bluuebunny/crossref_metadata_2025 huggingface dataset:
Molecular Motions in Highly Disordered Solid Phases of [(CH3)3NCH2CH3]X (X = ClO4, PF6, NO3) Studied by 1H, 19F, and 14N NMR, Powder X-Ray Diffraction, and Differential Scanning Calorimetry
Authors: Ono Hiroshi , Ishimaru Shin’ichi , Ikeda Ryuichi , Ishida Hiroyuki
Published: June 2006

1H, 19F, and 14N NMR, powder X-ray diffraction, and differential scanning calorimetry (DSC) were measured in trimethylethylammonium perchlorate, hexafluorophosphate and nitrate, [(CH3)3NCH2CH3]X (X = ClO4, PF6, NO3). Three, four and four solid phases were obtained for perchlorate, hexafluorophosphate, and nitrate, respectively, in the temperature ranges from 77 K to their decomposition temperatures. X-Ray powder patterns showed that the highest-temperature solid phases of perchlorate and hexafluorophosphate are CsCl-type cubic, while that of nitrate is NaCl-type cubic. The second highest-temperature phases of perchlorate and hexafluorophosphate form tetragonal lattices. The NMR study revealed that the cations perform isotropic rotation as well as self-diffusion in the CsCl-type cubic and tetragonal phases of perchlorate. In the cubic phase of hexafluorophosphate, isotropic rotation and self-diffusion of both anion and cation were observed. In the NaCl-type cubic phase of nitrate, isotropic rotation of both ions was detected. The structures in the highest- and second highest-temperature phases of the three salts were found to be dynamically disordered. Especially, the highest-temperature phases of perchlorate and hexafluorophosphate can be classified into the ionic plastic phase of the CsCl-type structure. Activation energies of the ionic motions in these phases were evaluated. Motional modes of the ions in the lower temperature phases were also deduced.
A New Macrocyclic Ligand-Based Sensor for Nickel(II) Ions
Authors: Singh Ashok Kumar , Bhattacharjee Gurudas , Singh Manendra , Chandra Sudeshna
Published: June 2006

A new 14-membered macrocyclic ligand containing nitrogen donor atoms was prepared and characterized. The macrocycle behaves as a selective chelating ion exchanger for some metal ions. The PVC-based membrane electrode of the macrocycle shows a Nernstian response for nickel(II) ions over a wide concentration range (0.294 to 58.69 × 102 mg dm−3) between pH 3.0 to 7.0. The electrode is found to possess adequate stability and specific selectivity with a response time of 10 s. The sensor can also be used in a partially nonaqueous medium having a 35% (v/v) nonaqueous content. The membrane exhibits excellent selectivity for nickel(II) ions, and no disturbance is observed by normal interferents like Cu2+, Cd2+, Co2+, Pb2+, Zn2+, Mg2+, and Hg2+ ions. The electrode has been successfully used for estimating Ni2+ ions in milk powders, chocolates, and hydrogenated vegetable oils. Small amounts (≤5.0 × 10−5 mol dm−3) of hexadecyltrimethylammonium bromide do not disturb the functioning of the membrane sensor.
Synthesis of Some Crystal Forms of Strontium Sulfite by Metasilicate Gel Method and Crystal Form Control
Authors: Kohiruimaki Takayuki , Matsuda Keizo
Published: June 2006

The purpose of this study is to synthesize strontium sulfite crystals with characteristic forms by a metasilicate gel-growth method and to determine the optimum conditions for synthesis of the crystals. Strontium ions were diffused into metasilicate gel including sulfite ions in order to synthesize strontium sulfite crystals. The crystals were synthesized in the pH range of 4.0 to 11.0, at a diffusion temperature between 5 and 40 °C, in the following concentration ranges: sodium sulfite, 0.2 to 1.5 mol dm−3, and strontium chloride, 0.2 to 3.0 mol dm−3. As a result, strontium sulfite crystals were obtained in the following four forms: spherical, poly-spherical, ellipsoidal, and spindle. The cause of the crystal form change was found to be a difference in the growth side by comparison of X-ray diffraction patterns. In addition, the optimum conditions which controlled the crystal form were influenced by the pH value in the gel and the temperature.
Synthesis and Complexation Behavior of Diaza-18-crown-6 Carrying Two Pyrenylmethyl Groups
Authors: Kubo Kanji , Kato Nobuo , Sakurai Tadamitsu
Published: June 2006

N,N′-Bis(1-pyrenylmethyl)-1,4,10,13-tetraoxa-7,16-diazacyclooctadecane (1) and N-(1-pyrenylmethyl)-1,4,7,10,13-pentaoxa-16-azacyclooctadecane (2) were synthesized and found to display unique photophysical properties in the presence of the guest-metal salts. The binding of metal ions to the diazacrown ether 1 cavity inhibited the exciplex formation and changed the distance between two pyrenyl groups. This caused not only an emission-intensity enhancement, but also a large change in the monomer/excimer fluorescence-intensity ratio. The change resulted from the coordinated structure and exchange process between the free host 1 and its metal salt complex in the ground state.
Substituent Effects on the Solvolysis of 2,2,2-Trifluoro-1,1-diphenylethyl Tosylates. II. 3-Chlorophenyl- and 3,5-Dichlorophenyl-Fixed Systems
Authors: Fujio Mizue , Morimoto Hiroshi , Kim Hyun-Joong , Tsuno Yuho
Published: June 2006

