bluuebunny/crossref_metadata_2025 huggingface dataset:
The effect of correlated exponential service times on single server tandem queues
Authors: Mitchell C. R. , Paulson A. S. , Beswick C. A.
Published: May 2007

An investigation via simulation of system performance of two stage queues in series (single server, first‐come, first‐served) under the assumption of correlated exponential service times indicates that the system's behavior is quite sensitive to departures from the traditional assumption of mutually independent service times, especially at higher utilizations. That service times at the various stages of a tandem queueing system for a given customer should be correlated is intuitively appealing and apparently not at all atypical. Since tandem queues occur frequently, e.g. production lines and the logistics therewith associated, it is incumbent on both the practitioner and the theoretician that they be aware of the marked effects that may be induced by correlated service times. For the case of infinite interstage storage, system performance is improved by positive correlation and impaired by negative correlation. This change in system performance is reversed however for zero interstage storage and depends on the value of the utilization rate for the case where interstage storage equals unity. The effect due to correlation is shown to be statistically significant using spectral analytic techniques. For correlation equal unity and infinite interstage storage, results are provided for two through twenty‐five stages in series to suggest how adding stages affects system performance for ρ>0. In this extreme case of correlation, adding stages has an effect on system performance which depends markedly on the utilization rate. Recursive formulae for the waiting time per customer for the cases of zero, one, and infinite interstage storage are derived.
Single‐lane bridge serving two‐lane traffic
Authors: Eshcoli Z. , Adiri I.
Published: May 2007

This paper presents a mathematical model of a single‐lane bridge serving two‐way traffic in alternating directions (with an FIFO rule observed within each directional queue). While the bridge serves cars moving in one direction, cars approaching from the opposite direction wait in a queue at its foot. When cars in the current direction finish crossing the bridge, it begins serving cars from the other direction, if any are present. A newly‐arrived car finding an empty bridge mounts it immediately. Several cars moving in the same direction may occupy the bridge simultaneously. The crossing speed is assumed to be constant, and the arrival processes in both directions are assumed to be independent, homogeneous Poisson processes. A generalization of the alternating‐priority models [1, 2] is developed to arrive at the Laplace‐Stieltjes transform and the expected value of the flow time (the time interval between the moments of arrival at the bridge and departure from it) for steady state conditions. The results are discussed and some examples are presented graphically.
Optimal control for multi‐servers queueing systems under periodic review
Authors: Huang C. C. , Brumelle S. L. , Sawaki K. , Vertinsky I.
Published: May 2007

This paper deals with the problem of finding the optimal dynamic operating policy for an M/M/S queue. The system is observed periodically, and at the beginning of each period the system controller selects the number of service units to be kept open during that period. The optimality criterion used is the total discounted cost over a finite horizon.
A convex property of an ordered flow shop sequencing problem
Authors: Panwalkar S. S. , Khan A. W.
Published: May 2007

A flow shop sequencing problem with ordered processing time matrices is considered. A convex property for the makespan sequences of such problems is discussed. On the basis of this property an efficient optimizing algorithm is presented. Although the proof of optimality has not been developed, several hundred problems were solved optimally with this procedure.
A manpower planning/capital budgeting model (MAPCAB)
Authors: Clark Rolf H. , Comerford Robert A.
Published: May 2007

A deterministic resource allocation model is developed to optimize defense effectiveness subject to budget, manpower, and risk constraints. The model consists of two major submodels connected by a heuristic. The first is a mathematical program which optimizes the multiperiod weapon mix subject to the constraint set. The second is a manpower supply model based on a transition matrix in which individual transitions are functions of personnel related budgets and historical transition rates. The heuristic marries the submodels through an iterative process leading to improved solutions. An example is provided which demonstrates how systems are undercosted and overprocured if manpower supply is not properly reflected relative to manpower demand.
An F approximation for two‐parameter weibull and log‐normal tolerance bounds based on possibly censored data
Authors: Mann Nancy R.
Published: May 2007

An approximation suggested in Mann, Schafer and Singpurwalla [18] for obtaining small‐sample tolerance bounds based on possibly censored two‐parameter Weibull and lognormal samples is investigated. The tolerance bounds obtained are those that effectively make most efficient use of sample data. Values based on the approximation are compared with some available exact values and shown to be in surprisingly good agreement, even in certain cases in which sample sizes are very small or censoring is extensive. Ranges over which error in the approximation is less than about 1 or 2 percent are determined. The investigation of the precision of the approximation extends results of Lawless [8], who considered large‐sample maximum‐likelihood estimates of parameters as the basis for approximate 95 percent Weibull tolerance bounds obtained by the general approach described in [18]. For Weibull (or extreme‐value) data the approximation is particularly useful when sample sizes are moderately large (more than 25), but not large enough (well over 100 for severely censored data) for asymptotic normality of estimators to apply. For such cases simplified efficient linear estimates or maximum‐likelihood estimates may be used to obtain the approximate tolerance bounds. For lognormal censored data, best linear unbiased estimates may be used, or any efficient unbiased estimators for which variances and covariances are known as functions of the square of the distribution variance.
An M/M/1 queue with delayed feedback
Authors: Hannibalsson Ingjaldur , Disney Ralph L.
Published: May 2007

