bluuebunny/crossref_metadata_2025 huggingface dataset:
Ursolic acid and other pentacyclic triterpenoids stimulate intestinal alkaline sphingomyelinase in vitro
Authors: Andersson David , Nilsson Åke , Duan Rui‐Dong
Published: February 2006

Purpose: Alkaline sphingomyelinase (alk‐SMase) is an enzyme that hydrolyses sphingomyelin in a bile salt‐dependent manner in the gastrointestinal tract, and has been proposed as an inhibitor of colon carcinogenesis. Ursolic acid (UA) is a plant‐derived pentacyclic triterpenoid that has been shown to have anti‐proliferative and apoptotic effects on HT29 human colon adenocarcinoma cells, with activation of alk‐SMase as an early event. The aim of this study was to study the in vitro effects of UA and its analogues on the activity of purified rat intestinal alk‐SMase. Methods: Rat intestinal alk‐SMase activity was determined after incubation with UA in the presence and absence of taurocholate (TC). The effect was compared with boswellic acids, another group of pentacyclic triterpenoids. Results: UA enhanced the activity of rat intestinal alk‐SMase in a dose‐dependent manner, without a similar effect on bacterial neutral SMase. Four types of boswellic acid also increased the enzyme activity, with the effect of acetyl‐keto‐β‐boswellic acid being most potent. Activation of alk‐SMase by TC at a low concentration (0.4 mM), but not at a high concentration, was enhanced by UA. Conclusions: Ursolic acid and four types of boswellic acid, all pentacyclic triterpenoids, have a stimulatory effect on the activity of intestinal alk‐SMase.
Cover Picture: Chromophore‐Supported Purification in Parallel Synthesis (Eur. J. Org. Chem. 5/2006)
Authors: Aumüller Ingo , Lindhorst Thisbe K.
Published: February 2006

The cover picture shows an example of parallel column chromatography, which is part of a methodology that is called “chromophore‐supported purification” (CSP). This approach speeds up the separation of products and by‐products in parallel synthesis. CSP is based on the introduction of a suitable azulene dervative into the starting materials used in a synthetic sequence or parallel reaction. The azulene moiety serves as a chromophore and as a protecting group. This approach has facilitated the structural diversification of carbohydrate ligands, for example, as presented in the Short Communication by I. Aumüller and T. Lindhorst on p. 1103 ff.
Human endothelial cells inhibit BMSC differentiation into mature osteoblasts in vitro by interfering with osterix expression
Authors: Meury Thomas , Verrier Sophie , Alini Mauro
Published: February 2006

It is well accepted, that there is communication between osteoblasts and endothelial cells. However, the influence of endothelial cells on the differentiation of bone precursors into mature osteoblasts is not yet well understood. We therefore studied the effect of human umbilical vein endothelial cells (HUVEC) on human bone marrow stromal cell (BMSC) differentiation towards an osteoblastic phenotype by culturing them in two different types of HUVEC‐BMSC cultures (indirect contact, HUVEC‐conditioned medium). Typical bone markers (45Ca incorporation, ALP activity, and gene expression of collagen 1 (COL1), osteonectin (ON), matrix metalloproteinase 13 (MMP‐13), bone morphogenetic protein 2 (BMP‐2)) and transcription factors (Runx2, osterix (OSX)) were evaluated at different time points. The effect of stimulating HUVEC with vascular endothelial growth factor (VEGF) before co‐cultures with BMSC was also evaluated. As expected, BMSC in osteogenic medium (OM) (with dexamethasone) differentiated towards the osteoblastic phenotype, as measured by increased matrix mineralization, high ALP activity, and elevated expression of specific osteoblastic marker genes, when compared to BMSC in non‐OM. HUVEC reversibly inhibited osteoblastic differentiation of BMSC in OM, independent of the co‐culture type. When HUVEC were removed from the cultures, BMSC differentiated into osteoblasts, albeit at a faster rate than BMSC that were never co‐cultured with HUVEC. Stimulation of HUVEC with VEGF before co‐culture enhanced the inhibitory effect of HUVEC on BMSC differentiation. This inhibitory effect was connected to a reversible suppression of OSX gene expression and was specific to endothelial cells. We conclude that HUVEC can inhibit dexamethasone‐induced BMSC differentiation into osteoblasts in vitro, by interfering with OSX expression, thereby arresting BMSC differentiation at a preosteoblastic stage. J. Cell. Biochem. 98: 992–1006, 2006. © 2006 Wiley‐Liss, Inc.
A comparative theoretical study of dipeptide solvation in water
Authors: Hugosson Håkan W. , Laio Alessandro , Maurer Patrick , Rothlisberger Ursula
Published: February 2006

Molecular dynamics studies have been performed on the zwitterionic form of the dipeptide glycine–alanine in water, with focus on the solvation and electrostatic properties using a range of theoretical methods, from purely classical force fields, through mixed quantum mechanical/molecular mechanical simulations, to fully quantum mechanical Car–Parrinello calculations. The results of these studies show that the solvation pattern is similar for all methods used for most atoms in the dipeptide, but can differ substantially for some groups; namely the carboxy and aminoterminii, and the backbone amid NH group. This might have implications in other theoretical studies of peptides and proteins with charged —NH and —CO side chains solvated in water. Hybrid quantum mechanical/molecular mechanical simulations successfully reproduce the solvation patterns from the fully quantum mechanical simulations (PACS numbers: 87.14.Ee, 87.15.Aa, 87.15.He, 71.15.Pd). © 2006 Wiley Periodicals, Inc. J Comput Chem 27:672–684, 2006
Comparison of promoter region constructs forin vivointramuscular expression
Authors: Fabre Emmanuelle E. , Bigey Pascal , Orsini Cécile , Scherman Daniel
Published: February 2006