The solvolysis rates of 2,2,2-trifluoro-1-(3-chlorophenyl)-1-(substituted phenyl)ethyl and 2,2,2-trifluoro-1-(3,5-dichlorophenyl)-1-(substituted phenyl)ethyl tosylates or bromides were conductimetrically measured at 25.0 °C in 80% aqueous ethanol. The 3-chlorophenyl-fixed series showed a bilinear Yukawa–Tsuno correlation with ρ = −4.81 and r = 1.41 for substituents more deactivating than 3,5-dimethyl, and with ρ = −6.19 and r = 1.57 for the substituent range more activating than 4-methyl. The bilinear correlation was interpreted in terms of the changing coplanarity of the two aryl rings. The 3,5-dichlorophenyl-fixed substrates gave an excellent linear Yukawa–Tsuno correlation for the substituents ranging from 4-MeO to 4-Cl with ρ = −5.95 and r = 1.69. The variable aryl rings in this series show the largest extent of resonance interaction with the extraordinary deactivated carbenium ion center by α-CF3 and α-(3,5-dichlorophenyl) groups in the transition state. The optimization of the geometries of 2,2,2-trifluoro-1,1-diphenylethyl cation and some ring-substituted derivatives was performed at the RHF/6-31G* level. The symmetric diaryl cations have equivalently twisted conformations, while in unsymmetric ones the more stabilizing aryl group is less twisted from the plane of the positive sp2 carbon. The observed variation of r and ρ parameters is accommodated by geometrical changes of the incipient cation.
Syntheses and Crystal Structures of ET and BETS Salts Containing Bis(dithiosquarato)metalate Anions
Authors: Tanaka Hisashi , Kobayashi Akiko , Kobayashi Hayao
Published: June 2006

A series of cation radical salts of bis(ethylenedithio)tetrathiafulvalene (ET) and bis(ethylenedithio)tetraselenafulvalene (BETS) as donors and bis(dithiosquarato)metalate ([M(dts)2]n−) as anions were synthesized. The electrical resistivities of most of these salts ((BETS)2[Pd(dts)2] (1), (BETS)2[Pd(dts)2]·2(1,1,2,2-TCE) (2) (1,1,2,2-TCE = 1,1,2,2-tetrachloroethane), (BETS)[Au(dts)2] (4), (ET)2[Pd(dts)2] (5), (ET)2[Pt(dts)2] (6), and (ET)[Au(dts)2] (7)) were semiconductive. However, one of the BETS salts with [Pd(dts)2], whose donor : anion ratio was 5 : 1. (BETS)x[Pd(dts)2] (x ≈ 5.0) (3), showed a metallic behavior down to 4 K. Although the crystal structure of these semiconducting salts was a kind of mixed stacks, many short contacts within the sum of the van der Waals radii were seen between chalcogens of the donors, and between chalcogens of the donor and anion. In addition, four terminal oxygen atoms of bis(dithiosquarato)metalate anion had C–H···O hydrogen bonds with terminal ethylene groups of ET and BETS, which was one of the factors determining the conformation of the terminal ethylene groups in these crystals.
Perfluoroalkylsulfonyl-Substituted Azobenzenes as Second-Order Nonlinear Optical Chromophores
Authors: Matsui Masaki , Kawase Ritsu , Funabiki Kazumasa , Muramatsu Hiroshige , Shibata Katsuyoshi , Ishigure Yoshinao , Hirota Kazuo , Hosoda Masahiro , Tai Kazuo
Published: June 2006

4-Perfluoroalkylsulfonyl (RfSO2)-substituted azo nonlinear optical chromophores (NLOphores) showed enhanced second-order nonlinear coefficients (d33) and improved relaxation behavior compared with the corresponding nitro compound (Disperse Red 1 (DR 1)) in both doped poly(methylmethacrylate) (PMMA) and pendanted methylmethacrylate (MMA) copolymer.
Liquid-Crystalline Properties of Alkyl 4-[2-(Perfluorooctyl)ethoxy]benzoates
Authors: Okamoto Hiroaki , Murai Hiroshi , Takenaka Shunsuke
Published: June 2006

This paper describes the liquid-crystalline properties of alkyl 4-[2-(perfluorooctyl)ethoxy]benzoates (1) and bromo (2) and nitro (3) substituted compounds. For 1, the lower members show a smectic A phase; also the smectic A-isotropic transition temperatures and the latent heats decrease with increasing the carbon number of the hydrocarbon chain. An X-ray examination indicated that the smectic A phase has an interdigited arrangement of molecules. The results are discussed in terms of inter- and intra-layer fluorophilic interactions around the perfluorooctyl groups.
Frictional Ignition Testing of Composite Materials
Authors: Peralta S , Rosales K , Robinson MJ , Stoltzfus J
Published: June 2006

