the mass gain of nymphs fed the inferior plants Polygonum cuspidatum and Weigela hortensis or the superior plant Artemisia princeps. The mass gain of nymphs fed a single inferior plant was less than that of nymphs fed the superior plant because of reduced ECD. However, the mass gain of nymphs fed a mixture of the two inferior plants was not only greater than that of nymphs fed a single inferior plant, but also did not differ from that of nymphs fed the superior plant. Since consumption by nymphs fed the mixture was greater than that by nymphs fed P. cuspidatum and smaller than that by nymphs fed W. hortensis, and since the ECD of nymphs fed the mixture was greater than that of nymphs fed W. hortensis and was not different from that of nymphs fed P. cuspidatum, consumption and ECD appeared to cause the greater mass gain in nymphs fed the mixture.
Equilibrium adsorption at crystal-melt interfaces in Lennard-Jones alloys
Authors: Becker C. A. , Asta M. , Hoyt J. J. , Foiles S. M.
Published: April 2006

Although the properties of crystal-melt interfaces have been extensively studied in pure materials, effects of alloying on the interfacial free energy remain relatively poorly understood. In this work we make use of Monte Carlo computer simulations for model binary Lennard-Jones alloys to explore the effects which variations in atomic-size mismatch and the chemical contributions to mixing energies have upon density and composition profiles, as well as the resulting magnitudes of equilibrium adsorption coefficients in concentrated alloys. We study four different model systems covering a range of chemical and size mismatch, finding relatively small adsorption values which are nevertheless statistically different from zero.
Orbital-order-induced magnetic anisotropy and intrinsic phase separation of the Pr0.50+xSr0.50−xMnO3 single crystals
Authors: Cao Shixun , Kang Baojuan , Zhang Jincang , Yuan Shujuan
Published: April 2006

Magnetization and torque magnetization measurements, together with the results of electron paramagnetic resonance experiment, were conducted on the Pr0.50+xSr0.50−xMnO3 single crystals. Orbital-order-induced strong magnetic anisotropy is found in the ferromagnetic (FM) state. It is observed by torque magnetization that magnetic anisotropy exists even in the paramagnetic (PM) and antiferromagnetic (AFM) states, indicating existence of the FM cluster in the A-type AFM state below the FM-AFM transition temperature and the PM state far above the Curie temperature. The results prove that the interplay of spin and orbital results in intrinsic phase separation in the manganite systems.
Serum levels of angiogenic factors indicate a pro‐angiogenic state in adults with sickle cell disease
Authors: Duits Ashley J. , Rodriguez Tati , Schnog John‐John B. ,   the CURAMA Study Group
Published: April 2006

Hypoxia‐induced angiogenesis may play an important role in the pathophysiology of sickle cell disease (SCD). Serum levels of angiopoietin (Ang)‐1, Ang‐2, vascular endothelial growth factor, placenta growth factor (PlGF), soluble tunica intima endothelial kinase 2 (sTIE2), erythropoietin (EPO) and endothelial activation markers (soluble vascular adhesion molecule‐1, soluble intercellular adhesion molecule‐1) were determined in controls, HbSS (n = 35) and HbSC (n = 23) patients. In the asymptomatic phase, serum Ang‐2 (P < 0·001), EPO (P < 0·001) and sTIE2 (P = 0·03) were elevated in patients. During painful crises, increased Ang‐2 (P < 0·001) and PlGF (P = 0·04) occurred in HbSS and Ang‐2 (P = 0·05) in HbSC patients. These results indicate a pro‐angiogenic state in SCD, mainly because of elevated Ang‐2 levels.
Comparison of two stainless steel files to shape simulated root canals
Authors: AL‐OMARI M.A.O. , BRYANT S. , DUMMER P.M.H.
Published: April 2006

The aim of this study was to compare the shaping ability of two stainless steel files using simulated canals. A total of 80 simulated canals of various angles and positions of curvature were prepared by hand using either Mani K‐Files or Micro Mega K‐Files. Following orifice enlargement each file type was used to prepare 40 canals employing a linear filing motion and an anticurvature stepback technique. Pre‐ and post‐operative longitudinal images of the canals were taken with a video camera and stored and manipulated in a computer with image analysis software. The presence of canal aberrations and the amount of material removed as a result of preparation were determined from composite images of superimposed pre‐ and post‐operative views. Overall, canal preparation with Mani K‐Files was significantly quicker (P7<0.0O5) and was associated with fewer instrument failures. Zips and elbows were observed in 70% of specimens with significantly more (P<0.05) occurring following preparation with Micro Mega K‐Files. Mani K‐Files created significantly more (P<0.01) danger zones. Micro Mega K‐Files created significantly wider (P<0.001) zips with significantly more (P<0.01) resin removed from the outer aspect of the curves and, thus, significantly more (P<0.01) transportation. Canal shape had a significant influence on preparation time (P<0.001), the incidence of zips (P<0.05) and danger zones (P<0.005), the width of zips (P<0.001) and transportation at the zips (P<0.001). Under the conditions of this study, Mani K‐Files were more effective than Micro Mega K‐Files and produced canals with better shapes. Original canal shape had a substantial influence on the outcome of shaping procedures.
LONG RUN DEMAND FOR LABOUR IN THE CONSUMER GOOD INDUSTRY
Authors: Steedman Ian
Published: April 2006