We present some results for M/M/1 queues with finite capacities with delayed feedback. The delay in the feedback to an M/M/1 queue is modelled as another M‐server queue with a finite capacity. The steady state probabilities for the two dimensional Markov process {N(t), M(t)} are solved when N(t) = queue length at server 1 at t and M(t) = queue length at server 2 at t. It is shown that a matrix operation can be performed to obtain the steady state probabilities. The eigenvalues of the operator and its eigenvectors are found. The problem is solved by fitting boundary conditions to the general solution and by normalizing. A sample problem is run to show that the solution methods can be programmed and meaningful results obtained numerically.
Solving multicommodity transportation problems using a primal partitioning simplex technique
Authors: Kennington Jeff L.
Published: May 2007

This paper presents the details for applying and specializing the work of Saigal [28] and Hartman and Lasdon [16] to develop a primal partitioning code for the multicommodity transportation problem. The emphasis of the paper is in presenting efficient data structure techniques for exploiting the underlying network structure of this class of problems. Computational experience with test problems whose corresponding linear programming formulation has over 400 rows and 2,000 columns is presented.
Stochastic transportation problems and other newtork related convex problems
Authors: Cooper Leon , Leblanc Larry J.
Published: May 2007

A class of convex programming problems with network type constraints is addressed and an algorithm for obtaining the optimal solution is described. The stochastic transportation problem (minimize shipping costs plus expected holding and shortage costs at demand points subject to limitations on supply) is shown to be amenable to the solution technique presented. Network problems whose objective function is non‐separable and network problems with side constraints are also shown to be solvable by the algorithm. Several large stochastic transportation problems with up to 15,000 variables and non‐negativity constraints and 50 supply constraints are solved.
A note on the strategy of restriction and degenerate linear programming problems
Authors: Holloway Charles A.
Published: May 2007

Using the general computational strategy of restriction, necessary conditions for optimality provide an alternative criterion for entering variables when degeneracies arises in linear programming problems. Although cycling may still occur, it is shown that if it is possible to make progress at the next iteration, the criterion is guaranteed to identify a non‐basic variable which increases the value of the basic solution, thereby reducing stalling. An alternative method for determining variables to exit the basis when degeneracies occur is also suggested.
Sequential tests for hypotheses concerning the product of poisson parameters with applications to problems in reliability and biometry
Authors: Harris B. , Soms A. P.
Published: May 2007

Sequential tests for the product of Poisson parameters based on the generalized incomplete modified Bessel (g.i.m.B.) distributions are given. Applications to reliability and biometry are indicated.
Relation between continuous and discrete time markovian decision problems
Authors: Kakumanu Prasadarao
Published: May 2007

An associated discrete (continuous) time Markovian decision problem for any given continuous (discrete) time Markovian decision model is formulated. A relationship between the continuous and associated discrete time discounted returns is obtained. This result is used to show the existence of a deterministic stationary policy that optimizes both discounted return functions. It is also proved that the same policy optimizes the average expected return for both continuous and the associated discrete time processes. The results obtained in this paper can be used to solve the continuous time Markovian decision problem by using the discrete time algorithms or vice versa.
Queueing models for spares provisioning
Authors: Gross Donald , Kahn Henry D. , Marsh Joseph D.
Published: May 2007

A population of items which break down at random times and require repair is studied (the classic “machine repair problem with spares”). It is desired to determine the number of repair channels and spares required over a multiyear planning horizon in which population size and component reliability varies, and a service level constraint is imposed. When an item fails, a spare (if available) is immediately dispatched to replace the failed item. The failed item is removed, transported to the repair depot, repaired, and then placed in the spares pool (which is constrained to be empty not more than 10% of the time) unless there is a backlog of requests for spares, in which case it is dispatched immediately. The first model considered treats removal, transportation, and repair as one service operation. The second model is a series queue which allows for the separate treatment of removal, transportation, and repair. Breakdowns are assumed Poisson and repair times exponential.
Optimal investment, pricing and replacement of computer resources
Authors: Kriebel Charles H. , Atkinson Anthony A. , Zia Huntley W. H.
Published: May 2007

The problem of multiple‐resource capacity planning under an infinite time horizon is analyzed using a nonlinear programming model. The analysis generalizes to the long term the short‐run pricing model for computer networks developed in Kriebel and Mikhail [5]. The environment assumes heterogeneous resource capacities by age (vingate), which service a heterogeneous and relatively captive market of users with known demand functions in each time period. Total variable operating costs are given by a continuous psuedoconcave function of system load, capacity, and resource age. Optimal investment, pricing, and replacement decision rules are derived in the presence of economies of scale and exogenous technological progress. Myopic properties of the decision rules which define natural (finite) planning subhorizons are discussed.
The one‐period, N‐location distribution problem
Authors: Karmarkar Uday S. , Patel Nitin R.
Published: May 2007

This paper studies the one‐period, general network distribution problem with linear costs. The approach is to decompose the problem into a transportation problem that represents a stocking decision, and into decoupled newsboy problems that represent the realization of demand with the usual associated holding and shortage costs. This approach leads to a characterization of optimal policies in terms of the dual of the transportation problem. This method is not directly suitable for the solution for large problems, but the exact solution for small problems can be obtained. For the numerical solutions of large problems, the problem has been formulated as a linear program with column generation. This latter approach is quite robust in the sense that it is easily extended to incorporate capacity constraints and the multiproduct case.
Monotone failure rates for multivariate distributions
Authors: Block Henry W.
Published: May 2007

