bluuebunny/crossref_metadata_2025 huggingface dataset:
Aromatic side‐chain interactions in proteins. II. Near‐ and far‐sequence Phe‐X pairs
Authors: Thomas Annick , Meurisse Rita , Brasseur Robert
Published: October 2002

We have collected all aromatic pairs (3152) involving an N‐phenyl partner in a dataset of 593 proteins of the PDB: 728 of these pairs involve a partner residue less than 6 apart in the sequence. These near‐sequence Phe‐X pairs correspond to specific conformations that stabilize secondary structures, mainly α‐helices when the residues are 1, 3, and 4 apart, and β‐strands when they are 2 apart in the sequence. These conformations are not spatially random and have been examined in detail. The remaining phenylalanine pairs (2424) are between partners more than 5 apart in the sequence. Of these far‐sequence pairs, 34% of occurrences are in sheets. Next in frequencies are pairs that bridge a β‐strand to a helix (24%), followed by pairs that bridge a β‐strand to a random coiled structure (15%). Helix to helix pairs only constitute 12% of these far‐sequence pairs. Analysis of the pairing frequency supports the hypothesis that aromatic interactions are late events of protein folding. Proteins 2002;48:635–644. © 2002 Wiley‐Liss, Inc.
Distinguishing foldable proteins from nonfolders: When and how do they differ?
Authors: Sosnick Tobin R. , Berry R. Stephen , Colubri Andrés , Fernández Ariel
Published: October 2002

When a denatured polypeptide is put into refolding conditions, it undergoes conformational changes on a variety of times scales. We set out here to distinguish the fast events that promote productive folding from other processes that may be generic to any non‐folding polypeptide. We have apply an ab initio folding algorithm to model the folding of various proteins and their compositionally identical, random‐sequence analogues. In the earliest stages, proteins and their scrambled‐sequence counterparts undergo indistinguishable reductions in the extent to which they explore conformation space. For both polypeptides, an early contraction occurs but does not involve the formation of a distinct intermediate. Following this phase, however, the naturally‐occurring sequences are distinguished by an increase in the formation of three‐body correlations wherein a hydrophobic group desolvates and protects an intra‐molecular hydrogen bond. These correlations are manifested in a mild but measurable reduction of the accessible configuration space beyond that of the random‐sequence peptides, and portend the folding to the native structure. Hence, early events reflect a generic response of the denatured ensemble to a change in solvent condition, but the wild‐type sequence develops additional correlations as its structure evolves that can reveal the protein's foldability. Proteins 2002;49:15–23. © 2002 Wiley‐Liss, Inc.
Crystal structures of unligated and CN‐ligated Glycera dibranchiata monomer ferric hemoglobin components III and IV
Authors: Park Ha‐Jeung , Yang Cheng , Treff Nathan , Satterlee James D. , Kang ChulHee
Published: October 2002

Erythrocytes of the marine annelid, Glycera dibranchiata, contain a mixture of monomeric and polymeric hemoglobins. There are three major monomer hemoglobin components, II, III, IV (also called GMH2, 3, and 4), that have been highly purified and well characterized. We have now crystallized GMH3 and GMH4 and determined their structures to 1.4–1.8 Å resolution. The structures were determined for these two monomer hemoglobins in the oxidized (Fe3+, ferric, or met‐) forms in both the unligated and cyanide‐ligated states. This work differs from two published, refined structures of a Glycera dibranchiata monomer hemoglobin, which has a sequence that is substantially different from any bona fide major monomer hemoglobins (GMH2, 3, or 4). The high‐resolution crystal structures (presented here) and the previous NMR structure of CO‐ligated GMH4, provide a basis for interpreting structure/function details of the monomer hemoglobins. These details include: (1) the strong correlation between temperature factor and NMR dynamics for respective protein forms; (2) the unique nature of the HisE7Leu primary sequence substitutions in GMH3 and GMH4 and their impact on cyanide ion binding kinetics; (3) the LeuB10Phe difference between GMH3 and GMH4 and its impact on ligand binding; and (4) elucidation of changes in the structural details of the distal and proximal heme pockets upon cyanide binding. Proteins 2002;49:49–60. © 2002 Wiley‐Liss, Inc.
Sub‐lethal effects of deltamethrin on walking behaviour and response to host kairomone of the egg parasitoid Trissolcus basalis
Authors: Salerno Gianandrea , Colazza Stefano , Conti Eric
Published: October 2002

The lethal doses of the pyrethroid deltamethrin were estimated for the egg parasitoid Trissolcus basalis (Wollaston) (Hymenoptera: Scelionidae), and the sub‐lethal effects of an LD25 on female walking behaviour were evaluated. Linear speed of treated parasitoids was reduced compared with that of untreated ones for a period of up to 24 h. The sub‐lethal effects of deltamethrin on parasitoid response to patches contaminated by a contact kairomone from its host, Nezara viridula L (Heteroptera: Pentatomidae), was also evaluated. Both treated and untreated parasitoids responded to host‐contaminated patches by increasing residence time and decreasing linear speed. However, treated females showed a significantly lower residence time compared with untreated females. Both treated and untreated females showed a similar decrease over time in the proportion of time spent in the host‐contaminated patch. Hence, we hypothesise that the sub‐lethal effect of deltamethrin on host foraging may decrease T basalis efficacy in controlling N viridula.

