bluuebunny/crossref_metadata_2025 huggingface dataset:
Time to Progression in Metastatic Breast Cancer Patients Treated With Epirubicin Is Not Improved by the Addition of Either Cisplatin or Lonidamine: Final Results of a Phase III Study With a Factorial Design
Authors: Berruti Alfredo , Bitossi Raffaella , Gorzegno Gabriella , Bottini Alberto , Alquati Palmiro , De Matteis Andrea , Nuzzo Francesco , Giardina Giorgio , Danese Saverio , De Lena Mario , Lorusso Vito , Farris Antonio , Sarobba Maria Giuseppa , DeFabiani Enza , Bonazzi Giorgio , Castiglione Federico , Bumma Cesare , Moro Gregorio , Bruzzi Paolo , Dogliotti Luigi
Published: October 2002

PURPOSE: To investigate the value of the addition of either cisplatin (CDDP) or lonidamine (LND) to epirubicin (EPI) in the first-line treatment of advanced breast cancer.

PATIENTS AND METHODS: Three hundred seventy-one metastatic breast cancer patients with no prior systemic chemotherapy for advanced disease were randomized to receive either EPI alone (60 mg/m2 on days 1 and 2 every 21 days), EPI and CDDP (30 mg/m2 on days 1 and 2 every 21 days), EPI and LND (450 mg orally daily, given continuously), or EPI, CDDP, and LND. Time to progression, response rates, side effects, and survival were compared according to the 2 × 2 factorial design of this study.

RESULTS: The groups were well balanced with respect to prognostic factors. Time to progression did not differ in the comparison between CDDP arms and non-CDDP arms (median, 10.9 months v 9.4 months, respectively; P = .10) or between that of LND arms and non-LND arms (median, 10.8 months v 9.9 months, respectively; P = .47), nor did overall survival. The response rate did not significantly differ in the comparison between LND arms and non-LND arms (62.9% v 54.0%, P = .08). No difference in treatment activity was observed between CDDP arms and non-CDDP arms. Toxicity was significantly higher in the CDDP arms, leading to CDDP dose adjustment in 40% of cases. The most frequent side effects were of a hematologic and gastrointestinal nature. The addition of LND produced more myalgias and fatigue.

CONCLUSION: Neither CDDP nor LND was able to significantly improve the time to progression obtained by EPI. CDDP, however, significantly worsened the drug’s tolerability.
Interim Comparison of a Continuous Infusion Versus a Short Daily Infusion of Cytarabine Given in Combination With Cladribine for Pediatric Acute Myeloid Leukemia
Authors: Crews Kristine R. , Gandhi Varsha , Srivastava Deo Kumar , Razzouk Bassem I. , Tong Xin , Behm Fred G. , Plunkett William , Raimondi Susana C. , Pui Ching-Hon , Rubnitz Jeffrey E. , Stewart Clinton F. , Ribeiro Raul C.
Published: October 2002

PURPOSE: To identify the optimal schedule for infusion of cytarabine (ara-C) given with cladribine (2-CdA) to pediatric patients with acute myeloid leukemia (AML), and to compare the effects of the two schedules on the pharmacokinetics of ara-C triphosphate (ara-CTP) in leukemic cells.

PATIENTS AND METHODS: Forty-nine pediatric patients with newly diagnosed primary AML received a 5-day course of ara-C 500 mg/m2/d and 2-CdA 9 mg/m2/d. They were randomly assigned to receive ara-C as either a 2-hour daily infusion (arm A) or a continuous infusion (arm B). Cellular pharmacokinetics were studied on days 1 and 2. All patients then received two courses of remission induction chemotherapy with daunorubicin, ara-C, and etoposide (DAV).

RESULTS: Thirty-two percent of patients (seven of 22) in arm A and 63% (17 of 27) in arm B entered complete remission (P = .045) after ara-C and 2-CdA therapy. Coadministration of 2-CdA increased the intracellular concentration of ara-CTP in 20 of 36 patients, although we found no statistically significant difference between the treatment arms in this effect (P = .63). The incidence of toxicity did not differ significantly between the two treatment arms (P = .53). After two courses of DAV, the rate of complete remission was 91% in arm A and 96% in arm B (P = .58).