It is shown that the monotone multivariate failure rates of Brindley and Thompson have no natural analog involving the multivariate failure rate function of Basu for absolutely continuous distributions. Quantities related to the multivariate failure rate function are used to define monotone failure rates. It is shown that these are equivalent to the monotone failure rates of Brindley and Thompson. Based on these quantities, the loss of memory property of Marshall and Olkin is characterized.
Confidence intervals in discrete event simulation: A comparison of replication and batch means
Authors: Law Averill M.
Published: May 2007

Suppose that we have enough computer time to make n observations of a stochastic process by means of simulation and would like to construct a confidence interval for the steady‐state mean. We can make k independent runs of m observations each (n=k.m) or, alternatively, one run of n observations which we then divide into k batches of length m. These methods are known as replication and batch means, respectively. In this paper, using the probability of coverage and the half length of a confidence interval as criteria for comparison, we empirically show that batch means is superior to replication, but that neither method works well if n is too small. We also show that if m is chosen too small for replication, then the coverage may decrease dramatically as the total sample size n is increased.
A note on the sum of a linear and linear‐fractional function
Authors: Schaible Siegfried
Published: May 2007

The sum of a linear and linear‐fractional function is investigated in terms of quasi‐convexity and quasi‐concavity. From this we obtain some insight into the nature of local optima of these functions useful in algorithms.
The simplex method for integral multicommodity networks
Authors: Evans James R.
Published: May 2007

The simplex method is interpreted as a labeling procedure for certain classes of multicommodity flow problems in a manner similar to that for single commodity networks. As opposed to general multicommodity algorithms, no explicit matrix inversion is required; all simplex operations are performed graph‐theoretically.
The search for an intelligent evader: Strategies for searcher and evader in the two‐region problem
Authors: Roberts D. M. , Gittins J. C.
Published: May 2007

This paper considers the search for an evader concealed in one of two regions, each of which is characterized by its detection probability. The single‐sided problem, in which the searcher is told the probability of the evader being located in a particular region, has been examined previously. We shall be concerned with the double‐sided problem in which the evader chooses this probability secretly, although he may not subsequently move: his optimal strategy consists of that probability distribution which maximizes the expected time to detection, while the searcher's optimal strategy is the sequence of searches which limits the evader to this expected time. It transpires for this problem that optimal strategies for both searcher and evader may generally be obtained to a surprisingly good degree of approximation by using the optimal strategies for the closely related (but far more easily solved) problem in which the evader is completely free to move between searches.
Determining confidence bounds for highly reliable coherent systems based on a paucity of component failures
Authors: Myhre Janet M. , Rosenfeld Andrew M. , Saunders Sam C.
Published: May 2007

A computationally simple method for obtaining confidence bounds for highly reliable coherent systems, based on component tests which experience few or no failures, is given. Binomial and Type I censored exponential failure data are considered. Here unknown component unreliabilities are ordered by weighting factors, which are firstly presumed known then sensitivity of the confidence bounds to these assumed weights is examined and shown to be low.
Approximations to the reliability of phased missions
Authors: Ziehms Harald
Published: May 2007

A system whose configuration (block diagram or fault tree) changes during consecutive time periods (phases) performs a “phased mission.” Recently, Esary and Ziehms have shown that any multiphase mission can be transformed into an equivalent, synthetic, single‐phase system, and thus that the phased mission problem can in principle be solved by standard reliability methods. We employ these ideas here to study approximations to mission reliability and to develop an algorithm which may be of practical interest. In addition, we extend the reliability calculus of Rubinstein, and Esary and Hayne, based on an approximate hazard transform, to phased missions, and we show how this extended calculus can be used in situations where phases are not of known fixed duration.
Inspection policies for deteriorating equipment characterized by n quality levels
Authors: Kander Z.
Published: May 2007

Inspection models deal with operating systems whose stochastic failure is detected by observations carried out intermittently. The current communication deals with systems in which N + 1 levels of quality can be diagnosed. Optimal policies leading to minimal loss are developed, while the system's distribution is represented by an (N + 1)‐state semi‐markov process. Based on previous studies of the authors, relative efficiencies of the proposed checking policies are ascertained, by comparison with the loss sustained if discrimination of quality by intermediate levels is disregarded and by viewing the system as one which is either good or failed. Various models are treated where checking, truncated checking, and monitoring policies optimize loss per cycle, per unit of time and per unit of good time. Numerical examples are given.
The error in the normal approximation to the multinomial with an increasing number of classes
Authors: Weiss Lionel
Published: May 2007

In an earlier paper, it was shown that under certain conditions, if the number of classes in a multinomial distribution increases as the number of trials increases, the probabilities assigned to arbitrary regions by the multinomial distribution are close to the probabilities assigned by the distribution of slightly rounded‐off normal random variables. A different method of studying the approximation of the multinomial distribution by a normal distribution is to use the multivariate Berry‐Esseen bound. In this paper, these two methods are compared, particularly with respect to the class of multinomial distributions for which the bounds on the error remain useful.
A probability model for initial crack size and fatigue life of gun barrels
Authors: Proschan F. , Sethuraman J.
Published: May 2007