We consider, for alternative models of production, the comparative statics of constant‐returns economies in long run competitive equilibrium, for which reswitching, capital‐reversing and consumption‐reversal are all completely absent. Notwithstanding the ‘well‐behaved’ nature of these economies, the use of labour per unit of output in the consumer good industry is always positively related to the real wage rate.
Challenges to Introducing and Managing Disturbance Regimes for Holocarpha macradenia, an Endangered Annual Grassland Forb
Authors: HOLL KAREN D. , HAYES GREY F.
Published: April 2006

Abstract:  Introducing rare plants to new sites for conservation to offset effects of habitat destruction requires detailed knowledge of habitat requirements, plant demography, and management needs. We conducted a factorial experiment replicated at three coastal prairie sites to test the effects of clipping frequency and litter accumulation on seed germination, seedling survival, reproduction, and seedling recruitment of introduced populations of the endangered, tall‐stature, annual forb, Holocarpha macradenia (DC.) E. Greene. Clipping favored H. macradenia, primarily by enhancing seed germination and flower production. Litter accumulation had no effect on seed germination, even after 5 years of treatments. Seedling recruitment was highly site specific with large numbers of recruits recorded at only one of three sites. Although recruitment of seedlings was higher in clipped plots for 2–3 years, by 4–5 years after introduction very few seedlings survived to reproduction in any treatment. We attribute this result to a combination of poor habitat quality, small population size, and lack of a seed bank. We were unsuccessful in introducing this relatively well‐studied species of concern to apparently suitable habitat at multiple sites in multiple years, which suggests that translocating rare plant populations to mitigate for habitat destruction is an expensive and highly uncertain endeavor.
Rodent Communities in an Exurbanizing Southwestern Landscape (U.S.A.)
Authors: BOCK CARL E. , JONES ZACH F. , BOCK JANE H.
Published: April 2006

Abstract:  Ranches are being converted to exurban housing developments in the southwestern United States, with potentially significant but little‐studied impacts on biological diversity. We captured rodents on 48 traplines in grasslands, mesquite savannas, and oak savannas in southeastern Arizona that were grazed by livestock, embedded in exurban housing developments, grazed and embedded in development, or neither grazed nor embedded in development. Independent of habitat or development, rodent species richness, mean rank abundance, and capture rates of all rodents combined were negatively related to presence of livestock grazing or to its effects on vegetative ground cover. Exurban development had no obvious effects on rodent variety or abundance. Results suggest southwestern exurban developments can sustain a rich assemblage of grassland and savanna rodents if housing densities are low and houses are embedded in a matrix of natural vegetation with little grazing.
Low-Level Mesocyclonic Concentration by Nonaxisymmetric Transport. Part II: Vorticity Dynamics
Authors: Gaudet Brian J. , Cotton William R. , Montgomery Michael T.
Published: April 2006

An idealized supercell simulation using the Regional Atmospheric Modeling System (RAMS) produced an elongated low-level mesocyclone that subsequently collapsed into a concentrated vortex. Though vorticity continually increased in the mesocyclone due to horizontal convergence, the collapse phase was additionally characterized by rapidly decreasing pressure, closed streamlines, and the creation of a compact vorticity center isolated from the remaining vorticity. It was shown in Part I of this study that the concentration phase was not initiated by an increase in horizontal convergence, suggesting that the proximate cause resided elsewhere.

In this study, the vortex concentration in Part I is examined from a vorticity dynamics perspective. It is shown that concentration occurs when inward radial velocity and vertical vorticity become more spatially correlated in the region surrounding the nascent vortex. It is also emphasized that the anisotropy of the horizontal convergence, which is nearly plane-convergent and of comparable magnitude to the mesocyclonic vorticity, is critical to an understanding of the process. The resultant evolution is intermediate between a state of purely two-dimensional nondivergent dynamics and one in which plane convergence confines vorticity to its axis of dilatation. This intermediate state produces a concentrated vortex more rapidly than either end state. The unsteady nature of the initial vorticity band also serves to increase the circulation and wind speed amplification of the final vortex. It is shown how conceptual models in the fluid dynamics literature can be applied to predicting the time and length scales of tornadic mesocyclone evolution.
Arctic Ocean Ice Thickness: Modes of Variability and the Best Locations from Which to Monitor Them*
Authors: Lindsay R. W. , Zhang J.
Published: April 2006