CONCLUSION: Intracellular accumulation of ara-CTP is increased when 2-CdA is given with ara-C, but no schedule-dependent differences in this effect were seen. The combination of 2-CdA and ara-C seems to be effective therapy for pediatric AML.
Hormonal influence on the release of endothelial nitric oxide: gender-related dimorphic sensitivity of rat aorta for noradrenaline
Authors: Calderone Vincenzo , Baragatti Barbara , Breschi Maria Cristina , Nieri Paola , Martinotti Enrica
Published: October 2002

Male gender shows a higher incidence of vascular disorders and this phenomenon could be explained by sexual dimorphic behaviour of vessels. Both gonadal hormones and endothelial nitric oxide (NO) are involved in the regulation of the vascular reactivity. This study aimed to evaluate a possible sexual dimorphic sensitivity of rat aorta for the catecholamine noradrenaline. To understand the role played by physiological concentrations of sex hormones, the experimental procedures were performed on isolated preparations from intact (sham-operated) and gonadectomized rats of both sexes. In parallel sets of experiments, the biosynthesis of NO was inhibited by Nω-nitro-l-arginine methyl ester (L-NAME) to reveal any potential involvement of the endothelial modulator and its possible link with the endocrinous factor. In aortae from intact male and female rats, noradrenaline induced contractile effects with different potencies (mean ± s.d. EC50 values 12.15 ± 5.25 nM and 84.10 ±18.68 nM, respectively). Gonadectomy resulted in an increased sensitivity for noradrenaline in female vessels and a decreased sensitivity for the agonist in male vessels (EC50 values 25.64 ± 5.04 nM and 21.70 ± 11.13 nM, respectively). In aortae from intact male rats, the inhibition of NO biosynthesis resulted in a weak increase in sensitivity for noradrenaline (EC50 value 6.08 ±4.53 nM), whereas the increase was higher in vessels from intact female rats (EC50 value 10.38 ± 8.40 nM). After treatment with L-NAME, aortae from gonadectomized male and female rats presented almost equivalent increases in sensitivity for the adrenergic agonist (EC50 values 6.02 ± 3.63 nM and 9.10 ± 9.63 nM, respectively), and no significant difference in sensitivity could be recorded between intact and orchidectomized male rats, or between intact and ovariectomized female rats. It was concluded that rat aorta showed a sexual dimorphic sensitivity for noradrenaline and the female sex was more protected against the adrenergic contractile stimulus because of a higher release of endothelial NO. The gender-related difference in NO release was influenced by gonadal hormones, with the female hormones inducing an increase and the male hormones causing a reduction.
Some optimal stopping problems with nontrivial boundaries for pricing exotic options
Authors: Guo Xin , Shepp Larry
Published: October 2002

We solve the following three optimal stopping problems for different kinds of options, based on the Black-Scholes model of stock fluctuations. (i) The perpetual lookback American option for the running maximum of the stock price during the life of the option. This problem is more difficult than the closely related one for the Russian option, and we show that for a class of utility functions the free boundary is governed by a nonlinear ordinary differential equation. (ii) A new type of stock option, for a company, where the company provides a guaranteed minimum as an added incentive in case the market appreciation of the stock is low, thereby making the option more attractive to the employee. We show that the value of this option is given by solving a nonalgebraic equation. (iii) A new call option for the option buyer who is risk-averse and gets to choose, a priori, a fixed constant l as a ‘hedge’ on a possible downturn of the stock price, where the buyer gets the maximum of l and the price at any exercise time. We show that the optimal policy depends on the ratio of x/l, where x is the current stock price.
The coupon subset collection problem
Authors: Adler Ilan , Ross Sheldon M.
Published: October 2002

The coupon subset collection problem is a generalization of the classical coupon collecting problem, in that rather than collecting individual coupons we obtain, at each time point, a random subset of coupons. The problem of interest is to determine the expected number of subsets needed until each coupon is contained in at least one of these subsets. We provide bounds on this number, give efficient simulation procedures for estimating it, and then apply our results to a reliability problem.
A new discrete distribution arising in a model of DNA replication
Authors: Cowan Richard
Published: October 2002

During DNA replication, small fragments of DNA are formed. These have been observed experimentally and the mechanism of their formation modelled mathematically. Using the stochastic model of Cowan and Chiu (1992), (1994), we find the probability distribution of the number of fragments. A new discrete distribution arises. The work has interest as an application of the recent theory on quasirenewal equations in Piau (2000).
Random walk in a random environment with correlated sites
Authors: Komorowski T. , Krupa G.
Published: October 2002

We prove the law of large numbers for random walks in random environments on the d-dimensional integer lattice Zd. The environment is described in terms of a stationary random field of transition probabilities on the lattice, possessing a certain drift property, modeled on the Kalikov condition. In contrast to the previously considered models, we admit possible correlation of transition probabilities at different sites, assuming however that they become independent at finite distances. The possible dependence of sites makes impossible a direct application of the renewal times technique of Sznitman and Zerner.
A probabilistic proof of non-explosion of a non-linear PDE system
Authors: López-Mimbela J. Alfredo , Wakolbinger Anton
Published: October 2002

Using a representation in terms of a two-type branching particle system, we prove that positive solutions of the system remain bounded for suitable bounded initial conditions, provided A and B generate processes with independent increments and one of the processes is transient with a uniform power decay of its semigroup. For the case of symmetric stable processes on R1,this answers a question raised in [4].
Generalized reliability bounds for coherent structures
Authors: Boutsikas Michael V. , Koutras Markos V.
Published: October 2002