Background

High transgene expression is generally expected after gene transfer. However, different level, kinetics and localization of expression might be needed for relevant therapeutic applications. Former studies have compared various promoter regions driving gene expression leading to conflicting results. In the present work, two promoter families have been compared using the efficientin vivointramuscular electrotransfer technique.

Methods

Three promoter regions were constructed by associating the strong ubiquitous cytomegalovirus (CMV) enhancer‐promoter to its homologous intron A or to a heterologous intron, or to a hybrid intron. Promoter regions derived from the muscle creatine kinase (MCK) promoter were also studied. The expression of the same transgene (SeAP or neurotrophin‐3) under control of these different promoters was compared after plasmid electrotransfer in mouse tibialis‐cranialis skeletal muscle.

Results

Heterologous intron association to the CMV promoter did not modify gene expression kinetics nor increase gene expression level. Usefulness of intron A or hybrid intron association to the CMV promoter depended on the gene. The various MCK promoters drove efficient gene expression but lower than that obtained with the CMV promoter. Furthermore, peak value was reached earlier with MCK promoter regions (14 days).

Conclusion

For applications of gene transfer restricted to skeletal muscle, the MCK promoter or a MCK promoter variant would be a promising alternative to the CMV promoter. Indeed, it has been demonstrated that the use of MCK promoter limits humoral and cell‐mediated immune responses. Furthermore, the MCK promoter decreases the initial expression peak that may be detrimental, drives a sustained gene expression, and improves gene transfer safety. Copyright © 2006 John Wiley & Sons, Ltd.
Phase transition of L‐Ser monohydrate crystal studied by 13C solid‐state NMR
Authors: Kameda Tsunenori , Teramoto Hidetoshi
Published: February 2006

We used gravimetric analysis (GA) and 13C solid‐state nuclear magnetic resonance (NMR) to study solid‐phase transition from the transparent single crystal of L‐serine (L‐Ser) monohydrate to a turbid powder. We found that L‐Ser monohydrate loses water molecules and transforms into an anhydrate, thus experimentally demonstrating Frey's assumption (Acta Cryst., B29, 876, 1973). Application of a handmade cross‐polarization (CP) NMR probe with a saddle‐type coil to the oriented crystal of the L‐Ser monohydrate revealed the dehydration mechanism. Furthermore, the chemical shift tensor components of the carboxyl carbon in L‐Ser monohydrate were determined. The difference in the tensor component of δ22 between the monohydrate and anhydrate forms was more than 7 ppm, probably owing to differences in the hydrogen‐bonding structure of each form. Copyright © 2006 John Wiley & Sons, Ltd.
Molecular reorientation of CD4in gas‐phase mixtures
Authors: ter Horst Marc A. , Jameson Cynthia J. , Jameson A. Keith
Published: February 2006

Spin‐lattice relaxation times were measured for the deuterons in CD4in pure gas and in mixtures with the following buffer gases: Ar, Kr, Xe, HCl, N2, CO, CO2, CF4, and SF6. Effective collision cross sections σθ, 2for the molecular reorientation of CD4in collisions with these ten molecules are obtained as a function of temperature. These cross sections are compared with the corresponding cross sections σJobtained from1H spin‐rotation relaxation in mixtures of CH4with the same set of buffer gases. Various classical reorientation models typically applied in liquids predict different ratios of the reduced correlation times for the reorientation of spherical tops. The Langevin model comes closest to predicting the magnitude of the σθ, 2/σJratio that we obtain for CD4. Copyright © 2006 John Wiley & Sons, Ltd.
Carbon‐13 chemical shift anisotropy in DNA bases from field dependence of solution NMR relaxation rates
Authors: Ying Jinfa , Grishaev Alexander , Bax Ad
Published: February 2006

Knowledge of 13C chemical shift anisotropy (CSA) in nucleotide bases is important for the interpretation of solution‐state NMR relaxation data in terms of local dynamic properties of DNA and RNA. Accurate knowledge of the CSA becomes particularly important at high magnetic fields, prerequisite for adequate spectral resolution in larger oligonucleotides. Measurement of 13C relaxation rates of protonated carbons in the bases of the so‐called Dickerson dodecamer, d(CGCGAATTCGCG)2, at 500 and 800 MHz 1H frequency, together with the previously characterized structure and diffusion tensor yields CSA values for C5 in C, C6 in C and T, C8 in A and G, and C2 in A that are closest to values previously reported on the basis of solid‐state FIREMAT NMR measurements, and mostly larger than values obtained by in vacuo DFT calculations. Owing to the noncollinearity of dipolar and CSA interactions, interpretation of the NMR relaxation rates is particularly sensitive to anisotropy of rotational diffusion, and use of isotropic diffusion models can result in considerable errors. Copyright © 2006 John Wiley & Sons, Ltd.
Comparison of the performance of round and rectangular wire in small solenoids for high‐field NMR
Authors: Li Yu , Webb Andrew G. , Saha Saikat , Brey William W. , Zachariah Cherian , Edison Arthur S.
Published: February 2006