© 2002 Society of Chemical Industry
Human platelet aggregation inhibitors from thyme (Thymus vulgaris L.)
Authors: Okazaki Kenji , Kawazoe Kazuyoshi , Takaishi Yoshihisa
Published: October 2002

Two antiaggregant compounds, thymol (compound 1) and 3,4,3′,4′‐tetrahydroxy‐5,5′‐diisopropyl‐2,2′‐dimethylbiphenyl (compound 2) were isolated from the leaves of thyme (Thymus vulgaris L.). The structures were determined by 1H‐, 13C‐NMR and mass spectra (MS) studies. These compounds inhibited platelet aggregation induced by collagen, ADP, arachidonic acid (AA) and thrombin except that compound 2 did not inhibit platelet aggregation induced by thrombin. Copyright © 2002 John Wiley & Sons, Ltd.
Computer program for calculating the p‐value in testing process capability index Cpmk
Authors: Pearn W. L. , Lin P. C.
Published: October 2002

Many process capability indices, including Cp, Cpk, and Cpm, have been proposed to provide numerical measures on the process potential and performance. Combining the advantages of these indices, Pearn et al. (1992) introduced a new capability index called Cpmk, which has been shown to be a useful capability index for processes with two‐sided specification limits. In this paper, we implement the theory of a testing hypothesis using the natural estimator of Cpmk, and provide an efficient Maple computer program to calculate the p‐values. We also provide tables of the critical values for some commonly used capability requirements. Based on the test we develop a simple step‐by‐step procedure for in‐plant applications. The practitioners can use the proposed procedure to determine whether their process meets the preset capability requirement, and make reliable decisions. Copyright © 2002 John Wiley & Sons, Ltd.
Transient behavior of time‐between‐failures of complex repairable systems
Authors: Keats J. Bert , Chambal Stephen P.
Published: October 2002

It is well known for complex repairable systems (with as few as four components), regardless of the time‐to‐failure (TTF) distribution of each component, that the time‐between‐failures (TBFs) tends toward the exponential. This is a long‐term or ‘steady‐state’ property. Aware of this property, many of those modeling such systems tend to base spares provisioning, maintenance personnel availability and other decisions on an exponential TBFs distribution. Such a policy may suffer serious drawbacks. A non‐homogeneous Poisson process (NHPP) accounts for these intervals for some time prior to ‘steady‐state’. Using computer simulation, the nature of transient TBF behavior is examined. The number of system failures until the exponential TBF assumption is valid is of particular interest. We show, using a number of system configurations and failure and repair distributions, that the transient behavior quickly drives the TBF distribution to the exponential. We feel comfortable with achieving exponential results for the TBF with 30 system failures. This number may be smaller for configurations with more components. However, at this point, we recommend 30 as the systems failure threshold for using the exponential assumption. Copyright © 2002 John Wiley & Sons, Ltd.
An analysis of the effect of a reliability paradigm shift on leading British aerospace companies
Authors: Jones J. A. , Warrington L.
Published: October 2002

The aerospace industry is moving towards a new paradigm for the statement of reliability specifications. This paradigm is not a technical metric inherent to a system in isolation, but rather encompasses the wider objectives, operational profile and logistic priorities of its customer. This customer focus is encapsulated in the metrics Failure Free Operating Period and Maintenance Free Operating Period. These metrics describe the duration of effective system operation, in the first case for systems where faults and maintenance are permitted and in the second for systems where faults may not be repaired. As part of the Department of Trade and Industry (DTI) funded Aerospace Project for Insertion of Reliability (ASPIRE) research programme, which itself is part of the Ultra Reliable Aircraft (URA) programme, representatives of leading aerospace companies were interviewed about their opinion n how this new reliability paradigm and associated concepts would affect their way of doing business and their engineering processes. It would appear that the aerospace industry is ready for a move to a more realistic set of reliability metrics and away from the old style MTBF based metrics. This sea change would most likely be welcomed by customers, but as yet the manufacturing companies are unconvinced that such a radical move would be a good thing. Much of the resistance to change is due to old‐fashioned, but well entrenched, beliefs in the traditional way of doing things. A move away from this would bring freshness to the industry and lead to cost and time savings as the traditional approach is dropped in favour of a more planned and thought out approach. Copyright © 2002 John Wiley & Sons, Ltd.
VB2000: Pushing valence bond theory to new limits
Authors: Li Jiabo , McWeeny Roy
Published: October 2002

Full valence bond (VB) calculations for a system of N electrons have always been hindered by the rapidly growing value of N!, which effectively imposes a limit N < 20. Often, however, not all electrons in a molecule are of interest; if we focus on a “group” G of NG electrons (e.g., in an “active” region), then it is NG! that sets the limit. In this work, group function (GF) theory is used to represent a molecule as a collection of interacting electron groups, each with a many‐electron wave function of any chosen form (e.g., VB, MO‐SCF, MCSCF), and each GF is optimized individually in a step‐by‐step process. An efficient VB algorithm allows for up to 14 electrons in any VB group and this combination of GF and VB methods greatly extends the range of feasibility of molecular calculations with VB‐type wave functions: Thus, (1) a large system can be divided into any number of smaller subsystems (groups); (2) each group may contain any chosen number of electrons; (3) the form of any group function (including its level of accuracy) may be chosen at will by the program user. A number of sample calculations are briefly presented. © 2002 Wiley Periodicals, Inc. Int J Quantum Chem, 2002
The Dirac equation in the algebraic approximation: VIII. Comparison of finite basis set and finite element molecular Dirac–Hartree–Fock calculations for the H2, LiH, and BH ground states
Authors: Quiney H. M. , Glushkov V. N. , Wilson S.
Published: October 2002