The space flight community has been investigating lightweight composite materials for use in propellant tanks for both liquid and gaseous oxygen for space flight vehicles. The use of these materials presents some risks pertaining to ignition and burning hazards in the presence of oxygen. Through the hazard analysis process, some ignition mechanisms have been identified as being potentially credible. One of the ignition mechanisms was reciprocal friction; however, test data do not exist that could be used to clear or fail these types of materials as “oxygen compatible” for the reciprocal friction ignition mechanism. Therefore, testing was performed at the NASA Johnson Space Center White Sands Test Facility to provide data to evaluate this ignition mechanism. This paper presents the test system, approach, data results, and findings of the reciprocal friction testing performed on composite sample materials being considered for propellant tanks.
Life-Threatening Sepsis Caused by Burkholderia cepacia From Contaminated Intravenous Flush Solutions Prepared by a Compounding Pharmacy in Another State
Authors: Held Melissa R. , Begier Elizabeth M. , Beardsley Diana S. , Browne Frederick A. , Martinello Richard A. , Baltimore Robert S. , McDonald L. Clifford , Jensen Bette , Hadler James L. , Dembry Louise-Marie
Published: June 2006

We report 2 life-threatening cases of Burkholderia cepacia sepsis caused by infusate contamination during compounding. Bacterial isolates from the patients' blood cultures and the infusate were indistinguishable by pulsed-field gel electrophoresis. Proper quality controls at a local and national level are important for ensuring safe delivery of compounded medications to patients in all settings, including those outside health care facilities.
Vertical Mandibular Alveolar Bone Distraction and Dental Implant Placement: A Case Report
Authors: Peñarrocha-Diago Miguel , Gómez-Adrián M. Dolores , García-García Abel , Camacho-Alonso Fabio , Rambla-Ferrer Javier
Published: June 2006

Extensive bone defects complicate the adequate placement of dental implants and the required angulation. In such cases, alveolar-ridge augmentation techniques such as guided bone regeneration, particulate or block grafting, and alveolar bone distraction are needed. The present study describes a case in which a large vertical bone defect in the anterior mandibular zone was corrected via vertical alveolar bone distraction. Six dental implants were posteriorly placed for implant-supported restoration of the mandible, with early implant loading. The clinical and radiologic control showed good implant and soft tissue conditions 12 months later.
Effect of Vitamin D Pretreatment of Human Mesenchymal Stem Cells on Ectopic Bone Formation
Authors: De Kok I. J. , Hicok K. C. , Padilla R. J. , Young R. G. , Cooper L. F.
Published: June 2006

Adult mesenchymal stem cells (MSCs) are used in contemporary strategies for tissue engineering. The MSC is able to form bone following implantation as undifferentiated cells adherent to hydroxyapatite (HA)/tricalcium phosphate (TCP) scaffolds. Previous investigators have demonstrated that human MSCs (hMSCs) can be differentiated to osteoblasts in vitro by the inclusion of vitamin D and ascorbic acid. The aim of this study was to compare the osteogenic potential of predifferentiated and undifferentiated bone marrow–derived, culture-expanded hMSCs adherent to synthetic HA/TCP (60%/40%) following subcutaneous engraftment in severe combined immunodeficiency (SCID) mice. During the final 3 days of culture, cells were grown in Dulbecco's modified Eagle's medium containing 10% fetal calf serum and antibiotics or media containing 25-mM calcium supplementation with vitamin D and ascorbic acid. Four weeks following implantation in SCID mice, scoring analysis of bone formation within the cubes revealed the absence of bone formation in unloaded cubes. Bone formation compared by a qualitative bone index was 7.23% for undifferentiated cells compared to 5.20% for differentiated cells. Minimal resorption was observed at this early time point. In this ectopic model, predifferentiation using a combination of vitamin D and ascorbic acid failed to increase subsequent bone formation by implanted cells. Following implantation of hMSCs adherent to an osteoconductive scaffold, host factors may contribute dominant osteoinductive signals or impose inhibitory signals to control the fate of the implanted cell. Predifferentiation strategies require confirmation in vivo.
Maxillary Sinus Augmentation Using an Engineered Porous Hydroxyapatite: A Clinical, Histological, and Transmission Electron Microscopy Study in Man
Authors: Mangano Carlo , Scarano Antonio , Iezzi Giovanna , Orsini Giovanna , Perrotti Vittoria , Mangano Francesco , Montini Sergio , Piccirilli Marcello , Piattelli Adriano
Published: June 2006

Porous hydroxyapatite (HA) is a calcium-phosphate–based material that is biocompatible, nonimmunological, and osteoconductive, and has a macroporosity of about 200 to 800 μm. The pores seem to be able to induce migration, adhesion, and proliferation of osteoblasts inside the pore network and to promote angiogenesis inside the pore system. The aim of this study was to evaluate the clinical behavior and the histological and ultrastructural aspects of porous HA in maxillary sinus augmentation procedures. Twenty-four patients (19 men, 5 women; average age 53.4 years) in good general physical and mental health and with partially or completely edentulous maxillae were selected for this study. Six months after sinus floor elevation, at the time of dental implant placement, biopsies were carried out under local anesthesia. These bone cores were cut in half and were processed for light and transmission electron microscopy. After a mean 3 years after implantation, all implants are clinically in function and no surgical or prosthetic complications have occurred. Under light microscopy, newly formed bone was 38.5% ± 4.5%, whereas the residual biomaterial represented 12% ± 2.3% and the marrow spaces represented 44.6% ± 4.2%. In addition, in the majority of cases, the biomaterial particles were in close contact with the bone, which appeared compact with the characteristic features of well-organized lamellar bone. A cement-like line was slightly visible at the bone-biomaterial interface, but there were no gaps or interposed connective tissue in between. A high quantity (about 40%) of newly formed bone was present. Bone was closely apposed to the biomaterials particles as shown in light microscopy and transmission electron microscopy. Moreover, no signs of inflammatory cell infiltrate or foreign body reaction were present. Also, most of the biomaterial was resorbed and only a small quantity (a little more than 10%) was still present. The results of our study show that porous HA can be a suitable synthetic material for bone regeneration in maxillary sinus augmentation procedures.
Use of stiffness inserts in pile groups and piled rafts
Authors: Poulos H. G.
Published: June 2006