Model simulations of Arctic sea ice and ocean systems are used to determine the major spatial and temporal modes of variability in the ice thickness. A coupled ice–ocean model is forced with daily NCEP–NCAR reanalysis surface air pressure and surface air temperature fields for the period 1951–2003 with the analysis of the results performed for the 51-yr period 1953–2003. Ice concentration data and ice velocity data (beginning in 1979) are assimilated to further constrain the simulations to match the observed conditions. The simulated ice thins over the study period with the area of greatest thinning in a band from the Laptev Sea across the Pole to Fram Strait. The thinning rate is greatest since 1988. The major spatial modes of variability were determined with empirical orthogonal functions (EOFs) for the ice thickness within the Arctic Ocean. The first three EOFs account for 30%, 18%, and 15%, respectively, of the annual mean ice thickness variance. The first EOF is a nearly basinwide pattern, and the next two are orthogonal lateral modes. Because of the nonstationary nature of the ice thickness time series, significant changes in the modes are found if a shorter period is analyzed. The second and third principal components are well correlated with the Arctic Oscillation. The model results are also used to simulate an observation system and to then determine optimal mooring locations to monitor the basinwide mean ice thickness as well as the spatial and temporal patterns represented in the EOF analysis. The nonstationary aspect of the ice thickness limits the strength of the conclusions that can be drawn.
Initially Forced Long Planetary Waves in the Presence of Nonzonal Mean Flow
Authors: Cerovečki Ivana , de Szoeke Roland A.
Published: April 2006

The purpose of this paper is to understand how long planetary waves evolve when propagating in a subtropical gyre. The steady flow of a wind-driven vertically sheared model subtropical gyre is perturbed by Ekman pumping that is localized within a region of finite lateral extent and oscillates periodically at about the annual frequency after sudden initiation. Both the background flow and the infinitesimal perturbations are solutions of a 2½-layer model. The region of forcing is located in the eastern part of the gyre where the steady flow is confined to the uppermost layer (shadow zone). The lateral scales of the forcing and of the response are supposed to be small enough with respect to the overall gyre scale that the background flow may be idealized as horizontally uniform, yet large enough (greater than the baroclinic Rossby radii) that the long-wave approximation may be made. The latter approximation limits the length of time over which the solutions remain valid. The solutions consist of (i) a forced response oscillating at the forcing frequency in which both stable (real) and zonally growing (complex) meridional wavenumbers are excited plus (ii) a localized transient structure that grows as it propagates away from the region of forcing. Application of the method of stationary phase provides analytical solutions that permit clear separation of the directly forced part of the solution and the transient as well as estimation of the temporal growth rate of the transient, which proves to be convectively unstable. The solutions presented here are relevant to understanding the instability of periodic (including annual period) perturbations of oceanic subtropical gyres on scales larger than the baroclinic Rossby radii of deformation.
Spatial Variations of Stirring in the Surface Ocean: A Case Study of the Tasman Sea
Authors: Waugh Darryn W. , Abraham Edward R. , Bowen Melissa M.
Published: April 2006

Stirring in the Tasman Sea is examined using surface geostrophic currents derived from satellite altimeter measurements. Calculations of the distribution of finite-time Lyapunov exponents (FTLEs) indicate that the stirring in this region is not uniform and stretching rates over 15 days vary from less than 0.02 day−1 to over 0.3 day−1. These variations occur at both small (∼10 km) and large (∼1000 km) scales and in both cases are linked to dynamical features of the flow. The small-scale variations are related to the characteristics of coherent vortex structures, and there are low FTLEs inside vortices and filaments of high FTLEs in strain-dominated regions surrounding these vortices. Regional variations in the stirring are closely related to variations in mesoscale activity and eddy kinetic energy (EKE). High values of mean FTLE occur in regions of high EKE (highest mean values of around 0.2 day−1 occur in the East Australia Current separation region) whereas small values occur in regions with low EKE (mean values around 0.03 day−1 in the east Tasman Sea). There is a compact relationship between the mean FTLEs and EKE, raising the possibility of using the easily calculated EKE to estimate the stirring. This possibility is even more intriguing because the FTLE distributions can be approximated, for the time scales considered here, by Weibull distributions with shape parameter equal to 1.6, which can be defined from the mean value alone.
Mechanics of neutrophil phagocytosis: experiments and quantitative models
Authors: Herant Marc , Heinrich Volkmar , Dembo Micah
Published: April 2006

To quantitatively characterize the mechanical processes that drive phagocytosis, we observed the FcγR-driven engulfment of antibody-coated beads of diameters 3 μm to 11 μm by initially spherical neutrophils. In particular, the time course of cell morphology, of bead motion and of cortical tension were determined. Here, we introduce a number of mechanistic models for phagocytosis and test their validity by comparing the experimental data with finite element computations for multiple bead sizes. We find that the optimal models involve two key mechanical interactions: a repulsion or pressure between cytoskeleton and free membrane that drives protrusion, and an attraction between cytoskeleton and membrane newly adherent to the bead that flattens the cell into a thin lamella. Other models such as cytoskeletal expansion or swelling appear to be ruled out as main drivers of phagocytosis because of the characteristics of bead motion during engulfment. We finally show that the protrusive force necessary for the engulfment of large beads points towards storage of strain energy in the cytoskeleton over a large distance from the leading edge (∼0.5 μm), and that the flattening force can plausibly be generated by the known concentrations of unconventional myosins at the leading edge.