Using basis sets of distributed s‐type Gaussian functions with positions and exponents optimized so as to support Hartree–Fock total energies with an accuracy approaching the sub‐μHartree level, Dirac–Hartree–Fock–Coulomb calculations are reported for the ground states of the H2, LiH, and BH molecules at their respective equilibrium geometries. The calculated energies are compared with those obtained by Kullie et al. using the finite element technique for the Dirac–Hartree–Fock–Coulomb problem. Finite basis set calculations using the Dirac–Hartree–Fock–Breit approximation are also reported and compared with a first‐order treatment of the frequency‐independent Breit interaction. © 2002 Wiley Periodicals, Inc. Int J Quantum Chem, 2002
Liquid chromatography/electrospray tandem mass spectrometric analysis of incurred ractopamine residues in livestock tissues
Authors: Churchwell Mona I. , Holder C. Lee , Little David , Preece Steve , Smith David J. , Doerge Daniel R.
Published: October 2002

Ractopamine HCl is a β‐adrenergic agonist (β‐agonist) recently approved by the U.S. Food and Drug Administration, but not other governmental agencies, for use in finishing swine. For these reasons, it was important to develop and validate mass spectrometric methods for the detection and confirmation of ractopamine residues in livestock marker tissues. Incurred tissues in cattle, sheep, turkeys, and ducks were generated during 7‐day ractopamine feeding (20 ppm in diets) periods. Disposition of ractopamine residues in liver and pigmented retinal epithelium was determined in animals slaughtered with withdrawal periods of 0, 3, and 7 days. Ractopamine residues, purified using solid‐phase extraction, were measured using liquid chromatography (LC) and electrospray with detection by tandem mass spectrometry (MS/MS) in the multiple reaction‐monitoring (MRM) mode. Total ractopamine residues (parent ractopamine + hydrolyzed conjugates) in liver were detected in all species on withdrawal day 0 (2–97 ppb) and were greatly diminished in all species by withdrawal day 7 (<1 ppb). Bovine and ovine retina had lower levels of ractopamine (0.5–3 ppb) than liver, and occular residues increased with withdrawal time, suggesting redistribution into this tissue. Lower limits of quantification were found to be approximately 0.1 ppb in liver and retina. Incurred ractopamine residues were confirmed by the precise and accurate agreement of MRM intensity ratios of diagnostic fragment ions (m/z 284, 164, and 121) from the protonated molecule between ractopamine residues in incurred samples and an authentic ractopamine standard. The limits of confirmation in liver and retina using recognized acceptance criteria were below 1 ppb. The high sensitivity and specificity for measurement and confirmation of ractopamine residues suggests this method will be applicable for regulatory residue surveillance programs. Copyright © 2002 John Wiley & Sons, Ltd.
Direct‐injection high performance liquid chromatography ion trap mass spectrometry for the quantitative determination of olanzapine, clozapine and N‐desmethylclozapine in human plasma
Authors: Kollroser Manfred , Schober Caroline
Published: October 2002

A specific and sensitive direct‐injection high performance liquid chromatography electrospray ionization tandem mass spectrometry (HPLC/ESI‐MS/MS) method has been developed for the rapid identification and quantitative determination of olanzapine, clozapine, and N‐desmethylclozapine in human plasma. After the addition of the internal standard dibenzepin and dilution with 0.1% formic acid, plasma samples were injected into the LC/MS/MS system. Proteins and other large biomolecules were removed during an online sample cleanup using an extraction column (1 × 50 mm i.d., 30 µm) with a 100% aqueous mobile phase at a flow rate of 4 mL/min. The extraction column was subsequently brought inline with the analytical column by automatic valve switching. Analytes were separated on a 5 µm Symmetry C18 (Waters) analytical column (3.0 × 150 mm) with a mobile phase of acetonitrile/0.1% formic acid (20:80, v/v) at a flow rate of 0.5 mL/min. The total analysis time was 6 min per sample. The inter‐ and intra‐assay coefficients of variation for all compounds were <11%. By eliminating the need for extensive sample preparation, the proposed method offers very large savings in total analysis time. Copyright © 2002 John Wiley & Sons, Ltd.
An original approach to determining traces of tetracycline antibiotics in milk and eggs by solid‐phase extraction and liquid chromatography/mass spectrometry
Authors: Bruno Federica , Curini Roberta , Corcia Antonio Di , Nazzari Manuela , Pallagrosi Marco
Published: October 2002