In this article we introduce generalizations of several well-known reliability bounds. These bounds are based on arbitrary partitions of the family of minimal path or cut sets of the system and can be used for approximating the reliability of any coherent structure with i.i.d. components. An illustration is also given of how the general results can be applied for a specific reliability structure (two-dimensional consecutive-k1 x k2-out-of-n1x n2 system) along with extensive numerical calculations revealing that, in most cases, the generalized bounds perform better than other available bounds in the literature for this system.
A note on the rate of convergence to equilibrium for Erlang's model in the subcritical case
Authors: Voit Michael
Published: October 2002

We derive some asymptotic results for the rate of convergence to equilibrium for the number of busy servers in an M/M/N/N queue with input rate λN and service rate 1 for N → ∞ in the ‘subcritical’ case λ ∈]0, 1[. These results improve recent contributions of Fricker, Robert and Tibi.
Optimal investment strategies in a CIR framework
Authors: Deelstra Griselda , Grasselli Martino , Koehl Pierre-François
Published: October 2002

We study an optimal investment problem in a continuous-time framework where the interest rates follow Cox-Ingersoll-Ross dynamics. Closed form formulae for the optimal investment strategy are obtained by assuming the completeness of financial markets and the CRRA utility function. In particular, we study the behaviour of the solution when time approaches the terminal date.
Power-law correlations, related models for long-range dependence and their simulation
Authors: Gneiting Tilmann
Published: October 2002

Martin and Walker ((1997)J. Appl. Prob.34,657–670) proposed the power-law ρ(v) =c|v|-β, |v| ≥ 1, as a correlation model for stationary time series with long-memory dependence. A straightforward proof of their conjecture on the permissible range ofcis given, and various other models for long-range dependence are discussed. In particular, the Cauchy family ρ(v) = (1 + |v/c|α)-β/αallows for the simultaneous fitting of both the long-term and short-term correlation structure within a simple analytical model. The note closes with hints at the fast and exact simulation of fractional Gaussian noise and related processes.
Non-product form of two-dimensional fluid networks with dependent Lévy inputs
Authors: Kella Offer
Published: October 2002

We show that the stationary distribution of a two-dimensional stochastic fluid network with (possibly dependent) Lévy inputs does not have product form other than in truly obvious cases. This is in contrast to queueing networks, where product form exists for non-obvious situations in which the inputs are independent, and for Brownian networks, where it typically exists for cases where the driving processes are actually dependent.
A note on the ℒ-class of life distributions
Authors: Klar B.
Published: October 2002

This paper first recalls some stochastic orderings useful for studying the ℒ-class and the Laplace order in general. We use these orders to show that the higher moments of an ℒ-class distribution need not exist. Using simple sufficient conditions for the Laplace ordering, we give examples of distributions in the ℒ- and ℒα-classes. Moreover, we present explicit sharp bounds on the survival function of a distribution belonging to the ℒ-class of life distributions. The results reveal that the ℒ-class should not be seen as a more comprehensive class of ageing distributions but rather as a large class of life distributions on its own.
The common ancestor at a nonneutral locus
Authors: Fearnhead Paul
Published: October 2002

We consider a nonneutral population genetics model with parent-independent mutations and two selective classes. We calculate the stationary distribution of the type of the common ancestor of a sample of genes from this model. The expected fitness of any ancestor (including the most recent common ancestor of any sample) is shown to be greater than the expected fitness of a randomly chosen gene from the population. The process of mutations to the common ancestor is also analysed. Our results are related to, but more general than, results obtained from diffusion theory.
Hawkes branching point processes without ancestors
Authors: Brémaud Pierre , Massoulié Laurent
Published: October 2002

In this article, we prove the existence of critical Hawkes point processes with a finite average intensity, under a heavy-tail condition for the fertility rate which is related to a long-range dependence property. Criticality means that the fertility rate integrates to 1, and corresponds to the usual critical branching process, and, in the context of Hawkes point processes with a finite average intensity, it is equivalent to the absence of ancestors. We also prove an ergodic decomposition result for stationary critical Hawkes point processes as a mixture of critical Hawkes point processes, and we give conditions for weak convergence to stationarity of critical Hawkes point processes.
Coalescent theory for seed bank models
Authors: Kaj Ingemar , Krone Stephen M. , Lascoux Martin
Published: October 2002

We study the genealogical structure of samples from a population for which any given generation is made up of direct descendants from several previous generations. These occur in nature when there are seed banks or egg banks allowing an individual to leave offspring several generations in the future. We show how this temporal structure in the reproduction mechanism causes a decrease in the coalescence rate. We also investigate the effects of age-dependent neutral mutations. Our main result gives weak convergence of the scaled ancestral process, with the usual diffusion scaling, to a coalescent process which is equivalent to a time-changed version of Kingman's coalescent.
Multivariate product-type lower bounds
Authors: Block Henry W. , Chen Tuhao
Published: October 2002