With constant firing, metal fatigue produces cracks in a gun barrel. The useful life of the barrel comes to an end when a crack develops to a critical size. The theory of Fracture Mechanics suggests a formula for crack size growth rate. This formula can be used to determine the life of a barrel, depending on the initial and critical crack sizes and other factors. The initial crack size turns out to be a dominant factor. Unfortunately, accurate measurements are not generally available on the initial crack size. In this paper, we propose a simple probability model for the initial crack size and this, in turn, leads to a probability distribution of the life of the barrel. This last distribution is the well‐known exponential distribution with a location shift. The simplicity of this final result is one of the factors that make the model appealing.
A heuristic network procedure for the assembly line balancing problem
Authors: Pinto Peter A. , Dannenbring David G. , Khumawala Basheer M.
Published: May 2007

Proposed is a Heuristic Network (HN) Procedure for balancing assembly lines. The procedure uses simple heuristic rules to generate a network which is then traversed using a shortest route algorithm to obtain a heuristic solution. The advantages of the HN Procedure are: a) it generally yields better solutions than those obtained by application of the heuristics, and b) sensitivity analysis with different values of cycle time is possible without having to regenerate the network. The rationale for its effectiveness and its application to problems with paralleling are presented. Computational experience with the procedure on up to 50 task test problems is provided.
A targeting model that minimizes collateral damage
Authors: Grotte Jeffrey H.
Published: May 2007

This paper considers the problem of allocating weapons to achieve targeting objectives while simultaneously minimizing aggregate damage to surrounding nonmilitary facilities, each of which has an upper limit to the damage it is permitted to incur. A model is formulated which assumes only that damage to individual targets or associated facilities does not decrease as the number of allocated weapons increases. An implicit enumeration algorithm, based on that of Lawler and Bell is described that yields optimal integer solutions. An example is presented.
On the manipulation of transfer prices in a static environment
Authors: Bonin John P.
Published: May 2007

In a static environment, J. Hirschleifer's marginal cost solution to the transfer pricing problem is commonly accepted as analytically correct. However, actual pricing practice within Western corporations and socialist‐planned economies generally deviates from marginal cost pricing. Some form of average cost pricing is more commonly chosen. Recently in this journal, H. Enzer has claimed to show that some form of average cost pricing is indeed the analytically correct solution to the transfer pricing problem when choice of technique and manipulation are allowed. Enzer claims that optimal decisions made by each of two divisions according to their individual self‐interests are made compatible with overall firm optimization when the transfer price assigned to the internally‐transferred commodity is any form of average cost.

We show that the marginal cost solution is correct for Enzer's problem in the absence of manipulation by either division. Indeed, this was all that Hirschleifer claimed. In the process, we uncover a fundamental mathematical error in Enzer's argument. When manipulation of the transfer price by divisions is allowed, we demonstrate the faults with Enzer's average cost solution and conclude Hirschleifer's original statements on manipulation to be correct even in Enzer's environment. A final section briefly indicates the importance to the transfer pricing problem of a growing body of economic literature on incentive structures.
A note concerning asymmetric games on graphs
Authors: Roth Alvin E.
Published: May 2007

We consider a class of asymmetric two‐person games played on graphs, and characterize all the positions in the game.
A note on eoq under fund constraints
Authors: Kaplan Alan J.
Published: May 2007

An algorithm is developed to modify the Wilson Q to account for a short‐term expenditure constraint over a catalog of items. Representative results are shown and generalizations made.
Techniques for establishing ergodic and recurrence properties of continuous‐valued markov chains
Authors: Laslett G. M. , Pollard D. B. , Tweedie R. L.
Published: May 2007

We present techniques for classifying Markov chains with a continuous state space as either ergodic or recurrent. These methods are analogous to those of Foster for countable space chains. The theory is presented in the first half of the paper, while the second half consists of examples illustrating these techniques. The technique for proving ergodicity involves, in practice, three steps: showing that the chain is irreducible in a suitable sense; verifying that the mean hitting times on certain (usually bounded) sets are bounded, by using a “mean drift” criterion analogous to that of Foster; and finally, checking that the chain is such that bounded mean hitting times for these sets does actually imply ergodicity.

The examples comprise a number of known and new results: using our techniques we investigate random walks, queues with waiting‐time‐dependent service times, dams with general and random‐release rules, the s‐S inventory model, and feedback models.
User satisfaction, community participation and quality of life among Chinese wheelchair users with spinal cord injury: a preliminary study
Authors: Chan Sam C , Chan Alice P
Published: May 2007