An original and highly specific method able to identify and quantify traces of five tetracycline antibiotics (TCAs) in milk and eggs is presented. This method uses a single solid‐phase extraction (SPE) cartridge for simultaneous extraction and purification of TCAs in the above matrices. After diluting 5 mL of intact whole milk or 2 g egg samples with Na2EDTA‐containing water, samples are passed through a 0.5‐g Carbograph 4 extraction cartridge. After analyte elution from the SPE cartridge, an aliquot of the final extract is injected into a liquid chromatography/mass spectrometry (LC/MS) instrument equipped with an electrospray ion source and a single quadrupole. MS data acquisition is performed in the positive‐ion mode and by a time‐scheduled multiple‐ion selected ion‐monitoring program. With methanol as organic modifier, the in‐source collision‐induced dissociation (CID) process generated fragment ions able to pick up one methanol molecule. In several cases, these methanol‐adduct fragment ions have m/z values higher than those of the protonated molecules. This event is rarely encountered in MS, thus making the analysis of TCAs by this method extremely specific. Compared with a conventional published method, the present protocol extracted larger amounts of TCAs from both milk and egg and decreased the analysis time by a factor of 3. Recovery of TCAs in milk at the 25‐ppb level ranged between 81 and 96% with relative standard deviation (RSD) no larger than 9%. Recovery of TCAs in egg at the 50‐ppb level ranged between 72 and 92% with RSD no larger than 7%. Estimated limits of quantification(S/N = 10) of the method were 2–9 ppb TCAs in whole milk and 2–19 ppb TCAs in eggs. Copyright© 2002 John Wiley & Sons, Ltd.
Rapid quantitation of globotriaosylceramide in human plasma and urine: a potential application for monitoring enzyme replacement therapy in Anderson‐Fabry disease
Authors: Boscaro Francesca , Pieraccini Giuseppe , Marca Giancarlo la , Bartolucci Gianluca , Luceri Cristina , Luceri Francesca , Moneti Gloriano
Published: October 2002

A method for measuring globotriaosylceramide (Gb3, or GL3) levels in plasma and urine of humans affected by Anderson‐Fabry disease has been developed. The analyses are performed using flow injection analysis‐electrospray ionization‐tandem mass spectrometry (FIA‐ESI‐MS/MS). The method is rapid, sensitive and hence suitable for high‐throughput analyses, requiring only a simple 50‐fold dilution for the preparation of plasma and urine samples. The detection of the analytes of interest was achieved using a triple quadrupole instrument operating in the multiple reaction monitoring mode. The linearity of the calibration standard responses, the intra‐ and inter‐assay precision, the accuracy and the detection limit of the method were evaluated. The proposed method allows a rapid and accurate assessment of globotriaosylceramide in biological samples. Data obtained from healthy volunteers and Anderson‐Fabry affected subjects suggest a potential role for this technique in monitoring the effectiveness of Anderson‐Fabry disease therapy. The results obtained in two actual cases treated with enzyme replacement therapy are reported and discussed. Copyright © 2002 John Wiley & Sons, Ltd.
A novel structural analysis of glycerophosphocholines as TFA/K+ adducts by electrospray ionization ion trap tandem mass spectrometry
Authors: Ho Yen‐Peng , Huang Ping‐Chen
Published: October 2002

When collisionally activated dissociation (CAD) of glycerophosphocholine (GPC) species is examined using quadrupole ion trap mass spectrometry (QITMS), the spectral patterns differ from those obtained using sector or quadrupole mass spectrometry. Methods employed in the structural analysis of GPCs using a sector or quadrupole mass spectrometers are not necessarily useful for an ion trap mass spectrometer. A novel method is presented for structurally analyzing GPCs that involves the CAD of trifluoroacetic acid (TFA) adducts of kaliated GPCs. Solutions of GPCs in 0.1% TFA/methanol were electrosprayed to produce precursor ions by attaching a trifluoroacetic acid (TFA) molecule to a kaliated GPC molecule. The CAD‐MS/MS spectra obtained by QITMS revealed a dramatic increase in the abundance of fragment ions, corresponding to the losses of sn‐1 and sn‐2 fatty acyl substituents. A preferential loss of the sn‐1 fatty acyl group over the loss of the sn‐2 fatty acyl group was observed among the GPC standards examined. A GPC extract from egg yolk was directly analyzed by this method without prior separation. The identities and positions of fatty acyl substituents of over 20 GPC species were identified. Some isomers present in very low relative abundance, which could not be analyzed by QITMS/MS using other ions as precursors, were identified by the TFA attachment method. Copyright © 2002 John Wiley & Sons, Ltd.
On the use of breakdown graphs combined with energy‐dependent mass spectrometry to provide a complete picture of fragmentation processes
Authors: Butcher Colin P. G. , Dyson Paul J. , Johnson Brian F. G. , Langridge‐Smith Patrick R. R. , McIndoe J. Scott , Whyte Christopher
Published: October 2002

Both breakdown graphs and energy‐dependent (ED) maps provide a means of visually representing the fragmentation processes resulting from collision‐induced dissociation at different energies. The two presentation methods may be combined for a complete picture of the appearance, disappearance and maximum abundance collision potentials of each of the ions involved in the fragmentation process. A demonstration of this approach is presented using two very different classes of compound, an amino acid and a transition metal carbonyl cluster. Copyright © 2002 John Wiley & Sons, Ltd.
Amino acid and peptide conjugates of protoporphyrin: preparation and analysis by high‐performance liquid chromatography, high‐performance liquid chromatography/electrospray ionization mass spectrometry and matrix‐assisted laser desorption/ionization time‐of‐flight mass spectrometry
Authors: Razzaque M. A. , Lord G. A. , Lim C. K.
Published: October 2002