In all but small symmetrical pile group configurations, the load distribution will be non-uniform, with a tendency for larger loads to be carried by piles near the perimeter of the pile group, while the inner piles may carry a significantly smaller load. If the design requires that a certain minimum factor of safety be applied to individual piles, the load that can be applied to a pile group may be limited by the most heavily loaded pile in that group. This may lead to an over-conservative design in many cases. This paper describes the use of stiffness inserts at the head of the more heavily loaded piles in a group. These inserts consist of a compressible material incorporated in the head of a pile, below the pile cap. By selecting appropriate stiffnesses for these inserts, it is possible to obtain an almost uniform distribution of axial load within the group, together with a specified settlement. In this way, the allowable load on a group can be increased, usually at the cost of a modest increase in the settlement. The paper sets out a relatively simple method for assessing the required stiffness of the inserts, which involves firstly an analysis of the pile group without inserts in order to compute the stiffness of each pile within the group environment. On the basis of this analysis, the required insert stiffness for each pile can be computed. The paper gives two examples of the difference in the load–settlement characteristics of a pile group with and without stiffness inserts where non-uniform load and/or settlement behaviour would occur without the inserts. A third case involves a piled raft, and demonstrates that improved settlement performance may be achieved without compromising the requirements for ultimate vertical capacity.
Modelling the bearing capacity of displacement piles in sand
Authors: Broere W. , van Tol A. F.
Published: June 2006

For complex geotechnical constructions, especially in cases with complex load combinations or strong interaction with neighbouring structures, the use of finite elements is common. One notable exception is the design of driven or soil-displacement piles and the calculation of their bearing capacity. The correct modelling of the pile installation process in finite elements proves to be difficult, whereas the influence on the stresses and the soil properties surrounding the pile is large, and subsequently the influence on the bearing capacity is large. The current study investigates the various pitfalls when attempting to use a standard finite element package for this purpose. To this end, different modelling approaches have been used, and the results have been compared with two model tests of displacement piles installed in flight in a geotechnical centrifuge. A complete modelling of the installation process is still unattainable. However, even without modelling the installation in detail, an acceptable prediction of bearing capacity can be obtained using a well-defined series of modelling steps. An advantage of the modelling approach presented in this study is that the input parameters for the soil need not be calibrated based on a pile load test, but could be obtained from a (more cost-effective) site investigation.
Performance of bored piles with different construction methods
Authors: Chen C. S. , Hiew L. C.
Published: June 2006

The design of bored piles in residual soil is usually based on empirical correlation with the results of the standard penetration test, regardless of the construction method of the bored pile. This paper presents the pile load test results of two bored piles with different construction methods. A preliminary bored pile of 1000 mm diameter was constructed using a wet method with bentonite as the stabilising fluid. The static pile load test result shows that the shaft friction could be overestimated by the empirical method. A 1200 mm diameter bored pile was constructed about 5 m away from the preliminary bored pile but using the dry method. The static pile load test result shows that higher shaft friction can be obtained. The empirical method could underestimate the shaft friction in this case.
Nonparametric standard errors and confidence intervals
Authors: Efron Bradley
Published: June 2006

We investigate several nonparametric methods; the bootstrap, the jackknife, the delta method, and other related techniques. The first and simplest goal is the assignment of nonparametric standard errors to a real‐valued statistic. More ambitiously, we consider setting nonparametric confidence intervals for a real‐valued parameter. Building on the well understood case of confidence intervals for the median, some hopeful evidence is presented that such a theory may be possible.
Interval estimates for variance components
Authors: Wild C. J.
Published: June 2006

The fiducial approach to the two components of variance random effects model developed by Venables and James (1978) is related to the Bayesian approach of Box and Tiao (1973). The operating characteristics, under repeated sampling, of the resulting interval estimators for the “within classes” variance component are investigated, and the behaviour of the two sets of intervals is found to be very similar, the coverage frequency of 95% probability intervals being approximately 91% when the “between classes” variance component is zero but rising rapidly to 95% as the between component increases. The probability intervals are shown to be shorter on average than a comparable confidence interval based upon the within classes sum of squares, and to be robust against nonnormality in the class means.
The search for submarine pingos in the Beaufort Sea: An unusual application of the binomial distribution
Authors: Johnson B. R.
Published: June 2006

Almost all statistical estimation problems involving the binomial distribution occur with the number of independent Bernoulli trials, n, being a known parameter and the probability of success, p, being unknown. Applications in which n is unknown and p is known are extremely rare. One such application to a real problem in the physical sciences is the subject of this note.
Monte Carlo studies of some adaptive robust procedures for location
Authors: Forst Frederick R. , Ali Mir Masoom
Published: June 2006