This paper considers the effects of conductor geometry on the performance of small solenoidal coils for high‐field NMR. First, a simple analytical model is presented for investigating the effects of conductor geometry on the current distribution in such coils. The model was used to derive optimum parameters for coils constructed from wire with either rectangular or circular cross‐sections as a function of the length‐to‐diameter ratio. Second, a commercial software package utilizing full three‐dimensional finite‐element solutions to Maxwell's equations was used to confirm the basic findings of the simple analytical model, and also to compare simulated S/N estimations with experimental NMR spectra acquired with 2.5 mm and 1.0 mm‐diameter solenoid coils: reasonable agreement was found. Third, as a demonstration of the usefulness of such coils for mass‐limited samples, multidimensional experiments were performed at 750 MHz on ∼4.7 nmol (41 µg) of PF1061, a protein from Pyrococcus furiosus. Copyright © 2006 John Wiley & Sons, Ltd.
Solid‐state NMR and computational studies of 4‐methyl‐2‐nitroacetanilide
Authors: Harris Robin K. , Ghi Phuong Y. , Hammond Robert B. , Ma Cai Yun , Roberts Kevin J. , Yates Jonathan R. , Pickard Chris J.
Published: February 2006

Studies on the solid‐state structure of two polymorphs of 4‐methyl‐2‐nitroacetanilide (MNA) were conducted using magic‐angle spinning 13C, 15N and 1H NMR spectroscopy, together with first‐principles computations of NMR shielding (including use of a program that takes explicit account of the translational symmetry inherent in crystalline structures). The effects on 13C chemical shifts of side‐chain rotations have been explored. Information derived from these studies was then incorporated within a systematic space‐search methodology for elucidation of trial crystallographic structures from powder XRD. Copyright © 2006 John Wiley & Sons, Ltd.
Stability constants: comparative study of fitting methods. Determination of second‐order complexation constants by23Na and7Li NMR chemical shift titration
Authors: Masiker Marilyn C. , Mayne Charles L. , Eyring Edward M.
Published: February 2006

NMR chemical shift titration has been widely used as a method for the determination of stability constants. Systems involving metal‐ligand complexation have been investigated using a number of methodologies. There are significant differences in the values reported for stability constants obtained by different experimental methods, such as calorimetry and ion selective electrode (ISE) titrations; nor has NMR chemical shift titration always yielded consistent results. Different researchers have obtained different results for the same system with results differing by as much as an order of magnitude. The chemical shift data are generally plotted against the concentration ratio of the metal and ligand for a set of solutions. A nonlinear least squares fitting method using an analytical solution of the cubic equation for the equilibrium concentration of the free ligand is used in this study and compared with methods used in the literature. Second‐order association constants for the LiClO4:12‐crown‐4 system in acetonitrile and the NaClO4:12‐crown‐4 system in methanol are reported. Formation of both 1:1 and 1:2 metal‐ligand complexes are considered. The LiClO4:12‐crown‐4 acetonitrile system had been investigated previously by NMR titration but only 1:1 complexation was considered in that study. This study provides convincing evidence that both 1:1 and 1:2 complexes are important, at least, in the lithium system. A Monte Carlo investigation of the propagation of errors from the chemical shifts to the stability constants shows that the choice of data analysis methods may, in part, contribute to discrepancies and that the nonlinear nature of the model can dramatically affect the error limits on the stability constants. Copyright © 2006 John Wiley & Sons, Ltd.
A broad‐spectrum fluorescence‐based peptide library for the rapid identification of protease substrates
Authors: Thomas Daniel A. , Francis Peter , Smith Carla , Ratcliffe Steven , Ede Nicholas J. , Kay Corinne , Wayne Gareth , Martin Steve L. , Moore Keith , Amour Augustin , Hooper Nigel M.
Published: February 2006

Identification of peptide substrates for proteases can be a major undertaking. To overcome issues such as feasibility and deconvolution, associated with large peptide libraries, a ‘small but smart’ generic fluorescence resonance energy transfer rapid endopeptidase profiling library (REPLi) was synthesised as a tool for rapidly identifying protease substrates. Within a tripeptide core, flanked by Gly residues, similar amino acids were paired giving rise to a relatively small library of 3375 peptides divided into 512 distinct pools each containing only 8 peptides. The REPLi was validated with trypsin, pepsin, the matrix metalloprotease (MMP)‐12 and MMP‐13 and calpains‐1 and ‐2. In the case of calpain‐2, a single iteration step involving LC‐MS, provided the definitive residue specificity from which a highly sensitive fluorogenic substrate, (FAM)‐Gly‐Gly‐Gly‐Gln‐Leu‐Tyr‐Gly‐Gly‐DPA‐Arg‐Arg‐Lys‐(TAMRA), was then designed. The thorough validation of this ‘small but smart’ peptide library with representatives from each of the four mechanistic protease classes indicates that the REPLi will be useful for the rapid identification of substrates for multiple proteases.
Is significant cystic fibrosis‐related liver disease a risk factor in the development of bone mineralization abnormalities?
Authors: Alex George , Catto‐Smith Anthony G. , Ditchfield Michael , Roseby Robert , Robinson Philip J. , Cameron Fergus J. , Oliver Mark R.
Published: February 2006