Amino acid and peptide conjugates of protoporphyrin have been prepared by reacting protoporphyringen with cysteine, glutathione and peptides containing a free thiol group under acidic conditions. The conjugates were formed by the addition of the thioamino acids or peptides to the vinyl groups of protoporphyrin during the autoxidation of protoporphyinogen to protoporphyrin and is free‐radical‐mediated. The conjugates were separated by high‐performance liquid chromatography (HPLC) and characterized by HPLC/electrospray ionization mass spectrometry (HPLC/ESI‐MS) and matrix‐assisted laser desorption/ionization time‐of‐flight mass spectrometry (MALDI‐TOFMS). All the conjugates formed were diconjugates consisting of diastereoisomers. Copyright © 2002 John Wiley & Sons, Ltd.
Quantitative analysis of two‐dimensional gel‐separated proteins using isotopically marked alkylating agents and matrix‐assisted laser desorption/ionization mass spectrometry
Authors: Gehanne Sylvie , Cecconi Daniela , Carboni Lucia , Righetti Pier Giorgio , Domenici Enrico , Hamdan Mahmoud
Published: October 2002

We describe a simple approach for the relative quantification of individual proteins within a mixture. The method is based on the differential labelling of the mixtures by use of a commercially available acrylamide and deuterium‐labelled [2,3,3′‐d3]‐acrylamide to alkylate proteins prior to two‐dimensional (2‐D) gel electrophoresis. The tryptic digests of the separated proteins were subjected to reflector matrix‐assisted laser desorption/ionization time‐of‐flight (MALDI‐TOF) analysis and the relative peak heights of cysteine‐containing peptides were used to quantify their precursor proteins. This approach was tested for the relative quantification of proteins within an artificial mixture of standard proteins and for proteins observed in a 2‐D map of rat serum. A good correlation was found between the measured ratios derived from MALDI‐TOF data and those theoretically calculated prior to 2‐D analysis via known mixing ratios of the two alkylating reagents. The described procedure has proved to be effective for comparative measurements of protein abundances within the investigated mixtures. Copyright © 2002 John Wiley & Sons, Ltd.
On the covariance of the level sizes in random recursive trees
Authors: van der Hofstad Remco , Hooghiemstra Gerard , Van Mieghem Piet
Published: October 2002

In this paper we study the covariance structure of the number of nodes k and l steps away from the root in random recursive trees. We give an analytic expression valid for all k, l and tree sizes N. The fraction of nodes k steps away from the root is a random probability distribution in k. The expression for the covariances allows us to show that the total variation distance between this (random) probability distribution and its mean converges in probability to zero. © 2002 Wiley Periodicals, Inc. Random Struct. Alg., 20: 519–539, 2002
Large‐scale site diversity for satellite communication networks
Authors: Luglio M. , Mancini R. , Riva C. , Paraboni A. , Barbaliscia F.
Published: October 2002

The utilization of high frequencies, such as Ka‐band and beyond, necessary to avoid the highly congested lower satellite frequencies and to get larger bandwidth availability is considered for many developing satellite systems.

The new satellite low‐margin systems in Ka‐band will need to be designed using fade countermeasures to counteract rain attenuation. One of these techniques foresees the possibility of switching the communication link among different Earth stations spread on a very large territory to reduce the system outage time to the joint outage time of all the stations.

The design of such systems depends on the probability that the Earth stations simultaneously exceed their margins.

In this paper, a well‐assessed model is utilized for the prediction of joint statistics of rain attenuation in multiple locations, using Monte Carlo simulation. The model is based on a pair of multi‐variate normal processes whose parameters are related to those characterizing the single‐location statistics and whose covariance matrices are assumed to depend only on the distances between locations.

The main results concerning both the probability and margin improvement will be presented and discussed. Copyright © 2002 John Wiley & Sons, Ltd.
Interference evaluations and simulations for multisatellite multibeam systems
Authors: Loreti Pierpaolo , Luglio Michele
Published: October 2002

Third generation communication systems will be characterized by full integration between terrestrial and satellite components. To this aim, global coverage along with not severe requirements for user terminals are mandatory for the satellite segment and the use of constellations of satellites in low or medium Earth orbits (LEO or MEO) seems to be a viable solution. Those satellite systems will adopt multibeam antennas to achieve high spectral efficiency and low‐cost terminals. Thus, interference becomes one of the most limiting factors in terms of both link availability and capacity.

The paper presents a more complete interference model than previously published in literature. The identification of the interfering users set has been introduced and all the factors impacting interference generation or isolation have been considered in case of both FDMA and CDMA access. This model is suitable for instantaneous analysis of multisatellite constellations. It has been implemented and time‐domain simulations have been performed to evaluate the impairments due to co‐channel interference for different access techniques for LEO configuration.