One linear and two nonlinear adaptive robust procedures have been developed in which preliminary statistics, based on tail lengths, attempt to identify distributions from which the samples arise so that a suitable robust estimator based on trimmed means can be used to estimate the location parameter. The efficiencies of the estimators based on the three proposed adaptive robust procedures have been obtained using Monte Carlo methods involving eight distributions and these efficiencies are compared with the efficiencies of nineteen other robust estimators.
Reconstruction échantillonnale d'une forme convexe
Authors: Moore Marc , Laniel Normand
Published: June 2006

Lors des études de sol effectuées en vue de l'érection du barrage LG‐3, on rencontra le problème consistant à localiser un important dépǒt de moraine enfoui à une certaine profondeur. Une approche statistique pour la solution d'un tel problème est suggérée. Elle repose sur le choix séquentiel de points échantillonnaux le long de droites traversant la région, et l'observation de la nature du sol en ces points. L'information recueillie est utilisée, dans un contexte de théorie de la décision, pour estimer certains points de la frontière de la région inconnue. A l'aide de ces estimations, une approximation de la frontière entière est construite. Une illustration de l'approche suggérée est produite à l'aide d'un programme d'ordinateur conçu à cet effet.
The multitype branching random walk, I
Authors: Gail Ivanoff B.
Published: June 2006

The limiting behaviour of the multitype branching random walk is studied. A limit theorem is proven for the supercritical process. Steady‐state distributions are shown to exist for the subcritical process with immigration, and for the critical transient process beginning with Poisson random fields. An analogue of the exponential limit law is proven for the critical process whose migration process is Brownian motion in two dimensions.
On the asymptotic null distribution of the F‐statistic for testing a partial null hypothesis in a randomized PBIB design with m associate classes under the Neyman model
Authors: Ogawa Junjiro , Ikeda Sadao
Published: June 2006

In the paper [11], the authors have shown that the familiar central F‐distribution can be considered as an asymptotically approximate distribution, in a heuristic sense, of the null distribution of the F‐statistic for testing a partial null hypothesis in a randomized PBIB design with m associate classes under the Neyman model. This result is the most general among those given in previous related papers [6, 7, 8, 9, 11]. The term “asymptotically approximate distribution” has been used, however, in a rather heuristic and unsophisticated way and the rigorous formulation of the notion of asymptotically approximate distribution has not yet been attempted. The purposes of the present article are to give a satisfactory formulation of the asymptotically approximate distribution based on Ikeda's theory of the asymptotic equivalence of probability distributions [2, 5] and to show that the familiar centrals F‐distribution is “an asymptotically approximate distribution”, in the sense just defined, of the F‐statistic for testing a partial null hypothesis in the analysis of a PBIB design with m associate classes, even under the Neyman model when it is randomized. The tedious calculations of the previous paper [11] are eliminated and the rather rigid uniformity conditions are weakened in the present article. The present work throws some light on the asymptotic nature of the power function of the F‐statistic under consideration; this will be presented in a forthcoming paper based on [4].
Evaluation of misclassification errors
Authors: Srivastava M. S.
Published: June 2006

In this paper the problem of classifying an individual into one of two multivariate normal populations with common covariance matrix is considered. An attempt is made to provide some idea about the errors of misclassification for the Welch‐Anderson statistic. It is shown that in most cases the usual asymptotic expression (the one when all the parameters are known) is an underestimate of the actual error committed. In Part II, an alternative classification procedure, known as a step‐down procedure, is proposed. In this the errors of misclassification are easily computable.
A simplified statistical estimation procedure for regional econometric models
Authors: Karasek Mirek
Published: June 2006

This paper is concerned with some computational aspects of Fisher's simultaneous‐equation estimator in its modified version [15] and with the alternative of using this computational scheme as the first stage of the two‐stage instrumental variables (2 SIV) estimator [1, p. 11]. The main disadvantage of the above estimation process arises out of the repeated investigation of a given set of instruments to determine how significantly some of their combinations contribute to R̄2. A short‐cut procedure that eliminates this computational inconvenience is suggested in this paper. The new method treats the problem within the framework of operations research, i.e., by isolating the optimum combination through the shortest way possible. The resulting step‐wise algorithm leads to the optimum combination of the given instrumental variables in, at most, n steps, where n is the number of instruments. The results of the application of this procedure to the estimation of the Ontario Econometric Model [9] are discussed, tested and compared with other methods of estimation.
A characterization of the pareto distribution
Authors: Ahsanullah M. , Kabir A. B. M. Lutful
Published: June 2006

Suppose that in a random sample of size n from a population with probability density function f(x), the order statistics are X(1) <x(2) <…<x(n). It is proved that a necessary and sufficient condition for f (x) to be a Pareto density function is that the statistics X(r) and X(s)/X(r) ≤ r < s ≤ n) are independent.
Robust M‐estimators of multivariate location and scatter in the presence of asymmetry
Authors: Wiens D. P. , Zheng Z.
Published: June 2006

Robust estimation of location vectors and scatter matrices is studied under the assumption that the unknown error distribution is spherically symmetric in a central region and completely unknown in the tail region. A precise formulation of the model is given, an analysis of the identifiable parameters in the model is presented, and consistent initial estimators of the identifiable parameters are constructed. Consistent and asymptotically normal M‐estimators are constructed (solved iteratively beginning with the initial estimates) based on “influence functions” which vanish outside specified compact sets. Finally M‐estimators which are asymptotically minimax (in the sense of Huber) are derived.
Some finite sample properties of generalized ridge regression estimators
Authors: Kadiyala Krishna
Published: June 2006