The purpose of the present study was to investigate the relationships between spinal cord injury (SCI), wheelchair users' satisfaction, perceptions of their community participation and quality of life (QoL).Thirty‐one community wheelchair users with SCI were administered the Chinese version of the Quebec User Evaluation of Satisfaction with assistive Technology (C‐QUEST), the abbreviated Hong Kong version of the World Health Organization Quality of Life Questionnaire (WHO QoL‐BREF (HK)) and selected items of ‘Participation Restrictions’ and ‘Environmental Factors’ of the International Classification of Functioning Disability and Health (ICF). Only a weak correlation was found between the C‐QUEST services sub‐scores and one ICF environmental factor, that is, health‐related professionals (Spearman's r = 0.453; p < 0.05). The C‐QUEST device sub‐scores were also weakly correlated with four domain scores of the WHO QoL‐BREF (HK) (Spearman's r = 0.412–0.567; p < 0.05). Social relationship, participation in leisure and driving activities had a moderate association with scores of the WHO QoL‐BREF (HK) (−0.405 > Spearman's r > −0.583; p < 0.05). It is concluded that community participation (e.g. use of transportation) and human environment (e.g. friends and peers) were more related to QoL, than to users' satisfaction with a wheelchair. Further research with a larger sample is recommended to examine the variables related to SCI and QoL. Copyright © 2007 John Wiley & Sons, Ltd.
Synthesis and characterization of painted epoxy nanocomposites
Authors: Chang Ming‐Jen , Chang Lin‐Fen , Jiang George J.
Published: May 2007

Epoxy/SWN nanocomposites, based on the diglycidyl ether of bisphenol A (Epon 828) cured by polyoxypropylene triamine (T‐430), were prepared by in situ polymerization. The effect of SWN content on the nanocomposites was investigated, and the morphology and properties were elucidated. The degree of dispersion of SWN loading in the nanocomposites was demonstrated by using X‐ray diffraction and transmission electron microscope. The thermal and mechanical properties of the composite tended to become better, as the SWN content increased. Furthermore, we will also discuss the barrier properties and chemical resistance of the epoxy/SWN nanocomposites observed by scanning electron microscope. POLYM. COMPOS., 28:392–396, 2007. © 2007 Society of Plastics Engineers
Study on superabsorbent composite. XI. Effect of thermal treatment and acid activation of attapulgite on water absorbency of poly(acrylic acid)/attapulgite superabsorbent composite
Authors: Wang Wenji , Li An , Zhang Junping , Wang Aiqin
Published: May 2007

The effect of acid activation and thermal treatment of attapulgite on water absorbency of superabsorbent composite were investigated. Under the same preparation conditions, superabsorbent composite prepared with natural attapulgite exhibited a water absorbency of 639 g/g and it merely kept 71% of its initial water absorbency after 5 times of swelling–deswelling–reswelling test. However, superabsorbent composites prepared with 2–10 M hydrochloric acid acidified attapulgite and 100–400°C thermal treated attapulgite respectively exhibited the water absorbency of 884–1,241 g/g and 701–1,515 g/g. Also, those superabsorbent composites can keep 87% and 85% of their initial water absorbency after 5 times of swelling–deswelling–reswelling test, respectively. These results showed that, compared with superabsorbent composite prepared with natural attapulgite, the comprehensive water‐absorbing properties of poly(acrylic acid)/ attapulgite superabsorbent composites were improved effectively by acid activation and thermal treatment of attapulgite. This improvement of water absorbencies and gel strength of superabsorbent composite may be due to synthetical factors such as changes in the crystalline structure and the specific surface area and improvement of the number and the activity of hydroxyl groups of attapulgite, which in turn influence the grafting efficiency of monomer, crosslinking density, and the structure of superabsorbent composite network. POLYM. COMPOS., 28:397–404, 2007. © 2007 Society of Plastics Engineers
Preparative isolation and purification of dicaffeoylquinic acids from the Ainsliaea fragrans champ by high‐speed counter‐current chromatography
Authors: Wang Yingfeng , Liu Bo
Published: May 2007

Two dicaffeoylquinic acids, namely 3,5‐dicaffeoylquinic acid and 4,5‐dicaffeoylquinic acid, have been successfully separated by high‐speed counter‐current chromatography (HSCCC) from an extract of Ainsliaea fragrans Champ, followed by an initial clean‐up step using AB‐8 resin. A two‐phase solvent system composed of chloroform:methanol:water (8:8:4) was selected for the isolation with the aqueous‐rich phase as the stationary phase and the organic‐rich phase as the mobile phase. The developed HSCCC method yielded 34 mg of 3,5‐dicaffeoylquinic acid and 17 mg of 4,5‐dicaffeoylquinic acid from 150 mg of the crude sample in a one‐step separation with purities of 98 and 95%, respectively, as determined by HPLC. The structures of the two compounds were identified from ESI/MS, 1H‐ and 13C‐NMR spectroscopic data. Copyright © 2007 John Wiley & Sons, Ltd.
Absorption‐ and fluorescence‐spectral sensing of alkali metal ions in anionic micelle solutions containing crowned spirobenzopyrans
Authors: Sakamoto H. , Yamamura T. , Takumi K. , Kimura K.
Published: May 2007