Simulation results on interference and users spatial distribution, on trade‐offs between interference and system capacity will be presented. Finally, the main interference mitigation techniques will be listed and discussed. Copyright © 2002 John Wiley & Sons, Ltd.
Arguments, contradictions, resistances, and conceptual change in students' understanding of atomic structure
Authors: Niaz Mansoor , Aguilera Damarys , Maza Arelys , Liendo Gustavo
Published: October 2002

Most general chemistry courses and textbooks emphasize experimental details and lack a history and philosophy of science perspective. The objective of this study is to facilitate freshman general chemistry students' understanding of atomic structure based on the work of Thomson, Rutherford, and Bohr. It is hypothesized that classroom discussions based on arguments/counterarguments of the “heuristic principles,” on which these scientists based their atomic models, can facilitate students' conceptual understanding. This study is based on 160 freshman students enrolled in six sections of General Chemistry I (three sections formed part of the experimental group). All three models (Thomson, Rutherford, and Bohr) were presented to the experimental and control group students in the traditional manner, as found in most textbooks. After this, the three sections of the experimental group participated in the discussion of six items with alternative responses. Students were first asked to select a response and then participate in classroom discussions leading to arguments in favor or against the selected response and finally select a new response. Three weeks after having discussed the six items, both the experimental and control groups presented a monthly exam (based on the three models) and after another 3 weeks a semester exam. Results obtained show that given the opportunity to argue and discuss, students' understanding can go beyond the simple regurgitation of experimental details. Performance of the experimental group showed contradictions, resistances, and progressive conceptual change with considerable and consistent improvement in the last item. It is concluded that if we want our students to understand scientific progress and practice, then it is important that we include the experimental details not as a “rhetoric of conclusions” (Schwab, 1962, The teaching of science as enquiry, Cambridge, MA, Harward University Press; Schwab, 1974, Conflicting conceptions of curriculum, Berkeley, CA, McCutchan) but as “heuristic principles” (Lakatos, 1970, Criticism and the growth of knowledge, Cambridge, UK, Cambridge University Press, pp. 91–195), which were based on arguments, controversies, and interpretations of the scientists. © 2002 Wiley Periodicals, Inc. Sci Ed 86:505–525, 2002; Published online in Wiley Interscience (www.interscience.wiley.com). DOI 10.1002/sce.10035
Position and posture measurements and shape recognition of columnar objects using an ultrasonic sensor array and neural networks
Authors: Ohtani Kozo , Baba Mitsuru , Konishi Tadataka
Published: October 2002

A new method for measuring the position and posture (pose) and recognizing the shape using ultrasonic wave sound pressure signals and neural networks is proposed. In most of the past methods of this kind, the characteristic quantities have been based on either time of flight methods or acoustic holographic methods. In these methods, measuring and recognizing the width and depth directions simultaneously with a high resolution has been difficult in principle. In this paper, the problems of the past methods are resolved by changing the viewpoints by using criteria such as the peak values of the penetrating and reflecting waveforms, their positions, their deflection points, and their intervals when ultrasonic waves are directed onto a measured object, as characteristic quantities given to neural networks. In addition, a prototype measuring and recognizing system implementing the proposed scheme is constructed by introducing a circuit for detecting the peak positions of the sound pressure signal distribution waveforms with high resolution. The experimental results are satisfactory in position measurements and shape recognition, and confirm that the method is applicable to rectangular prisms and the like. It is shown that the position and pose measurements and shape recognition can be realized with high resolution in both the width and depth directions by this scheme, and that the proposed method is very effective when applied to position and pose measurements and shape recognition and the like ultrasonically. © 2002 Wiley Periodicals, Inc. Syst Comp Jpn, 33(11): 27–38, 2002; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/scj.10103
Auditory scene analysis based on time‐frequency integration of shared FM and AM (I): Lagrange differential features and frequency‐axis integration
Authors: Abe Mototsugu , Ando Shigeru
Published: October 2002

We will propose in this paper a new algorithm for a computational implementation of auditory scene analysis. This algorithm forms a three‐layer structure of (1) subband decomposition by wavelet transform, (2) characterization of subband signal fragments by instantaneous frequency, frequency change rate, and amplitude change rate, and (3) frequency integration of subband signal features by voting method. We will perform the grouping and integration by voting the subband signal fragments into a nonparametric multipeak probability density distribution expressing “possibility of streams”; and then the recognition of the streams and the extraction of the stream parameters are realized by tracing its greatest point. It is confirmed from basic experiments for synthesized sounds and voices that the fundamental frequency/frequency change rate/amplitude change rate can be separated and estimated from multiple streams. © 2002 Wiley Periodicals, Inc. Syst Comp Jpn, 33(11): 95–106, 2002; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/scj.1167
Quantitative analysis of conductive coatings by radiofrequency‐powered glow discharge optical emission spectrometry: hydrogen, d.c. bias voltage and density corrections
Authors: Payling Richard , Michler Johann , Aeberhard Max
Published: October 2002

Radiofrequency‐powered glow discharge optical emission spectrometry (rf‐GDOES) can provide rapid quantitative depth profiles of both conductive and non‐conductive coatings. Examples of three types of conductive coatings are shown here: galvanized steel, a TiN hard coating and two electrical coatings. Expected compositions and thicknesses were achieved when both d.c. bias voltage and hydrogen corrections were applied. A new algorithm for calculating the density of mixed metals, oxides and nitrides is presented. The hydrogen correction is also applied to the extreme surface of a metal coating for the first time. Copyright © 2002 John Wiley & Sons, Ltd.
Dissolution of UV‐cured polymeric films: a fluorescence study
Authors: Uǧur Şaziye , Akkök Beril , Pekcan Önder
Published: October 2002