In order to assess the effects of significant cystic fibrosis‐related liver disease (CFLD) on bone health, we compared the bone mineral status of older children and adolescents with CFLD to those with cystic fibrosis (CF) alone. Thirteen children (age range, 10–19 years) from our clinical CF services were identified with significant CFLD (9 of these 13 patients had clinical and radiological evidence of portal hypertension). This cohort was then matched by age, gender, and anthropometric measurements with equal numbers of patients with CF alone. All patients had a dual‐energy X‐ray absorptiometry (DEXA) scan to determine bone mineral content (BMC), bone area (BA), bone mineral density (BMD), and bone mineral apparent density (BMAD) in the region of the lumbar spine. Blood was drawn to determine serum vitamin A, D, E, and K status and liver function tests. The best forced expired volume in 1 sec (FEV1) for each patient in the 12 months around the time of the scan was also documented. Patients with CFLD had slightly worse FEV1 (82 ± 20% vs. 91 ± 16%, P = 0.05) and significantly higher alanine aminotransferase (65.5 ± 35 IU/l vs. 30 ± 20 IU/l, P = 0.01) than those with CF alone. The mean lumbar spine BA, BMC, BMD, and BMAD were not different between children with CFLD and CF. In conclusion, the presence of significant liver disease in children with CF does not appear to be an additional risk factor for the development of abnormal bone mineralization. Pediatr Pulmonol. © 2006 Wiley‐Liss, Inc.
Factors influencing gender differences in the diagnosis and treatment of asthma in childhood: The Tucson Children's Respiratory Study
Authors: Wright Anne L. , Stern Debra A. , Kauffmann Francine , Martinez Fernando D.
Published: February 2006

Studies identified gender differences in diagnosed asthma, but the extent to which they can be attributed to differences in symptom experience and frequency rather than factors influencing diagnosis has not been established. We investigated prevalence of, and consultation for, asthma symptoms, as well as diagnosis and treatment in 533 boys and 556 girls enrolled in the Tucson Children's Respiratory Study, a population‐based birth‐cohort study. Questionnaires regarding respiratory symptoms and diagnoses were obtained at ages 2, 3, 6, 8, 11, 13, 16, and 18 years. Boys were significantly more likely than girls to experience both wheeze and frequent wheeze most years in the first decade of life. However, girls with symptoms were less likely than boys to see a physician (74.1% vs. 83.4%, P < 0.001) and to be labeled as having asthma (43.3% vs. 53.8%, P < 0.009), even after adjusting for symptom frequency. A difference in symptom presentation also appeared to influence diagnosis: nocturnal cough without frequent wheeze was more prevalent among girls, and was associated with reduced diagnosis of asthma. Among subjects who consulted a physician for wheeze, boys were significantly more likely than girls to have taken medication (81.5% vs. 73.5%, P < 0.01). The lag time between age at first wheeze and first use of medication among those consulting a physician for wheeze or asthma was greater for girls, especially among subjects with frequent wheeze (2.8 vs. 1.6 years, P < 0.005). These findings indicate that gender differences in the diagnosis and treatment of asthma cannot be explained completely by differences in symptom prevalence and frequency. Pediatr Pulmonol. © 2006 Wiley‐Liss, Inc.
Automated method for measuring globin adducts of acrylamide and glycidamide at optimized Edman reaction conditions
Authors: Vesper Hubert W. , Ospina Maria , Meyers Tunde , Ingham Leigha , Smith Antoinette , Gray J. Gibson , Myers Gary L.
Published: February 2006

The general population is exposed to acrylamide, a potential human carcinogen, through food and cigarette smoke. The assessment of human exposure to acrylamide is important in the evaluation of health risks associated with this chemical. Hemoglobin adducts of acrylamide (AA‐Hb) and its primary metabolite glycidamide (GA‐Hb) are established biomarkers of acrylamide exposure and methods to measure these biomarkers using modified Edman reaction are described. Only limited information about the optimal Edman reaction conditions such as pH or temperature is available for these adducts and the existing methods do not allow automation needed in biomonitoring studies. In this study, the yield of Edman products of AA‐Hb and GA‐Hb between pH 3–10 and at 35–55°C at different time intervals, and the applicability of liquid‐liquid extraction on diatomaceous earth for analyte extraction, were assessed and results were used in a new optimized method. The applicability of our optimized method was assessed by comparing results obtained with a convenience sample from 96 individuals with a conventional method. Maximum yield of Edman products was obtained between pH 6–7, heating the reaction solution at 55°C for 2 h resulted in the same yields as with conventional conditions, and use of diatomaceous earth was found suitable for automated analyte extraction. Using these conditions, no difference was observed between our optimized and a conventional method. The median globin adduct values in the convenience sample are 129 pmol/g globin (range: 27–453 pmol/g globin) and 97 pmol/g globin (range: 27–240 pmol/g globin) for AA‐Hb and GA‐Hb, respectively. The GA‐Hb/AA‐Hb ratio decreases significantly with increasing AA‐Hb values indicating that measurement of AA‐Hb as well as GA‐Hb are needed to appropriately assess human exposure to acrylamide. Published in 2006 by John Wiley & Sons, Ltd.
Fragmentation study of protonated chalcones by atmospheric pressure chemical ionization and tandem mass spectrometry
Authors: Tai Yuanpo , Pei Saifeng , Wan Jieping , Cao Xiaoji , Pan Yuanjiang
Published: February 2006