Spirobenzopyran derivatives bearing a monoazacrown ether moiety (monoaza‐12‐crown‐4, ‐15‐crown‐5, and ‐18‐crown‐6) and an octadecyl group as a lipophilic moiety, called crowned spirobenzopyrans were synthesized, which can be dissolved in anionic micelle solutions. We examined absorption‐and fluorescence‐spectral changes of micelle solutions containing a crowned spirobenzopyran on addition of alkali metal ions. The crowned spirobenzopyrans are in their merocyanine form in an anionic micelle solution even under dark conditions, showing a significant absorption in the visible region which is attributable to the merocyanine moiety. Crowned spirobenzopyran bearing a monoaza‐12‐crown‐4 moiety exhibited a drastic hypsochromic shift in the absorption and also an enhanced fluorescence on addition of Li+ to the micelle solutions under alkaline conditions. These spectral changes can be attributed to a strong interaction between Li+ bound by the crown ether moiety and a phenolate ion of the merocyanine moiety. Similar absorption and fluorescence‐spectral changes were induced in the anionic micelle solutions containing the other crowned spirobenzopyrans on addition of alkali metal ions. The intensity of the absorption‐spectral changes in the systems of the three crowned spirobenzopyrans, however, differed from each other, depending on the strength of interaction between a metal ion bound to the crown ether moiety and the phenolate ion of the merocyanine moiety. On the other hand, the extent of enhanced relative fluorescence intensity is dependent on the strength of interaction between metal ion and a nitrogen atom of azacrown ether moiety, because the fluorescence spectrum is quenched by photoinduced electron transfer (PET) from the nitrogen atom to the merocyanine moiety. Copyright © 2007 John Wiley & Sons, Ltd.
Copolymerization of vinyl acetate with 1‐octene and ethylene by cobalt‐mediated radical polymerization
Authors: Bryaskova Rayna , Willet Nicolas , Degée Philippe , Dubois Philippe , Jérôme Robert , Detrembleur Christophe
Published: May 2007

The cobalt‐mediated radical polymerization of vinyl acetate was extended to copolymerization with 1‐alkenes (ethylene or 1‐octene). In agreement with the low amount of 1‐alkene that could be incorporated into the copolymer, a gradient structure was predictable, but a rather low polydispersity was observed. A poly(vinyl acetate)‐b‐poly(octene) copolymer was also successfully synthesized, leading to a poly (vinyl alcohol)‐b‐poly(octene) amphiphilic copolymer upon the methanolysis of the poly (vinyl acetate) block. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 2532–2542, 2007
Formation of crystalline inclusion compounds of poly (vinyl chloride) of different stereoregularity with γ‐cyclodextrin
Authors: Martínez Gerardo , Gómez Marián A. , Villar‐Rodil Silvia , Garrido Leoncio , Tonelli Alan E. , Balik C. Maurice
Published: May 2007

This work reports the formation and detailed characterization of the γ‐cyclodextrin (γ‐CD) inclusion compounds (ICs) formed with two poly (vinyl chloride) samples with different isotactic content. The ICs were characterized by X‐ray diffraction, solid state 13C‐NMR, solution 1H‐NMR, FT‐infrared, differential scanning calorimetry, and thermogravimetric analysis. Experimental evidence of the inclusion of the guest polymer chains into the narrow channels created by the γ‐CD crystalline host lattice has been obtained. Examination of coalesced poly (vinyl chlorides) (PVCs) obtained after the host γ‐CD is removed reveals different characteristics specifically for the coalesced PVC sample with higher isotactic content. An increase in Tg was observed by DSC for this PVC. To the contrary, the Tg of the coalesced PVC sample with lower isotactic content is almost the same as that of the as‐synthesized sample. Thermogravimetric analysis indicated that coalesced PVC with higher isotactic content acquires a degree of stabilization after modification by threading into and being extracted from its γ‐CD IC. The results suggest that an irreversible conformational change takes place when PVC forms ICs with a solid host lattice like γ‐CD. The PVC molecules extend and reorganize into a more stable conformation in the IC, consequently improving the properties of the coalesced sample. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 2503–2513, 2007
Polymorphism of nylon‐6 in nylon‐6/nanoclay/functionalized polyolefin blends
Authors: Li Yuying , Hu Xiao
Published: May 2007

The crystallization behavior of Nylon‐6 and the interaction in Nylon‐6/nanoclay/functionalized polyolefin blends were investigated by X‐ray diffraction and Fourier transform infrared spectroscopy. For samples without any thermal history, the interaction between Nylon‐6 and nanoclay or the interaction between Nylon‐6 and functionalized polyolefin favors the formation of γ form crystal. In contrast, the presence of both nanoclay and functionalized polyolefin together in Nylon‐6 was found to have an antagonistic effect on each other's ability to promote the formation of γ form crystal. This was attributed to the complex interactions between the constituents. The crystallization behavior of Nylon‐6 in Nylon‐6/nanoclay/functionalized polyolefin blends is clearly affected by the cointeraction of these effects. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 1494–1502, 2007
Targeting of tumor cells expressing the prostate stem cell antigen (PSCA) using genetically engineered T‐cells
Authors: Morgenroth Agnieszka , Cartellieri Marc , Schmitz Marc , Günes Serap , Weigle Bernd , Bachmann Michael , Abken Hinrich , Rieber Ernst Peter , Temme Achim
Published: May 2007

BACKGROUND

Curative therapeutic options for minimal residual disease or advanced tumor stages in prostate cancer (PCa) are still missing. Adoptive transfer of cytotoxic T‐cells that have been polyclonally rendered tumor‐specific by genetic engineering appears to be a promising immunotherapeutic strategy. Among the numerous prostate tissue/tumor antigens identified during the last years, the “prostate stem cell antigen” (PSCA) is an attractive immunotherapeutic target. It is broadly expressed on the surface of primary PCa cells as well as on PCa metastases.