A steady‐state fluorescence (SSF) technique was used for studying the dissolution of UV‐cured polymer films. These films are formed from poly(methyl methacrylate) (PMMA) chains labelled with pyrene, which was introduced as a fluorescence probe to monitor the dissolution processes. The PMMA films of various ethylene glycol dimethacrylate (EGDM) contents, cured by ultraviolet (UV) radiation, were dissolved in chloroform–heptane (20 : 80, v/v) mixtures. Dissolution of the films was monitored in real‐time by the change in pyrene fluorescence intensity, IP, in the solvent mixture. It was observed that the maximum pyrene intensity, IP∞, increased above a critical EGDM content, which was attributed to the formation of a percolation cluster, i.e. UV‐cured films hardly dissolve above this critical EGDM content in the film. Desorption rates, Dd, were measured for films prepared with various EGDM contents. Copyright © 2002 John Wiley & Sons, Ltd.
Soft x‐ray absorption spectroscopy study of oxide layers on titanium alloys
Authors: López M. F. , Soriano L. , Palomares F. J. , Sánchez‐Agudo M. , Fuentes G. G. , Gutiérrez A. , Jiménez J. A.
Published: October 2002

Soft x‐ray absorption spectroscopy (XAS) has been used to perform chemical analysis of oxide films formed after contact with air, both at room temperature and at 750° C, on three titanium alloys. The alloys investigated were Ti–13Nb–13Zr, Ti–15Zr–4Nb and Ti–7Nb–6Al. Soft x‐ray absorption spectra were taken at the Ti 2p and O 1s edges. The spectra corresponding to the room‐temperature‐oxidized samples are similar for the three alloys and show the presence of native oxide with a small metallic contribution. For the heat‐treated samples, the alloying elements as well as element diffusion play a significant role in the formation of the oxide layer. In this case, the spectra exhibit clear differences between the TiNbZr alloys and Ti–7Nb–6Al. The oxide layer of the two TiNbZr alloys for the different heat treatment times is composed of TiO2 in the form of rutile. However, for Ti–7Nb–6Al short heat treatments give rise to the formation of Al2TiO5. By increasing the oxidation time, an Al2O3 layer grows on the initial oxide film, becoming thicker as the exposure time is enhanced. Copyright © 2002 John Wiley & Sons, Ltd.
Fixed‐effect versus random‐effect models for evaluating therapeutic preferences
Authors: Lee Y.
Published: October 2002

A preference trial is a special form of cross‐over trial where clinical conditions determine when patients change treatment, in a prescribed order. This leads to binary responses with variable lengths. In cross‐over trials with normal responses, patient effect may be treated as either fixed or random. However, with binary responses, random‐ and fixed‐effect assumptions may lead to very different conclusions, so that one is no longer an alternative to the other. Copyright © 2002 John Wiley & Sons, Ltd.
Reproducibility probability in clinical trials
Authors: Shao Jun , Chow Shein‐Chung
Published: October 2002

For marketing approval of a new drug product, the United States Food and Drug Administration (FDA) requires that substantial evidence of the effectiveness of the drug product be provided through the conduct of at least two adequate and well‐controlled clinical trials. The purpose of conducting the second clinical trial is to study whether the clinical result from the first trial is reproducible in the second trial with the same study protocol. Under certain circumstance, the FDA Modernization Act of 1997 includes a provision to allow data from one adequate and well‐controlled clinical trial investigation and confirmatory evidence to establish effectiveness for risk/benefit assessment of drug and biological candidates for approval. In this paper, we introduce the concept of reproducibility probability for a given clinical trial, which is useful in providing important information for regulatory agencies in deciding whether a single clinical trial is sufficient and for pharmaceutical companies in adjusting the sample size in a future clinical trial. Three approaches, the estimated power approach, the method of confidence bounds and the Bayesian approach, are studied in evaluating reproducibility probabilities under several study designs commonly used in clinical trials. Copyright © 2002 John Wiley & Sons, Ltd.
Extended shifts in ambulance work: influences on health
Authors: Pisarski Anne , Bohle Philip , Callan Victor J.
Published: October 2002

Shiftwork is a major source of stress for many workers. This study highlights the role that organizational and psychosocial variables play in alleviating the negative health effects of 10‐ and 14‐h shifts. It examines the direct and mediated effects of coping strategies, social support and control of shifts on work/non‐work conflict and subjective health. Participants are 60 ambulance workers, aged 22 to 55 years. A structural equation model with good fit demonstrates complex effects of social support from various sources (supervisors, co‐workers and family), coping and control on work/non‐work conflict and subjective health. Conceptually, the research contributes to the development of a theoretical framework that can assist in explaining how key psychosocial and organizational variables influence the psychological and physical symptoms experienced by shiftworkers. Copyright © 2002 John Wiley & Sons, Ltd.
Embryotoxicity of the pesticide mirex in vitro
Authors: El‐Bayomy Ahmed A. , Smoak Ida W. , Branch Stacy
Published: October 2002