Univariate probability inequalities have received extensive attention. It has been shown that under certain conditions, product-type bounds are valid and sharper than summation-type bounds. Although results concerning multivariate inequalities have appeared in the literature, product-type bounds in a multivariate setting have not yet been studied. This note explores an approach using graph theory and linear programming techniques to construct product-type lower bounds for the probability of the intersection among unions of k sets of events.
Physical activity across the cancer continuum: Report of a workshop
Authors:   The Scientific Program Committee
Published: October 2002

This article summarizes the results of a workshop that reviewed existing knowledge of the role of physical activity across the cancer continuum. Innovative designs for future research from the basic to the population‐based level are discussed.
Prognostic value of plasma interleukin‐6 levels in patients with chronic lymphocytic leukemia
Authors: Lai Raymond , O'Brien Susan , Maushouri Taghi , Rogers Anna , Kantarjian Hagop , Keating Micheal , Albitar Maher
Published: October 2002

BACKGROUND

Interleukin 6 (IL‐6) is a B‐cell growth and differentiation factor, which may promote the growth of B‐cell neoplasms. In chronic lymphocytic leukemia (CLL) patients, IL‐6 plasma levels increased in a stage‐dependent manner, suggesting that IL‐6 may be a useful prognostic marker. The purpose of this study is to fully assess the prognostic value of IL‐6 in CLL patients.

METHODS

We measured the plasma levels of IL‐6 in 100 CLL patients using an enzyme‐linked immunoassay method.

RESULTS

Increasing levels of IL‐6 significantly correlated with patient age, severity of anemia, Rai stage, white cell count, and β‐2‐microglobulin (β‐2M). Although CLL patients did not differ significantly from the normal controls in the median IL‐6 plasma level (P = 0.38), patients with advanced diseases (defined by Rai stage III/IV or β‐2M > 3.5) had a significantly higher median IL‐6 plasma level than the normal controls (P < 0.05). Furthermore, in patients with advanced diseases, Cox regression hazards model showed that a higher IL‐6 level correlated with shorter survival (P = 0.0001). Using IL‐6 level of 3 pg/mL as a cutoff, patients with low IL‐6 levels had a significantly longer overall survival than those with high IL‐6 levels (log rank test, P = 0.002). In patients with CD38‐positive CLL, patients with high IL‐6 levels (> 3 pg/mL) had significantly shorter survival (P = 0.03). To conclude, IL‐6 is a particularly useful predictor for survival in CLL patients with advanced diseases.

CONCLUSIONS

Our findings suggest that patients with advanced‐stage CLL as well as high IL‐6 plasma levels may require aggressive therapeutic approaches and special consideration for experimental therapy. Cancer 2002;95:1071–5. © 2002 American Cancer Society.

DOI 10.1002/cncr.10772
Financial analysis of patients with newly diagnosed acute myelogenous leukemia on protocol or standard therapy
Authors: Berman Ellin , Little Claudia , Teschendorf Bonnie , Jones Meaghan , Heller Glenn
Published: October 2002

BACKGROUND

Medicare and third‐party payers may be reluctant to pay for investigational (protocol) therapy for patients with cancer on the premise that such treatment is more expensive than standard therapy. However, prior studies that have attempted to compare protocol therapy with standard therapy have been difficult to interpret because of the assortment of malignancies studied and the lack of suitable control groups of patients who received standard therapy.

METHODS

In the current study, the authors conducted a retrospective review of the financial charges associated with protocol or nonprotocol (standard) chemotherapy in patients with a single malignancy, newly diagnosed acute myelogenous leukemia (AML), who received their initial course of chemotherapy (“induction”) at the Memorial Sloan‐Kettering Cancer Center (MSKCC) between 1996 and 1999. Protocol and nonprotocol groups were analyzed according to clinical characteristics and standard prognostic features to determine whether the two groups were comparable. Median charges for all patients were determined using a database that linked clinical information, financial data, and clinical outcomes.

RESULTS

A total of 353 patients with newly diagnosed AML were registered at MSKCC during the time period studied; of these, 79 patients (22%) received all of their care at the institution. Thirty patients (38%) received treatment on an investigational protocol. Forty‐nine patients (62%) did not receive protocol therapy for the following reasons: 10 patients (20%) did not meet eligibility criteria, 4 patients (8%) were eligible for protocol therapy but declined, and 35 patients (71%) met protocol criteria but were not offered protocol therapy based on the judgment of their primary oncologist. The groups were not comparable because patients treated with standard therapy were older and had a poorer initial Eastern Cooperative Oncology Group (ECOG) performance status. Overall median charges for patients in the nonprotocol group were higher than for patients treated on a protocol although charges were not related to age, initial ECOG performance status, or cytogenetic risk group.

CONCLUSIONS

Although charges for the nonprotocol group were higher, specific factors responsible for this difference were not identified. This study emphasizes the problems inherent in assembling suitable groups of patients for comparison. Cancer 2002;95:1064–70. © 2002 American Cancer Society.