Fragmentation mechanisms of protonated chalcone and its derivatives with different functional groups were investigated by atmospheric pressure chemical ionization with tandem mass spectrometry (MS/MS). The major fragmentation pathways were loss of the phenyl group from the A or B ring, combined with loss of CO. Losses of H2O and CO from the precursor ions of [M+H]+ are proposed to occur via rearrangements. Elimination of water from protonated chalcones was observed in all the title compounds to yield a stable ion but it was difficult to obtain skeletal fragmentation of a precursor ion. Loss of CO was found in the MS/MS spectra of all the compounds except the nitro‐substituted chalcones. When the [M+HCO]+ ion was fragmented in the MS/MS experiments, there were distinctive losses of 15 and 28 Da, as the methyl radical and ethylene, respectively. The ion at m/z 130, found only in the nitro‐substituted chalcones, was assigned as C9H6O by Fourier transform ion cyclotron resonance (FTICR)‐MS/MS; m/z 130 is a common fragment ion in the electron ionization (EI) spectra of chalcones. In order to more easily distinguish the constitutional isomers of these chalcones, breakdown curves were produced and these provided strong support in this study. Copyright © 2006 John Wiley & Sons, Ltd.
Interval estimates for the ratio and difference of two lognormal means
Authors: Chen Yea‐Hung , Zhou Xiao‐Hua
Published: February 2006

Health research often gives rise to data that follow lognormal distributions. In two sample situations, researchers are likely to be interested in estimating the difference or ratio of the population means. Several methods have been proposed for providing confidence intervals for these parameters. However, it is not clear which techniques are most appropriate, or how their performance might vary. Additionally, methods for the difference of means have not been adequately explored. We discuss in the present article five methods of analysis. These include two methods based on the log‐likelihood ratio statistic and a generalized pivotal approach. Additionally, we provide and discuss the results of a series of computer simulations. Finally, the techniques are applied to a real example. Copyright © 2006 John Wiley & Sons, Ltd.
Analysis of repeated bouts of measurements in the framework of generalized estimating equations
Authors: Shults Justine , Mazurick Carissa A. , Richard Landis J.
Published: February 2006

We consider a longitudinal study of interstitial cystitis (IC) in women, in which the time between bouts of repeated measurements is large relative to the within‐bout separation in time. Our outcome of interest is the number of nocturnal voids that we model via quasi‐least squares (QLS) in the framework of generalized estimating equations (GEE). To account for potential intra‐subject correlation, we directly apply a banded Toeplitz correlation structure that previously was only implemented in anad hocapproach using GEE. We describe this structure, its appropriateness for data from the IC study, and the results of our analysis. We then demonstrate that correct specification of the underlying correlation structureversusincorrectly applying a simpler structure can prevent substantial losses in efficiency in estimation of the regression parameter. These comparisons involve the limiting values of the estimates of the correlation parameters, which are not consistent for the misspecification scenarios considered here. We therefore obtain the limiting values of the QLS estimates when the structure is incorrectly specified. Copyright © 2006 John Wiley & Sons, Ltd.
Joint estimation of time‐dependent and non‐linear effects of continuous covariates on survival
Authors: Abrahamowicz Michal , MacKenzie Todd A.
Published: February 2006

In order to yield more flexible models, the Cox regression model, λ(t;x) = λ0(t)exp(βx), has been generalized using different non‐parametric model estimation techniques. One generalization is the relaxation of log‐linearity inx, λ(t;x) = λ0(t)exp[r(x)]. Another is the relaxation of the proportional hazards assumption, λ(t;x) = λ0(t)exp[β(t)x]. These generalizations are typically considered independently of each other. We propose the product model, λ(t;x) = λ0(t)exp[β(t)r(x)] which allows for joint estimation of both effects, and investigate its properties. The functions describing the time‐dependent β(t) and non‐linearr(x) effects are modelledsimultaneouslyusing regression splines and estimated by maximum partial likelihood. Likelihood ratio tests are proposed to compare alternative models. Simulations indicate that both the recovery of the shapes of the two functions and the size of the tests are reasonably accurate provided they are based on the correct model. By contrast, type I error rates may be highly inflated, and the estimates considerably biased, if the model is misspecified. Applications in cancer epidemiology illustrate how the product model may yield new insights about the role of prognostic factors. Copyright © 2006 John Wiley & Sons, Ltd.
Monitoring medical procedures by exponential smoothing
Authors: Spliid Henrik
Published: February 2006