In this paper we study the mean square error properties of the generalized ridge estimator. We obtain the exact and the approximate bias and the mean square error of the operational generalized ridge estimator in terms of G( ) functions. We show, among other things, that the operational generalized ridge estimator does not dominate the ordinary least squares estimator up to a certain order of approximation. Finally, we note that the iterative procedures to obtain coverging ridge estimators should be used with caution.
γ‐Confidence tolerance regions
Authors: Evans M.
Published: June 2006

Tolerance regions are discussed that have the property of covering an event of interest with prescribed confidence γ. An exact expression is derived for the evaluation of confidence levels for tolerance regions associated with the multivariate regression model with normal error.
On the poisson approximation to the multinomial distribution
Authors: McDonald David R.
Published: June 2006

Let Xi be the number of outcomes in class Ci, i = 0,…,k, during n independent possibly non‐identical trials. If class C0 has high probability we show {Xi}ki=1 can be approximated by {Yi}ki=1 a sequence of independent Poisson random variables with ℰXi=ℰYi. A bound on the error is given. The result is an extension of Hodges and LeCam's (1960) Poisson‐binomial approximation. Applications to goodness of fit and to the sign test are given.
Case study in data analysis, no. 2
Authors: Gentleman Jane F. , Whitmore G. A.
Published: June 2006

In November 1979, the derailment of a train passing through Mississauga, Ontario, caused the explosion of tank cars containing liquid propane and the leakage of chlorine through a hole in another tank car, Officials evacuated more than 200,000 people from the area, but firemen stayed, exposing themselves to noxious fumes from the explosions and fires. When the crisis was over, health officials administered health tests and questionnaires to the affected men and to a control group of unaffected firefighters. Health information was gathered again one and two years later. In this study, two independent sets of analysts examine the health data to determine whether exposure to hazardous chemicals at the derailment site had any lasting effects on the lung function of the Mississauga firefighters.
Improved shrinkage estimators for the mean vector of a scale mixture of normals with unknown variance
Authors: Bravo Gina , Macgibbon Brenda
Published: June 2006

The problem of estimating the mean θ of a not necessarily normalp‐variate (p> 3) distribution with unknown covariance matrix of the form σ2A (Aa known diagonal matrix) on the basis ofni> 2 observations on each coordinateXt(1 <i < p) is considered. It is argued that the class of scale (or variance) mixtures of normal distributions is a reasonable class to study. Assuming the loss function is quadratic, a large class of improved shrinkage estimators is developed in the case of a balanced design. We generalize results of Berger and Strawderman for one observation in the known‐variance case. This methodology also permits the development of a new class of minimax shrinkage estimators of the mean of a p‐variate normal distribution for an unbalanced design. Numerical calculations show that the improvements in risk can be substantial.
A note on L1 consistent estimation
Authors: Yatracos Yannis G.
Published: June 2006

Let (𝒳, 𝒜) be a space with a σ‐field, M = {Ps; s o} a family of probability measures on A, Θ arbitrary, X1,…,Xn independently and identically distributed P random variables. Metrize Θ with the L1 distance between measures, and assume identifiability. Minimum‐distance estimators are constructed that relate rates of convergence with Vapnik‐Cervonenkis exponents when M is “regular”. An alternative construction of estimates is offered via Kolmogorov's chain argument.
Determination of anaerobic threshold
Authors: Bennett G. W.
Published: June 2006

This report describes the estimation of the parameters for a model of ventilation (y) by human subjects as a two‐segment linear function of oxygen uptake (x). Experimental data were supplied by R.L. Hughson of the Department of Kinesiology. The analysis of one of nine available sets of data is described in detail.
Exact confidence regions for species assignment based on DNA markers
Authors: Almudevar Anthony
Published: June 2006

Assignment of individuals to correct species or population of origin based on a comparison of allele profiles has in recent years become more accurate due to improvements in DNA marker technology. A method of assessing the error in such assignment problems is présentés. The method is based on the exact hypergeometric distributions of contingency tables conditioned on marginal totals. The result is a confidence region of fixed confidence level. This confidence level is calculable exactly in principle, and estimable very accurately by simulation, without knowledge of the true population allele frequencies. Various properties of these techniques are examined through application to several examples of actual DNA marker data and through simulation studies. Methods which may reduce computation time are discussed and illustrated.
k‐sample rank tests using pair‐specific scoring functions
Authors: Archambault W. A. T. , Mack G. A. , Wolfe D. A.
Published: June 2006

In this paper we consider generalizations of the distribution‐free one‐way ANOVA test procedures studied by Puri (1965), such generalizations allowing for possibly different scoring functions for different pairs of samples. The asymptotic distributions of the test statistics are derived and formulas for the asymptotic relative efficiencies of these tests with respect to a parametric competitor are obtained. Applications of these procedures to settings of ordered and umbrella alternatives are presented and potential advantages of this pair‐specific scoring scheme are discussed.
A note on a strong renewal theorem
Authors: Mohan N. R.
Published: June 2006