METHODS

To generate a chimeric T‐cell receptor (TCR) recognizing PSCA, a monoclonal anti‐PSCA antibody was raised and a single‐chain fragment (scFv) was prepared. The resulting anti‐PSCA scFv 7F5 was fused to the β2 constant region derived from the β‐chain of a TCR and to the CD3ζ‐signaling domain.

RESULTS

The chimeric α‐PSCA‐β2/CD3ζ‐TCR, expressed in Jurkat cells, was phosphorylated in the ITAMs of the CD3‐zeta chain upon cross‐linking by insolublized PSCA. When transduced into a mouse cytotoxic T‐cell line, the chimeric receptor specifically activated cytotoxicity against PSCA‐positive tumor cells.

CONCLUSIONS

We developed a functional chimeric TCR against PSCA for treatment of PCa. The chimeric α‐PSCA‐β2/CD3ζ‐TCR might now be used for arming human cytotoxic T‐cells for further studies towards a clinical treatment of PCa. Prostate 67: 1121–1131, 2007. © 2007 Wiley‐Liss, Inc.
An approximate method for calculating transfer integrals based on the ZINDO Hamiltonian
Authors: Kirkpatrick James
Published: May 2007

In this article, we discuss a method for calculating transfer integrals for pairs of molecules based on Zerner's Independent Neglect of Differential Overlap Hamiltonian which requires only a single self‐consistent field calculation on an isolated molecule to be performed to determine the transfer integral for a pair of molecules. This method is compared with results obtained by projection of the pair of molecules' molecular orbitals onto the vector space defined by the molecular orbitals of each isolated molecule. The two methods are found to be in good agreement using three compounds as model systems: pentacene, ethylene, and hexabenzocoronene. © 2007 Wiley Periodicals, Inc. Int J Quantum Chem, 2008
Exact and quantum chemistry‐like calculations in helium doped clusters: The He2Br2(X) example
Authors: Roncero O. , de Tudela R. Pérez , de Lara‐Castells M. P. , Prosmiti R. , Delgado‐Barrio G. , Villarreal P.
Published: May 2007

A quantum chemistry‐like approach has been recently developed in our group to deal with HeN–BC doped helium clusters, where the BC dopant is a conventional diatomic molecule. The central idea is to consider the He atoms as “electrons” while the B and C atoms play the role of the nuclei in standard electronic structure calculations. The procedure provides energies and wavefunctions allowing to perform spectral simulations and, hence, making feasible to do proper comparisons with current experiments. However, because of the large difference of masses of He and electrons, and also to the replacement of Coulomb potentials by molecular interactions, it is worthy to assess to what extent the approximations involved in this model (decoupling of orbital angular momenta of the He atoms from the BC rotation and adiabatic separation of the BC stretch versus the He motions) lead to accurate results. In this work we address these issues on the 4He2–Br2(X) system, containing a couple of bosonic He atoms for which variational calculations can be performed. © 2007 Wiley Periodicals, Inc. Int J Quantum Chem, 2007
Robust absolute stability criteria for uncertain Lur'e systems of neutral type
Authors: Han Qing‐Long , Xue Anke , Liu Shirong , Yu Xinghuo
Published: May 2007

This paper is concerned with robust absolute stability of uncertain Lur'e systems ofneutral type. Somedelay‐dependentstability criteria are obtained and formulated in the form of linear matrix inequalities. The criteria cover some existing results as their special cases. Neithermodel transformationnorbounding techniquefor cross terms is involved through derivation of the stability criteria. Numerical examples show the effectiveness of the criteria. Copyright © 2007 John Wiley & Sons, Ltd.
Assemblies of Carbon Nanotubes and Unencapsulated Sub‐10‐nm Gold Nanoparticles
Authors: Hang Qingling , Maschmann Matthew R. , Fisher Timothy S. , Janes David B.
Published: May 2007

The development of assemblies consisting of unencapsulated, sub‐10‐nm gold particles attached to individual carbon nanotubes (CNTs) with diameters of 2 nm is described. The assemblies are formed on the surface of a porous anodic alumina (PAA) template on which the CNTs (single‐ or double‐walled) are grown by plasma‐enhanced chemical vapor deposition. The Au nanoparticles are formed through an indirect evaporation technique using a silicon nitride membrane mask, and diffuse along the PAA surface into the regions containing CNTs. The nanoparticles bind relatively strongly to the CNTs, as indicated by observations of nanoparticles that are suspended over pores or that move along with the CNTs. This approach may provide a new method to functionalize CNTs for chemical or biological sensing and fundamental studies of nanoscale contacts to CNTs.
Nanorod‐Coated PNIPAM Microgels: Thermoresponsive Optical Properties
Authors: Karg Matthias , Pastoriza‐Santos Isabel , Pérez‐Juste Jorge , Hellweg Thomas , Liz‐Marzán Luis M.
Published: May 2007

Nanoparticles and in particular gold nanorods have interesting optical properties arising from two well‐differentiated plasmon modes. The frequency of such modes can be altered by their chemical environment and coupling with neighboring rods. This study investigates new composite materials made of gold nanorods adsorbed on thermoresponsive poly(N‐isopropylacrylamide) (PNIPAM) microgels. It is shown that the thermally induced collapse of the polymer network inside the particles leads to a red shift of the longitudinal plasmon band of the gold rods, which is found to be fully reversible.
Assessment of the corpus callosum at 20–24 weeks' gestation by three‐dimensional ultrasound examination
Authors: Plasencia W. , Dagklis T. , Borenstein M. , Csapo B. , Nicolaides K. H.
Published: May 2007

Objectives

To determine the range of positions of the fetal head in which a three‐dimensional (3D) volume is acquired for subsequent successful imaging of the corpus callosum.