A new exponentially weighted moving average (EWMA) control chart well suited for ‘online’ routine surveillance of medical procedures is introduced. The chart is based on inter‐event counts for failures recorded when the failures occur. The method can be used for many types of hospital procedures and activities, such as problems or errors in surgery, hospital‐acquired infections, erroneous handling or prescription of medicine, deviations from scheduled treatments causing inconveniences for patients. The construction, the use and the effectiveness of the control chart are demonstrated by two well‐known examples about wound infection in orthopaedic surgery and neonatal arterial switch surgery. The method is easy to implement and apply, it illustrates, estimates and tests the current failure rate. Comparisons with two examples from the literature indicate that its ability to quickly detect an increased failure rate is comparable to that of other well‐established methods. Copyright © 2006 John Wiley & Sons, Ltd.
Key concepts in modeling product development processes
Authors: Browning Tyson R. , Fricke Ernst , Negele Herbert
Published: February 2006

This paper provides a foundation for modeling the set of activities and their relationships by which systems are engineered, or, more broadly, by which products and services are developed. It provides background, motivations, and formal definitions for process modeling in this specialized environment. We treat the process itself as a kind of system that can be engineered. However, while product systems must be created, the process systems for developing complex products must, to a greater extent, be discovered and induced. Then, they tend to be reused, either formally as standard processes, or informally by the workforce. We distinguish and clarify several important concepts in modeling processes, including: product development versus repetitive business processes, descriptive versus prescriptive processes, activities as actions versus deliverables as interactions, standard versus deployed processes, centralized versus decentralized process modeling, “as is” versus “to be” process modeling, and multiple phases in product development. We also present a basically simple yet highly extendable and generalized framework for modeling product development processes. The framework enables building a single model to support a variety of purposes, including project planning (scheduling, budgeting, resource loading, and risk management) and control, and it provides the scaffolding for knowledge management and organizational learning, among numerous other uses. © 2006 Wiley Periodicals, Inc. Syst Eng 9: 104–128, 2006
Efficient Nonparametric Approaches for Estimating the Operating Characteristics of Discrete Item Responses
Authors: Samejima Fumiko
Published: February 2006

Rationale and the actual procedures of two nonparametric approaches, called Bivariate P.D.F. Approach and Conditional P.D.F. Approach, for estimating the operating characteristic of a discrete item response, or the conditional probability, given latent trait, that the examinee's response be that specific response, are introduced and discussed. These methods are featured by the facts that: (a) estimation is made without assuming any mathematical forms, and (b) it is based upon a relatively small sample of several hundred to a few thousand examinees.

Some examples of the results obtained by the Simple Sum Procedure and the Differential Weight Procedure of the Conditional P.D.F. Approach are given, using simulated data. The usefulness of these nonparametric methods is also discussed.
Tests for Linear Trend in the Smallest Eigenvalues of the Correlation Matrix
Authors: Bentler Peter M. , Yuan Ke-Hai
Published: February 2006

A test for linear trend among a set of eigenvalues of a correlation matrix is developed. As a technical implementation of Cattell's scree test, this is a generalization of Anderson's test for the equality of eigenvalues, and extends Bentler and Yuan's work on linear trends in eigenvalues of a covariance matrix. The power of minimum x2 and maximum likelihood ratio tests are compared. Examples show that the linear trend hypothesis is more realistic than the standard hypothesis of equality of eigenvalues, and that the hypothesis is compatible with standard decisions on the number of factors or components to retain in data analysis.
Fitting Multivariage Normal Finite Mixtures Subject to Structural Equation Modeling
Authors: Dolan Conor V. , van der Maas Han L. J.
Published: February 2006

This paper is about fitting multivariate normal mixture distributions subject to structural equation modeling. The general model comprises common factor and structural regression models. The introduction of covariance and mean structure models reduces the number of parameters to be estimated in fitting the mixture and enables one to investigate a variety of substantive hypotheses concerning the differences between the components in the mixture. Within the general model, individual parameters can be subjected to equality, nonlinear and simple bounds constraints. Confidence intervals are based on the inverse of the Hessian and on the likelihood profile. Several illustrations are given and results of a simulation study concerning the confidence intervals are reported.
The Second Order Approximation to Sample Influence Curve in Canonical Correlation Analysis
Authors: Fung Wing K. , Gu Hong
Published: February 2006

A second order approximation to the sample influence curve (SIC) in canonical correlation analysis has been derived in the literature. However, it does not seem satisfactory for some cases. In this paper, we present a more accurate second order approximation. As a particular case, the proposed method is exact for the SIC of the squared multiple correlation coefficient. An example is given.
A Bayesian Approach to Nonlinear Latent Variable Models using the Gibbs Sampler and the Metropolis-Hastings Algorithm
Authors: Arminger Gerhard , Muthén Bengt O.
Published: February 2006

Nonlinear latent variable models are specified that include quadratic forms and interactions of latent regressor variables as special cases. To estimate the parameters, the models are put in a Bayesian framework with conjugate priors for the parameters. The posterior distributions of the parameters and the latent variables are estimated using Markov chain Monte Carlo methods such as the Gibbs sampler and the Metropolis-Hastings algorithm. The proposed estimation methods are illustrated by two simulation studies and by the estimation of a non-linear model for the dependence of performance on task complexity and goal specificity using empirical data.
Data, Model, Conclusion, Doing it Again
Authors: Molenaar Ivo W.
Published: February 2006

This paper explores the robustness of conclusions from a statistical model against variations in model choice (rather than variations in random sampling and random assignment to treatments, which are the usual variations covered by inferential statistics). After the problem formulation in section 1, section 2 presents an example from Box and Tiao in which variation in parent distribution is modeled for a one sample location problem. An adaptive Bayesian procedure permits to use a weighted mixture of parent distributions rather than choosing just one, such as a normal or a uniform distribution.