DOI 10.1002/cncr.10805
Characterization of measles sequences from Pune, India
Authors: Wairagkar Niteen , Rota Paul A. , Liffick Stephanie , Shaikh Naseem , Padbidri V.S. , Bellini William J.
Published: October 2002

The goal of this study was to conduct the initial genetic characterization wild‐type measles viruses currently circulating in India. Reverse transcription‐polymerase chain reaction detected measles RNA in 11 of 14 throat swabs collected from sporadic and outbreak‐associated cases in the city of Pune, during 1996–1998. Sequence analysis of the H and N genes showed that six sequences were genotype D4, three were genotype D8, and two were genotype A. Continued virologic surveillance in other areas of India as well as neighboring countries will indicate the extent of genetic diversity present among wild‐type measles viruses circulating in India. J. Med. Virol. 68:611–614, 2002. © 2002 Wiley‐Liss, Inc.
Priority rules for check processing in multiple branch banking: An experimental analysis
Authors: Mabert Vincent A. , Showalter Michael J.
Published: October 2002

The check‐processing activity represents a major function in a commercial bank. If checks are quickly processed through the bank, then funds will be transferred to appropriate accounts and the bank will experience minimum float. This paper discusses the use of priority rules to maximize the dollar value of checks processed each day. A series of experiments are developed to test a set of priority rules (heuristics) under different operating conditions of check processing capacity, transit dollar levels, and branch characteristics. The results indicate that significant differences in performance are present for different rules. Also, the usefulness of some rules are dependent upon the commercial bank's operating characteristics, which has important implications for operating managers.
An optimal inventory model where resupply is possible but uncertain
Authors: Haber Sheldon E. , Sitgreaves Rosedith
Published: October 2002

A model is formulated for computing the optimal stock quantity of an item when resupply is possible but uncertain. The distinguishing feature of the model is that the optimal stock quantity calculation takes into account the cost of resupply and the probability of stock arriving by a specified mode of transport in time for issue to customers. The model is then applied to the problem of determining a preferred mode of transport for an assumed set of parameters.
A requirements planning system for the Space Shuttle Operations schedule
Authors: Steinberg Earl , Lee William B. , Khumawala Basheer M.
Published: October 2002

The National Aeronautics and Space Administration (NASA) is charged with developing a Flight Operations Planning Schedule for Space Shuttle Operations in the 1980s. During this decade, NASA plans to launch up to thirty space shuttle flights per year when the program reaches the mature phase. Traditional planning techniques for space flights (PERT‐type models) are inadequate for this task because of their inability to resolve conflicts arising from multiple demands for limited resources generated by numerous simultaneous projects (space flights). This paper describes a requirements planning system developed by the authors and adopted by NASA for this resource constrained multiple project scheduling problem.
Improving fuel utilization in steel mill operations using linear programming
Authors: Markland Robert E.
Published: October 2002

This paper describes the use of linear programming to improve the fuel utilisation at a major Midwestern steel mill. In particular, linear programming is used to determine an efficient fuel allocation plan for this steel mill, which reduces the total fuel costs for the steel mill operations. The efficient fuel allocation plan that is developed utilises two externally purchased fuels: natural gas and fuel oil, and two gases: blast furnace gas and coke plant gas, which are internally generated as natural by‐products of the production process. Test results from the application of the linear programming model are presented and discussed, and indicate that considerable cost savings can be achieved by utilizing a fuel allocation plan which more effectively utilizes the by‐product gases which are produced within the steel making process.
Work force scheduling for arbitrary cyclic demands
Authors: Bechtold Stephen E.
Published: October 2002

The problem considered here is the determination of the minimum full‐time workforce and corresponding work schedule to meet arbitrary cyclic staffing requirements where all workers are idle either one or two consecutive periods per cycle. Specialized algorithms are developed which are less complex and consequently more efficient than existing algorithms. The new algorithms are also compared with alternative algorithms on the basis of slack dispersion which is a criterion that has not been previously considered in the literature. The results suggested the existence of a trade‐off between the execution efficiency of the algorithms and their slack dispersion characteristics. Some initial framework required for future research is also provided.
Design of an interrelated quality system for a single product manufacturing process with assembly
Authors: Knowles Thomas W. , Hassan M.Zia
Published: October 2002

The design of a single product manufacturing system with assembly is considered. The processing is on a lot‐by‐lot basis with the lot size fixed. The decision variables include interrelated single sampling plans, manufacturing process quality levels, incoming raw material quality levels and assembly process quality levels. A solution procedure is given to minimize the expected total of the costs associated with the quality of the finished product subject to a limit on the Average Outgoing Quality Limit of the finished product. An example is provided.
Hierarchical integration in production planning: Theory and practice
Authors: Gelders Ludo F. , Van Wassenhove Luk N.
Published: October 2002

This paper discusses the issue of integrating various decision levels in hierarchical production planning systems. First the theory is briefly reviewed and then two case studies are presented. It is argued that it is not sufficient to have a good decision model at every level of the decision hierarchy. The different models should be carefully integrated. The potential problems resulting from a lack of integration are discussed. These problems are then illustrated in two case studies in order to be able to focus on actual managerial issues. It is shown how different decision levels supported by decision models were integrated in these two applications. Two important features are the crucial role of crossfunctional managerial committees in the integration process and the introduction of slack to avoid disaggregation problems.