Let {Sn, n≥ 1} be a sequence of partial sums of independent and identically distributed non‐negative random variables with a common distribution functionF.LetFbelong to the domain of attraction of a stable law with exponent α, 0 < α < 1. Suppose H(t) = ϵ N(t), t ⩾ 0, whereN(t)=max(n : Sn≥ t). Under some additional assumptions onF, the difference betweenH(t)and its asymptotic value as t → ∞ is estimated.
On the distribution of quadratic forms in normal random variables
Authors: Tan W. Y.
Published: June 2006

This paper provides necessary and sufficient conditions for a quadratic form in singular normal random variables to be distributed as a given linear combination of independent noncentral chi‐square variables. Using this result, an extension of Cochran's theorem to quadratic forms of noncentral chi‐square variables is derived.
On principles and arguments to likelihood
Authors: Evans Michael J. , Fraser Donald A. S. , Monette Georges
Published: June 2006

Birnbaum (1962a) argued that the conditionality principle (C) and the sufficiency principle (S) implied the likelihood principle (L); he then argued (Birnbaum 1972) that C and a mathematical equivalence principle M implied L. Evans, Fraser, and Monette (1985a) gave reference details, and this paper gives proof that C alone implies L. The level of support by the profession for L is sharply less than that for S or even for C; thus the paradoxical nature of these results. In this regard, we elaborate on the Monette example (Fraser, Monette, and Ng 1984), which provides a strong case against L. We also examine closely the various proofs linking the principles and find that S and C can each be used operationally to suppress information otherwise deemed relevant. From another viewpoint this says that S and C can each be used in contexts that directly conflict with the original examples and motivations supporting them; the principles can thus be viewed as inappropriately used, or more strongly, as invalid. In either case, the result that C and S imply L or that C implies L can be regarded as noneffective in the context of discriminating applications. A resolution of the apparent anomalies can be obtained by allowing the statistical model to include ingredients additional to those usually present (particularly for subsequent use with conditionality), or alternatively by restricting the application of the principles to contexts where the conflicts would seem not to arise.
Weighted empirical spacings processes
Authors: CsÖRGOT Mikloas , HorvÁTH† Lajos
Published: June 2006

We give a complete asymptotic characterization of the supremum of weighted empirical spacings processes.
A law of large numbers for the scaled age distribution of linear birth‐and‐death processes
Authors: Bose A.
Published: June 2006

It is shown that certain measure‐valued stochastic processes describing the age distribution of particles whose development is controlled by linear critical birth‐and‐death processes converge in distribution to a deterministic positive bounded measure.
A family of admissible minimax estimators of the mean of a multivariate, normal distribution
Authors: Li Tze Fen , Bhoj Dinesh S.
Published: June 2006

LetXhas ap‐dimensional normal distribution with mean vector θ and identity covariance matrixI. In a compound decision problem consisting of squared‐error estimation of θ, Strawderman (1971) placed a Beta (α, 1) prior distribution on a normal class of priors to produce a family of Bayes minimax estimators. We propose an incomplete Gamma(α, β) prior distribution on the same normal class of priors to produce a larger family of Bayes minimax estimators. We present the results of a Monte Carlo study to demonstrate the reduced risk of our estimators in comparison with the Strawderman estimators when θ is away from the zero vector.
A note on the residual median process
Authors: Ghosh J. K. , Mustafi C. K.
Published: June 2006

We study the residual median process, defined as the median of those observations which are greater than a number t. Using appropriate limit theorems, it is shown that the stochastic process converges in law to a Gaussian process defined in terms of a Brownian bridge.
Mixture models in survival analysis: Are they worth the risk?
Authors: Farewell Vernon T.
Published: June 2006

There has been a recurring interest in models for survival data which hypothesize subpopulations of individuals highly susceptible to some type of adverse event. Other individuals are assumed to be at much less risk. Most commonly, in clinical trials, these models attempt to estimate the fraction of patients cured of disease. The use of such models is examined, and the likelihood function is advocated as an informative inference tool.
Bayesian incorporation of repeated measurements in logistic discrimination
Authors: Andrews D. F. , Brant R. , Percy M. E.
Published: June 2006

A common problem in medical statistics is the discrimination between two groups on the basis of diagnostic information. Information on patient characteristics is used to classify individuals into one of two groups: diseased or disease‐free. This classification is often with respect to a particular disease. This discrimination has two probabilistic components: (1) the discrimination is not without error, and (2) in many cases the a priori chance of disease can be estimated. Logistic models (Cox 1970; Anderson 1972) provide methods for incorporating both of these components. The a posteriori probability of disease may be estimated for a patient on the basis of both current measurement of patient characteristics and prior information. The parameters of the logistic model may be estimated on the basis of a calibration trial. In practice, not one but several sets of measurements of one characteristic of the patient may be made on a questionable case. These measurements typically are correlated; they are far from independent. How should these correlated measurements be used? This paper presents a method for incorporating several sets of measurements in the classification of a case.
Estimation for aggregate models: The aggregate Markov chain
Authors: Mcleish D. L.
Published: June 2006

An argument in favour of projecting the score function for models involving incomplete data is presented. Projection is then applied to the aggregate Markov‐chain model resulting in weighted least‐squares estimators. The limit theory and efficiency of these estimators are studied using martingale limit theory.
Statistical inference for some Volterra population processes in a random environment
Authors: Guttorp Peter , Kulperger Reg
Published: June 2006