In section 3 similar considerations are applied to an event history model for the influence of education and gender on age at first marriage, but here the conclusions are hardly influenced by the choice of the duration distribution. In section 4 a brief discussion of model choice in factor analysis and structural equation models is followed by a more elaborate treatment of the choice of integer valued slopes for item response functions in the OPLM model which is an extension of the Rasch model. A modest simulation study suggests that Adaptive Bayesian Modeling with a mixture of sets of slopes works better than fixing one set of postulated slopes.

The paper concludes with some remarks on the roles and sources of prior distributions followed by a short epilogue which argues that simultaneous consideration of a class of models for the same data is sometimes superior to exclusively analyzing the data under one specific model chosen from such a class.
Graph-Theoretic Representations for Proximity Matrices Through Strongly-Anti-Robinson or Circular Strongly-Anti-Robinson Matrices
Authors: Hubert Lawrence , Arabie Phipps , Meulman Jacqueline
Published: February 2006

There are various optimization strategies for approximating, through the minimization of a least-squares loss function, a given symmetric proximity matrix by a sum of matrices each subject to some collection of order constraints on its entries. We extend these approaches to include components in the approximating sum that satisfy what are called the strongly-anti-Robinson (SAR) or circular strongly-anti-Robinson (CSAR) restrictions. A matrix that is SAR or CSAR is representable by a particular graph-theoretic structure, where each matrix entry is reproducible from certain minimum path lengths in the graph. One published proximity matrix is used extensively to illustrate the types of approximation that ensue when the SAR or CSAR constraints are imposed.
Observed-Score Equating as a Test Assembly Problem
Authors: van der Linden Wim J. , Luecht Richard M.
Published: February 2006

A set of linear conditions on item response functions is derived that guarantees identical observed-score distributions on two test forms. The conditions can be added as constraints to a linear programming model for test assembly that assembles a new test form to have an observed-score distribution optimally equated to the distribution on an old form. For a well-designed item pool and items fitting the IRT model, use of the model results into observed-score pre-equating and prevents the necessity of post hoc equating by a conventional observed-score equating method. An empirical example illustrates the use of the model for an item pool from the Law School Admission Test.
A MCMC-Method for Models with Continuous Latent Responses
Authors: Maris Gunter , Maris Eric
Published: February 2006

This paper introduces a new technique for estimating the parameters of models with continuous latent data. Using the Rasch model as an example, it is shown that existing Bayesian techniques for parameter estimation, such as the Gibbs sampler, are not always easy to implement. Then, a new sampling-based Bayesian technique, called the DA-T-Gibbs sampler, is introduced. The DA-T-Gibbs sampler relies on the particular latent data structure of latent response models to simplify the computations involved in parameter estimation.
Transforming Three-Way Arrays to Maximal Simplicity
Authors: Rocci Roberto , ten Berge Jos M. F.
Published: February 2006

Transforming the core array in Tucker three-way component analysis to simplicity is an intriguing way of revealing structures in between standard Tucker three-way PCA, where the core array is unconstrained, and CANDECOMP/PARAFAC, where the core array has a generalized diagonal form. For certain classes of arrays, transformations to simplicity, that is, transformations that produce a large number of zeros, can be obtained explicitly by solving sets of linear equations. The present paper extends these results. First, a method is offered to simplifyJ ×J × 2 arrays. Next, it is shown that the transformation that simplifies anI ×J ×K array can be used to also simplify the (complementary) arrays of order (JK −I) ×J ×K, of orderI × (IK −J) ×K and of orderI ×J × (IJ −K). Finally, the question of what constitutes the maximal simplicity for arrays (the maximal number of zero elements) will be considered. It is shown that cases of extreme simplicity, considered in the past, are, in fact, cases of maximal simplicity.
Hypergeometric Family and Item Overlap Rates in Computerized Adaptive Testing
Authors: Chang Hua-Hua , Zhang Jinming
Published: February 2006

A computerized adaptive test (CAT) is usually administered to small groups of examinees at frequent time intervals. It is often the case that examinees who take the test earlier share information with examinees who will take the test later, thus increasing the risk that many items may become known. Item overlap rate for a group of examinees refers to the number of overlapping items encountered by these examinees divided by the test length. For a specific item pool, different item selection algorithms may yield different item overlap rates. An important issue in designing a good CAT item selection algorithm is to keep item overlap rate below a preset level. In doing so, it is important to investigate what the lowest rate could be for all possible item selection algorithms. In this paper we rigorously prove that if every item has an equal possibility to be selected from the pool in a fixed-length CAT, the number of overlapping items among any α randomly sampled examinees follows the hypergeometric distribution family for α ≥ 1. Thus, the expected values of the number of overlapping items among any randomly sampled α examinees can be calculated precisely. These values may serve as benchmarks in controlling item overlap rates for fixed-length adaptive tests.
Influence Analysis of Ranking Data
Authors: Poon Wai-Yin , Chan Wai
Published: February 2006