We do not claim to be exhaustive in presenting the problems related to integration nor do we claim that the solutions to the cases are the best possible ones. We do, however, hope that this paper motivates production managers to take a serious look at their hierarchical planning procedures.
Application of work center control rules in a job shop environment
Authors: Fisk John C. , Segal John P.
Published: October 2002

Work center control rules, defined as a combination of job dispatch rules and short‐term work center capacity adjustments, are analyzed using queueing theory. Promising rules are evaluated with a job shop simulation model. Simulations comparing work center control rules to the critical ratio rule for job dispatching indicate that work center control can increase performance to customer due date while simultaneously reducing average work in process inventory. The work center control rules are easily implemented by shops currently using input/output control and daily dispatch lists.
The part‐period balancing algorithm and its look ahead‐look back feature: A theoretical and experimental analysis of a single stage lot‐sizing procedure
Authors: Wemmerlöv Urban
Published: October 2002

This paper investigates the discrete Part‐Period Balancing (PPB) lot‐sizing algorithm and its optional feature, the Look Ahead‐Look Back tests. PPB is the most commonly used dynamic lot‐sizing procedure in practice and it has also been tested extensively in simulation experiments. Although its overall cost performance, relative to other heuristics, have been fairly good, a fundamental flaw with the model has been noted in the literature. This deficiency leads to poor performance under certain conditions.

In this paper a simple adjustment to the main algorithm is analytically derived under the assumptions of a constant demand rate and an infinite planning horizon. The adjustment leads to an optimal behavior for the PPB heuristic under the stated conditions. Subsequent experimental analysis through simulation of lot‐sizing performance in environments with time‐varying, discrete demand shows that the proposed adjustment leads to significant cost reductions.

This paper also analyzes the Look Ahead‐Look Back tests which is the distinguishing feature between the PPB procedure and the Least Total Cost algorithm. The tests were devised to improve the cost performance of the PPB heuristic by marginally adjusting each tentative lot‐size. The effect of the Look Ahead‐Look Back tests have, however, never been verified in the literature. The tests have undergone some changes over time, when they have been included in commercial software packages for inventory management. We suggest yet another modified version in this paper.

In the last portion of the paper, the cost effectiveness of the Look Ahead‐Look Back tests is confirmed through simulation. That is, when used together with the original PPB procedure, they lead to an improved cost performance. It is also shown that a combination of these tests and the adjustment to the PPB procedure mentioned earlier leads to an even lower average total cost. All cost improvements are statistically significant. It is finally noted that the Look Ahead‐Look Back tests perform poorly in certain constant demand situations. Additional analytic and experimental analysis shows that these results stem from a dominance of the Look Back test over the Look Ahead test, leading to the former test being performed more often. This can easily be corrected, however, by checking for sufficient variability in the data before the Look Back test is employed.
Aggregate planning in health care foodservice systems with varying technologies
Authors: Connell Bertrum C. , Adam Everett E. , Moore Aimee N.
Published: October 2002

The health care delivery system has been criticized widely for ineffective cost control, excessive pricing, and poor productivity. It is clear that a segment of the United States economy has continued to be inflationary the past few years.

The health care foodservice system is expected to meet the daily food and nutritional needs of patients, employees, and visitors throughout the year. Some of the difficult‐and potentially costly‐management decisions involve establishing staffing levels and food production rates to meet this changing demand.

The purpose of this investigation was to evaluate two heuristic aggregate planning models in three types of health care food production systems to determine if the models were more effective in cost reduction than the management decisions which were made. The Search Decision Rule (SDR) and Management Coefficients Model (MCM) were selected based upon previous testing in industrial applications. In each of three different hospital food systems‐conventional, cook‐chill, and minimal cooking‐the aggregate plan decision rules (from the models) were compared with the hospital's master labor schedule over a one year test period. Cost of implementing the decision rules and the existing master labor schedule was determined using an objective cost function derived from cost records in each foodservice system.

The SDR model performed statistically better than the MCM and the existing master labor schedule provided by management. SDR model performance depended upon the technology in which it was applied, providing the greatest savings in the conventional foodservice technology. Potential annual dollar savings between the hospital's existing master labor schedule and the SDR for each foodservice system varied from $74,329 to $182,487.