Methods

We used 3D volumes of the fetal head obtained from singleton pregnancies at 20 to 23 + 6 weeks' gestation. The volumes, which had been acquired with the head in different positions, were then reconstructed with the objective of obtaining a mid‐sagittal section of the brain to demonstrate the presence of the corpus callosum.

Results

In the reconstructed mid‐sagittal sections it was possible to demonstrate the corpus callosum in at least 90% of cases when the 3D volume acquisition plane was (1) mid‐sagittal with the angle between the transducer and the direction of the fetal nose ranging from 0° to 179° and from 330° to 359°, (2) oblique around the crown–rump axis with an angle from the mid‐sagittal plane of less than 30°, (3) oblique around the anteroposterior axis from the axial plane at the level of the biparietal diameter to the mid‐sagittal plane or (4) axial at the level of the biparietal diameter with an angle between the transducer and the midline echo of the brain of 60–119°. In the mid‐sagittal sections either the translucent corpus callosum or a comma‐shaped echogenic structure was seen depending on whether the plane of volume acquisition was sagittal or axial.

Conclusions

In 3D ultrasound examination the extent to which the corpus callosum can be demonstrated to be present is entirely dependent on the plane of volume acquisition. Copyright © 2007 ISUOG. Published by John Wiley & Sons, Ltd.
Efficient duty cycling through prediction and sampling in wireless sensor networks
Authors: Stone Kerri , Colagrosso Michael
Published: May 2007

We present BoostMAC, a CSMA‐based MAC layer protocol for wireless sensor networks that provides an adjustable interface to achieve ultra‐low power operation. To reach low power operation, we adaptively set two radio parameters. First, BoostMAC implements a preamble sampling scheme that allows a mote to dynamically set the length of its duty cycles. Second, we apply machine learning such that a sender can predict its destination's channel polling time and set each outgoing packet's preamble length accordingly. Our two improvements require no extra communication overhead, and each mote in the network implements simple, local models. Energy conservation is one of the most fundamental problems in sensor networks, and by optimizing low‐level operation at the MAC layer, sensor network applications realize an increase in overall performance.

We choose habitat monitoring as a motivating sensor network application because it has unique MAC layer demands, such as fluctuating levels of network traffic. Static configuration at the MAC layer inhibits optimal energy conservation within habitat monitoring applications. We implemented BoostMAC in TinyOS simulator (TOSSIM), and we compare its performance to B‐MAC, a well‐known low power MAC protocol with static behavior. We found that BoostMAC saves energy relative to B‐MAC in bursty networks without affecting latency. Copyright © 2007 John Wiley & Sons, Ltd.
Limited Information Goodness-of-fit Testing in Multidimensional Contingency Tables
Authors: Maydeu-Olivares Albert , Joe Harry
Published: May 2007

We introduce a family of goodness-of-fit statistics for testing composite null hypotheses in multidimensional contingency tables. These statistics are quadratic forms in marginal residuals up to order r. They are asymptotically chi-square under the null hypothesis when parameters are estimated using any asymptotically normal consistent estimator. For a widely used item response model, when r is small and multidimensional tables are sparse, the proposed statistics have accurate empirical Type I errors, unlike Pearson’s X2. For this model in nonsparse situations, the proposed statistics are also more powerful than X2. In addition, the proposed statistics are asymptotically chi-square when applied to subtables, and can be used for a piecewise goodness-of-fit assessment to determine the source of misfit in poorly fitting models.
Erbliches Pankreaskarzinom
Authors: Rieder H.
Published: May 2007

Das duktale Adenokarzinom des Pankreas hat eine äußerst ungünstige Prognose, weil es meist erst in fortgeschrittenen Tumorstadien diagnostiziert wird. Das familiäre Pankreaskarzinom ist ein etabliertes Tumorprädispositionssyndrom, das bei etwa 3% der Pankreaskarzinompatienten beobachtet wird. Die Familienanamnese bei Pankreaskarzinompatienten ist ein wertvolles Instrument, um Personen mit einem erhöhten Risiko für ein Pankreaskarzinom zu identifizieren. Dies ist über die Kombination von Familienanamnese, Mutationssuche in Tumorprädispositionsgenen und die Analyse exogener Risikofaktoren möglich. Bei Hochrisikopersonen könnten invasive Methoden zur Erkennung von Frühstadien eingesetzt und somit eine kurative Pankreatektomie ermöglicht werden. In aktuell laufenden prospektiven Studien wird geprüft, ob auf der Basis klinisch-genetischer Kriterien definierte Hochrisikopatienten von einer Früherkennung des Pankreaskarzinoms profitieren.