This paper develops diagnostic measures to identify those observations in Thurstonian models for ranking data which unduly influence parameter estimates that are obtained by the partition maximum likelihood approach of Chan and Bentler (1998). Diagnostic measures are constructed by employing the local influence approach that uses geometric techniques to assess the effect of small perturbations on a postulated statistical model. Very little additional effort is required to compute the proposed diagnostic measures, because all of the necessary building blocks are readily available after a usual fit of the model.
Latent Change Classes in Dichotomous Data
Authors: Formann Anton K. , Ponocny Ivo
Published: February 2006

Changes in dichotomous data caused by treatments can be analyzed by means of the so-called linear logistic model with relaxed assumptions (LLRA). The LLRA does not require observable criteria representing a single underlying latent trait, but it postulates the generalizability of the treatment effects over criteria and subjects. To test this latter crucial assumption, the mixture LLRA was proposed that allows directly unobservable types of subjects to have different treatment effects. As the earlier methods for estimating the parameters of the mixture LLRA have specific drawbacks, a further method based on the conditional maximum likelihood principle will be presented here. In contrast to the earlier conditional methods, it uses all of the dichotomous change data while having fewer parameters. Further, its goodness-of-fit tests become more sensitive to a falsely specified number of change-types even though the treatment effects are biased. For typically occurring small to moderate sample sizes, however, parametric bootstrapping of the distributions of the fit statistics is recommended for performing hypotheses tests. Finally, three applications of the new method to empirical data are described: first, about the effect of the so-called Trager psychophysical integration, second, about the effect of autogenic therapy on patients with psychosomatic symptoms, and, third, about the effect of religious education on the attitude towards sects.
A Branch-and-Bound Algorithm for Fitting Anti-Robinson Structures to Symmetric Dissimilarity Matrices
Authors: Brusco Michael J.
Published: February 2006

The seriation of proximity matrices is an important problem in combinatorial data analysis and can be conducted using a variety of objective criteria. Some of the most popular criteria for evaluating an ordering of objects are based on (anti-) Robinson forms, which reflect the pattern of elements within each row and/or column of the reordered matrix when moving away from the main diagonal. This paper presents a branch-and-bound algorithm that can be used to seriate a symmetric dissimilarity matrix by identifying a reordering of rows and columns of the matrix optimizing an anti-Robinson criterion. Computational results are provided for several proximity matrices from the literature using four different anti-Robinson criteria. The results suggest that with respect to computational efficiency, the branch-and-bound algorithm is generally competitive with dynamic programming. Further, because it requires much less storage than dynamic programming, the branch-and-bound algorithm can provide guaranteed optimal solutions for matrices that are too large for dynamic programming implementations.
A Multidimensional Item Response Model: Constrained Latent Class Analysis Using the Gibbs Sampler and Posterior Predictive Checks
Authors: Hoijtink Herbert , Molenaar Ivo W.
Published: February 2006

In this paper it will be shown that a certain class of constrained latent class models may be interpreted as a special case of nonparametric multidimensional item response models. The parameters of this latent class model will be estimated using an application of the Gibbs sampler. It will be illustrated that the Gibbs sampler is an excellent tool if inequality constraints have to be taken into consideration when making inferences. Model fit will be investigated using posterior predictive checks. Checks for manifest monotonicity, the agreement between the observed and expected conditional association structure, marginal local homogeneity, and the number of latent classes will be presented.
Approximating the Conditional Distribution of Person Fit Indexes for Checking the Rasch Model
Authors: Bedrick Edward J.
Published: February 2006

We present a simple approximation to the conditional distribution of goodness-of-fit statistics for the Rasch model, assuming that the item difficulties are known. The approximation is easily programmed, and gives relatively accurate assessments of conditional p-values for tests of length 10 or more. A few generalizations are discussed.
A Unifying Expression for the Maximal Reliability of a Linear Composite
Authors: Li Heng
Published: February 2006

A formally simple expression for the maximal reliability of a linear composite is provided, its theoretical implications and its relation to existing results for reliability are discussed.
Weighted Least Squares Fitting Using Ordinary Least Squares Algorithms
Authors: Kiers Henk A. L.
Published: February 2006

A general approach for fitting a model to a data matrix by weighted least squares (WLS) is studied. This approach consists of iteratively performing (steps of) existing algorithms for ordinary least squares (OLS) fitting of the same model. The approach is based on minimizing a function that majorizes the WLS loss function. The generality of the approach implies that, for every model for which an OLS fitting algorithm is available, the present approach yields a WLS fitting algorithm. In the special case where the WLS weight matrix is binary, the approach reduces to missing data imputation.
Dynamic Factor Analysis of Nonstationary Multivariate Time Series
Authors: Molenaar Peter C. M. , De Gooijer Jan G. , Schmitz Bernhard
Published: February 2006

A dynamic factor model is proposed for the analysis of multivariate nonstationary time series in the time domain. The nonstationarity in the series is represented by a linear time dependent mean function. This mild form of nonstationarity is often relevant in analyzing socio-economic time series met in practice. Through the use of an extended version of Molenaar's stationary dynamic factor analysis method, the effect of nonstationarity on the latent factor series is incorporated in the dynamic nonstationary factor model (DNFM). It is shown that the estimation of the unknown parameters in this model can be easily carried out by reformulating the DNFM as a covariance structure model and adopting the ML algorithm proposed by Jöreskog. Furthermore, an empirical example is given to demonstrate the usefulness of the proposed DNFM and the analysis.