Implementation of the SDR model could help the foodservice administrator be more effective in scheduling expensive labor resources by determining in advance decision rules that will simultaneously meet production demand and significantly reduce cost. The major resistances to implementation are expected to be lack of model understanding and the resistance to trusting a computerized model where the potential for some food shortage will still exist, even though it exists now with manual scheduling systems.
MRP with high uncertain yield losses
Authors: New Colin , Mapes John
Published: October 2002

Certain manufacturing systems, notably those in high technology precision casting and integrated circuit production suffer from process yield losses which are both significant in quantity terms and are also highly unpredictable. This poses special problems for the provisioning of materials to support a manufacturing program and for the detailed scheduling necessary to update the priorities of work in process batches as losses occur. This paper establishes a framework of analysis to handle this problem in MRP logic. It describes the mechanisms available and discusses their relevance to the market environments in which the company is operating.

The key conclusion of this paper is that different solutions are required for different market circumstances. The four key strategies developed are:

A: For continuous schedules, make‐for‐stock: Use mean yield rate and fixed buffer stocks.

B: For continuous schedules, make‐to‐order: Use mean yield rate, fixed buffers and a yield to finish monitoring system.

C1: For single batch production make‐to‐order: As for B but using a desired service level yield rate.

C2: For multiple batch production, make‐to‐order: As B but using a variable yield rate by batch.

The implementation of each of these is described in relation to the business objectives of cost effectiveness and customer satisfaction.
Resolving uncertainty in manufacturing systems
Authors: Schmitt Thomas G.
Published: October 2002

This paper examines the effectiveness of three commonly practiced methods used to resolve uncertainty in multi‐stage manufacturing systems: safety stock under regenerative material requirements planning (MRP) updates, safety capacity under regenerative MRP updates, and net change MRP updates, i.e., continuous rather than regenerative (periodic) updates. The use of safety stock reflects a decision to permanently store materials and labor capacity in the form of inventory. When unexpected shortages arise between regenerative MRP updates, safety stock may be depleted but it will be replenished in subsequent periods. The second method, safety capacity, overstates the MRP capacity requirements at the individual work centers by a prescribed amount of direct labor. Safety capacity either will be allocated to unanticipated requirements which arise between MRP regenerations or will be spent as idle time. The third method, net change, offers a means of dealing with uncertainty by rescheduling instead of buffering, provided there is sufficient lead time to execute the changes in the material and capacity plans.

Much of the inventory management research has addressed the use of safety stock as a buffer against uncertainty for a single product and manufacturing stage. However, there has been no work which evaluates the performance of safety stock relative to other resolution methods such as safety capacity or more frequent planning revisions. In this paper, a simulation model of a multi‐stage (fabrication and assembly) process is used to characterize the behavior of the three resolution methods when errors are present in the demand and time standard estimates. Four end products are completed at an assembly center and altogether, the end products require the fabrication of twelve component parts in a job shop which contains eight work centers. In addition to the examination of the three methods under different sources and levels of uncertainty, different levels of bill of material commonality, MRP planned lead times, MRP lot sizes, equipment set‐up times and priority dispatching rules are considered in the experimental design.

The simulation results indicate that the choice among methods depends upon the source of uncertainty, and costs related to regular time employment, employment changes, equipment set ups and materials investment. For example, the choice between safety stock and safety capacity represents a compromise between materials investment and regular time employment costs. The net change method is not designed to deal effectively with time standard errors, although its use may be preferred over the two buffering alternatives when errors are present in the demand forecasts and when the costs of employment changes and equipment set ups are low. The simulation results also indicate that regardless of the method used, efforts to improve forecasts of demands or processing times may be justified by corresponding improvements in manufacturing performance.
Planning horizons for master production scheduling
Authors: Chung Chen‐Hua , Krajewski Lee J.
Published: October 2002

Production and operations planning in organizations quite often is a multi‐level sequential process, involving aggregate planning, master production scheduling, and detailed operations planning and scheduling. To obtain good planning results, it is desirable to have a proper planning horizon for each level of planning. There have been a considerable number of studies dealing with planning horizons for aggregate planning or production smoothing problems. There are also many planning horizon studies for single‐item lot sizing problems. No study has addressed the issues associated with the planning horizons for master production schedules (which is a multi‐item lot sizing problem in nature), particularly with respect to the relationship to the aggregate plan.

This study addresses the issue of planning horizons for companies employing a make‐to‐stock competitive strategy facing a seasonal demand for their products. We formulate the aggregate planning problem and the master scheduling problem as two separate mathematical programs to approximate the two‐stage process that typically takes place in practice. Rolling planning horizons are used to approximate the periodic updates of the plans commonly done in practice. The models also incorporate resource requirements planning concepts to estimate loads on the critical work centers.

The planning process is simulated as a single pass procedure where the results of aggregate planning are passed to the master production scheduling model once per month and the results of the master scheduling model (i.e., the portion of the master schedule actually implemented) are passed back to the aggregate planning model for the next planning session.

The experimental results show that when the planner faces extreme cost structures such as high smoothing costs/high setup costs or low smoothing costs/low setup costs, the planning horizon effects are reduced to a minimum. Master schedule planning horizons need not be as long as aggregate planning horizons. Alternatively, non‐extreme cost structures such as high smoothing costs/low setup costs and low smoothing costs/high setup costs should be handled with equal planning horizons for both aggregate planning and master scheduling.