We study the problem of maximum‐likelihood estimation in some random‐environment population models, defined through nonlinear ltǒ stochastic differential equations. It is shown that a criticality parameter can be estimated consistently. The asymptotic behavior of the estimators is analyzed, and a goodness‐of‐fit test is proposed.
On statistical transform methods and their efficiency
Authors: Feuerverger Andrey , Mcdunnough Philip
Published: June 2006

General conditions for the asymptotic efficiency of certain new inference procedures based on empirical transform functions are developed. A number of important processes, such as the empirical characteristic function, the empirical moment generating function, and the empirical moments, are considered as special cases.
Empirical and rank processes of observations and residuals
Authors: Shorack Galen R.
Published: June 2006

Empirical and rank processes of a sample are shown to converge under weak conditions. These results are then extended to analogous empirical and rank processes formed from the residuals of a linear model. Representations of the limiting processes are obtained by means of a special construction. The technicalities are honed to require few regularity conditions.
Strassen type limit points for moving averages of a wiener process
Authors: Chan A. H. C. , Csörgö M. , Révész P.
Published: June 2006

Let {W(s); 8 ≥ 0} be a standard Wiener process, and let βN = (2aN (log (N/aN) + log log N)‐1/2, 0 < αN ≤ N < ∞, where αN↑ and αN/N is a non‐increasing function of N, and define γN(t) = βN[W(nN + taN) − W(nN)), 0 ≥ t ≥ 1, with nN = N – aN. Let K = {x ϵ C[0,1]: x is absolutely continuous, x(0) = 0 and

}. We prove that, with probability one, the sequence of functions {γN(t), t ϵ [0,1]} is relatively compact in C[0,1] with respect to the sup norm ||·||, and its set of limit points is K. With aN = N, our result reduces to Strassen's well‐known theorem. Our method of proof follows Strassen's original, direct approach. The latter, however, contains an oversight which, in turn, renders his proof invalid. Strassen's theorem is true, of course, and his proof can also be rectified. We do this in a somewhat more general context than that of his original theorem. Applications to partial sums of independent identically distributed random variables are also considered.
A note on the admissibility of hammersley's estimator of an integer mean
Authors: Khan Rasul A.
Published: June 2006

LetX1,X2, …,Xnbe identically, independently distributedN(i,1) random variables, wherei= 0, ±1, ±2, … Hammersley (1950) showed that d = [X̄n], the nearest integer to the sample mean, is the maximum likelihood estimator ofi. Khan (1973) showed thatdis minimax and admissible with respect to zero‐one loss. This note now proves a conjecture of Stein to the effect that in the class of integer‐valued estimatorsdis minimax and admissible under squared‐error loss.
On two approximations to the F‐distribution: Application to testing for intraclass correlation in family studies
Authors: Donner Allan , Wells George A. , Eliasziw Michael
Published: June 2006

Two approximations to the F‐distribution are evaluated in the context of testing for intraclass correlation in the analysis of family data. The evaluation is based on a computation of empirical significance levels and a comparison between p‐values associated with these approximations and the corresponding exact p‐values. It is found that the approximate methods may give very unsatisfactory results, and exact methods are therefore recommended for general use.
Consistent deconvolution in density estimation
Authors: Devroye Luc
Published: June 2006

Suppose we have n observations from X = Y + Z, where Z is a noise component with known distribution, and Y has an unknown density f. When the characteristic function of Z is nonzero almost everywhere, we show that it is possible to construct a density estimate fn such that for all f, Iimn| |=0.
A functional central limit theorem for the quadratic variation of a class of gaussian random fields
Authors: Deo C. M.
Published: June 2006

We prove a central limit theorem for the quadratic variation process of some Lévy‐Baxter‐type Gaussian random fields.
Bayesian break‐point forecasting in parallel time series, with application to university admissions
Authors: Rubin D. B. , Stroud T. W. F.
Published: June 2006

A regular supply of applicants to Queen's University in Kingston, Ontario is provided by 65 high schools. Each high school can be characterized by a series of grading standards which change from year to year. To aid admissions decisions, it is desirable to forecast the current year's grading standards for all 65 high schools using grading standards estimated from past year's data. We develop and apply a Bayesian break‐point time‐series model that generates forecasts which involve smoothing across time for each school and smoothing across schools. “Break point” refers to a point in time which divides the past into the “old past” and the “recent past” where the yearly observations in the recent past are exchangeable with the observations in the year to be forecast. We show that this model works fairly well when applied to 11 years of Queen's University data. The model can be applied to other data sets with the parallel time‐series structure and short history, and can be extended in several ways to more complicated structures.
Tests for the multivariate two‐sample problem based on empirical probability measures
Authors: Kim Kang‐Kyun , Foutz Robert V.
Published: June 2006

Nonparametric tests are proposed for the equality of two unknown p‐variate distributions. Empirical probability measures are defined from samples from the two distributions and used to construct test statistics as the supremum of the absolute differences between empirical probabilities, the supremum being taken over all possible events. The test statistics are truly multivariate in not requiring the artificial ranking of multivariate observations, and they are distribution‐free in the general p‐variate case. Asymptotic null distributions are obtained. Powers of the proposed tests and a competitor are examined by Monte Carlo techniques.