Mirex is a pesticide that is environmentally stable, accumulates in body tissues, and is embryo‐ and feto‐toxic at high concentrations in vivo. This study is the first to evaluate the effects of mirex on organogenesis‐stage embryos in vitro. Mouse embryos were exposed on gestation day 8.5 for 24 h in whole‐embryo culture to mirex at 100, 200, or 400 µg/ml dissolved in xylene and compared with xylene‐treated controls (1, 2, or 4 µl/ml, respectively) and untreated controls. Embryos were evaluated for malformations, somite number, total protein content, and visceral yolk sac circulation. Potential embryotoxic mechanisms were evaluated by using PCNA stain for cell proliferation and the TUNEL assay for apoptotic cell death. Mirex‐exposed embryos demonstrated increased malformation rates and decreased total embryonic protein contents at ≥200 µg/ml mirex, and decreased somite numbers and VYS circulation at ≥100 µg/ml mirex, compared with xylene‐treated controls. There was no difference in PCNA levels or TUNEL staining in mirex‐treated embryos compared with xylene‐treated controls or untreated controls. Thus, mirex is embryotoxic in vitro to early organogenesis stage mouse embryos at concentrations ≥100 µg/ml, but the effects do not appear to be mediated by changes in cell proliferation or apoptotic cell death. © 2002 Wiley‐Liss, Inc.
Overview of results from the WaterTox intercalibration and environmental testing phase II program: Part 1, statistical analysis of blind sample testing
Authors: Ronco A. , Gagnon P. , Diaz‐Baez M. C. , Arkhipchuk V. , Castillo G. , Castillo L. E. , Dutka B. J. , Pica‐Granados Y. , Ridal J. , Srivastava R. C. , Sánchez A.
Published: October 2002

There is an urgent need to evaluate the presence of toxicants in waters used for human consumption and to develop strategies to reduce and prevent their contamination. The International Development Research Centre undertook an intercalibration project to develop and validate a battery of bioassays for toxicity testing of water samples. The project was carried out in two phases by research institutions from eight countries that formed the WaterTox network. Results for the first phase were reported in the special September 2000 issue of Environmental Toxicology. Phase II involved toxicity screening tests of environmental and blind samples (chemical solutions of unknown composition to participating laboratories) using the following battery: Daphnia magna, Hydra attenuata, seed root inhibition with Lactuca sativa, and Selenastrum capricornutum. This battery was also used to assess potential toxicity in concentrated (10×) water samples. Results are presented for a set of six blind samples sent to the participating laboratories over a 1‐year period. Analyses were performed for each bioassay to evaluate variations among laboratories of responses to negative controls, violations of test quality control criteria, false positive responses induced by sample concentration, and variability within and between labs of responses to toxic samples. Analyses of the data from all bioassays and labs provided comparisons of false positive rates (based on blind negative samples), test sensitivities to a metal or organic toxicant, and interlaboratory test variability. Results indicate that the battery was reliable in detecting toxicity when present. However, some false positives were identified with a concentrated soft‐water sample and with the Lactuca and Hydra (sublethal end‐point) tests. Probabilities of detecting false positives for individual and combined toxic responses of the four bioassays are presented. Overall, interlaboratory comparisons indicate a good reliability of the battery. © 2002 Wiley Periodicals, Inc. Environ Toxicol 17: 232–240, 2002; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/tox.10047
Overview of results from the WaterTox intercalibration and environmental testing phase II program: Part 2, ecotoxicological evaluation of drinking water supplies
Authors: Diaz‐Baez M.C. , Sánchez W.A. , Dutka B.J. , Ronco A. , Castillo G. , Pica‐Granados Y. , Castillo L.E. , Ridal J. , Arkhipchuk V. , Srivastava R.C.
Published: October 2002

Because of rapid population growth, industrial development, and intensified agricultural production increasing amounts of chemicals are being released into the environment, polluting receiving water bodies around the world. Given the potential health risk associated with the presence of toxicants in water sources used for drinking yet the scarcity of available data, there is a need to evaluate these waters and develop strategies to reduce and prevent their contamination. The present study examined the applicability of a battery of simple, inexpensive bioassays in environmental management and the relevance of the test results in establishing the toxicological quality of water sources and drinking water within the framework of the eight‐country WaterTox Network, sponsored by the International Development Research Centre, Ottawa, Canada. Seventy‐six samples were collected from surface and groundwater sources and seven samples from drinking water treatment plants. Each sample was tested with a core battery of bioassays (Daphnia magna, Hydra attenuata, and Lactuca sativa root inhibition tests) and a limited set of physical and chemical parameters. In addition, three labs included the Selenastrum capricornutum test. When no toxic effects were found with the battery, samples were concentrated 10× using a solid‐phase extraction (SPE) procedure. Nonconcentrated natural water samples produced a toxic response in 24% of cases with all three core bioassays. When all bioassays are considered, the percentage of raw samples showing toxicity with at least one bioassay increased to 60%. Of seven treated drinkingwater samples, four showed toxicity with at least one bioassay, raising the possibility that treatment processes in these instances were unable to remove toxic contaminants. The Daphnia magna and Hydra attenuata tests indicated a high level of sensitivity overall. Although only three of the eight countries used S. capricornutum, it proved to be an efficient and reliable bioassay for toxicity assessment. © 2002 Wiley Periodicals, Inc. Environ Toxicol 17: 241–249, 2002; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/tox.10052