It is also found that the firm's cost structure has an impact on the appropriate planning horizon for both aggregate planning and master scheduling. Some cost conditions allow for smaller master schedule horizons. The best horizon choice seems to be equal planning horizons for both aggregate planning and master scheduling, even though the cost savings is slight in some cases.

Finally, the proper length of the planning horizon for master scheduling is affected by the planning horizon of the aggregate plans.
The complementary nature of manufacturing goals by their relationship to throughput time: A theory of internal variability of production systems
Authors: Wacker John G.
Published: October 2002

This study argues that major manufacturing goals are compatible due to their relationships with internal throughput time which, in turn, depends upon estimated parameters. Further, this study argues that a large percentage of the internal throughput time is caused by variable move, queue, or preventive maintenance policies that introduce uncertainty into the manufacturing system, requiring internal buffer inventories to accumulate in the queue and increase throughput time. The increase in throughput time decreases production performance by creating higher inventories and lower productivity and a general decrease in the manufacturing performance.

The results of this study suggest that internal variability of throughput time is caused by both variability of move times and processing time. Further, processing variability can be improved by lower rework time and lower down time, both of which may be achieved by systematic preventive maintenance programs.

The results also suggest the protection of the “technical core” from demand variations is necessary for modern just‐in‐time systems. Further, they suggest that if the technical core is not protected, internal buffer queues may develop and further worsen system performance by increasing costs and decreasing on‐time delivery.

This study's results support common practitioner concern about quality and its relationship to the success of just‐in‐time systems. In short, this study provides a theoretical base that justifies the results of other studies and practitioners' experiences with modern production facilities.
Alternative master production scheduling techniques in an assemble‐to‐order environment
Authors: King Barry E. , Benton W.C.
Published: October 2002

The manufacturer's ability to respond quickly and with great flexibility is crucial. The future belongs to the manufacturer of high tech, high‐value products who can compress not only component and assembly process times, but design and tooling cycles as well. Master production scheduling provides a road map for production requirements.

This article reports the results of a simulation study that compares alternative procedures for determining master production scheduling (MPS) techniques utilizing the superbill and covering set MPS. The performance criterion for the study is the available‐to‐promise (ATP) lead time (customer service). The results of the simulation experiment support the superiority of the superbill technique over the covering set technique in terms of customer service. The penalty associated with using the more efficient covering set technique as an alternative to the well known superbill technique is a significant decline in customer service. However, covering sets have computational advantages that must be considered, especially when the MPS procedures have to be repeated routinely. Finally areas for future research are suggested. It is especially important that a trade‐off between the customer service and manufacturing flexibility be investigated.
A procedure for dealing with multiple objectives in cell formation decisions
Authors: Frazier Gregory V. , Gaither Norman , Olson David
Published: October 2002

A procedure for dealing with multiple objectives in cell formation decisions is proposed. Theoretical foundations from multiobjective decision making have been utilized to provide a framework for the study. The purpose of the study is to develop a procedure that provides managers with a means of developing multiple objective cell formation decisions as an alternative to intractable integer programming models. We use a best of random seeds heuristic to generate a large number of alternatives. Nondominated solution theory is used to develop a list of potentially useful alternatives. Finally, preference cone theory is used to aid decision maker selection from these nondominated alternatives. Each of these three technologies have been developed elsewhere. This study considers aspects of applying these technologies to cell formation decisions. The procedure and its theoretical underpinnings are explained step‐by‐step and illustrated in a four‐objective, four‐cell, 24‐machine, and 50‐part cell formation problem. The example contains 12 nondominated solutions and requires only four pairwise comparisons of nondominated solutions by a decision maker before convergence to the preferred solution. Computer processing requirements are not burdensome, and decision maker participation is expected to be efficient.
A conceptual model for demand management in the assemble‐to‐order environment
Authors: Kern Gary M. , Guerrero Hector H.
Published: October 2002

The term demand management encompasses the activities required to accept customer orders and promise them productive capacity. This activity is central to effective manufacturing planning and control. The popularity of just‐in‐time systems suggests that manufacturers are steadily losing authority for establishing order delivery dates, further confounding the demand management process. No reported research has suggested how this process can be performed.

This paper presents a rigorous description of the demand management process in the assemble‐to‐order environment, as a mathematical model. The description provided in this model should be viewed as an initial attempt to define the complex challenges that arise in dealing with demand management on an operational level. The focus of this model is short‐term decision making involved in controlling demand management—accepting orders and dispatching capacity to fill the orders.

The problem is presented in the context of the assemble‐to‐order environment which requires the monitoring of both a final assembly schedule and a master production schedule. The factors involved in effective decision making for demand management including capacity availability, relative costs, and the relative timing of prospective customer orders are discussed. A simple example is presented to illustrate the performance of the mathematical model.