Cleanup Phase Research Articles

Improving project management “closeout” phase outcomes: evidence from a large general contractor in Iran using “X-inefficiency theory”

PurposeOptimal clean-up procedures lie at the heart of the closeout phase of construction projects under contract law. However, due to its complexity involving multiple issues, potentially unfulfilled contractual obligations, performance claims and counter-claims, combined with consequently deteriorating stakeholder relationships, the management of closeouts is fraught with difficulties leading to suboptimal outcomes. This is particularly true where general contractor (GC) organizations do not have a claims management office (CMO) dedicated to improving such suboptimal clean-up outcomes. Thus, this study aims to develop a model by which CMOs’ may effectively manage the clean-up phase in an environment of closeout claims.Design/methodology/approachX-inefficiency theory was utilized as the theoretical lens guiding this study. The theory helps identify closeout strategies implemented by a GC, which manages completion claims through a CMO. Data were received and analyzed from a large GC, which served as the firm case study. In this case, managing the closeout completion claims was the main function of the CMO.FindingsThe average delay of closeout completion was four times greater than construction phase delays. The GC results highlighted the “economic destruction tsunami of projects,” as a root cause for these completion delays. Wrap-up activities under contract law are identified, including within the domains of statements of completion, project handover and debt settlement. Behavior strategies are also defined, including relational and contractual approaches. Moreover, a process for improving closeout claim performance is described, comprising project closeout identification, rational intra-firm behavior, closeout completion and program closeout practice.Originality/valueFindings from this work can significantly contribute in X-inefficiency theory in relation to how a decrease of X-inefficiency will lead to better closeout claim performance. It also offers practical insights into how best to minimize delayed closeout completion while providing valuable lessons for stakeholders in complex infrastructure projects. Further, a model is developed that may be utilized by owners, consultancies, designers and other contractor organizations in an effort to improve closeout claim performance.

Near-Real-Time Tracer Data Optimizes Well Cleanups in the Nova Field

_ This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper SPE 214351, “Near-Real-Time Tracer Data From the Onsite Tracer Analysis in the Nova Field,” by Alireza Roostaei, SPE, Ehsan Nikjoo, SPE, and Ali Nadali, SPE, Resman, et al. The paper has not been peer reviewed. _ This paper describes how near-real-time tracer data from an onsite tracer analysis enabled the operator to interactively optimize two well cleanups in the Nova field. The tracers provided key information on the cleanup progress in different zones, which enabled the operator to make informed and fast decisions to maximize well-cleanup efficiency while minimizing rig time and cost. Introduction The Nova field is in the northeastern North Sea. Reservoir sands are at depths of 2500–2800 m, with a pressure of approximately 290 bar and temperatures up to 110°C. The field will be operated with six wells—three oil producers and three water injectors—with an injector/producer pair in each of the main fault compartments. The authors, in the complete paper, show the value of inflow tracer data during the cleanup phase of two producers (X-3H and X-4 AHT2) in the field. Well-Cleanup Challenges and Monitoring Requirements The main challenge is to ensure that the well is sufficiently cleaned up at the zonal level while rig time and cost is minimized. Therefore, a monitoring method is required that can provide real-time data of cleanup progress in different zones. The data enables the operator to make informed decisions while the cleanup is ongoing, allowing optimization of well cleanup when needed. The risk-free and cost-effective inflow tracers with onsite analysis provide near-real-time data on cleanup efficiency in different zones. Because the Nova wells are equipped with inflow tracers, the operator used this data to understand the wells’ behavior and make real-time decisions to increase cleanup efficiency and zonal productivity. Equipment and Processes Inflow tracers are integrated in polymer rods that are stable in a wide range of well conditions. These inflow (in-well) tracers have been tested and designed in different hydrocarbon fluids and a broad temperature range (20–200°C). In the Nova field, unique oil and water tracers were deployed in the lower completion. These intelligent tracers remain dormant until they come in contact with their target fluids. Oil-based mud (OBM) was used as a lower completion fluid in the Nova oil wells; thus, the release of oil tracers began with contact with OBM. The polymer tracer rods are installed in the completion before running in hole; therefore, no downhole intervention is required. Each unique oil-tracer system consists of several polymer rods distributed evenly around the pipe in a carrier. The venting configuration of these systems is shown in Fig. 1. Once the tracers are released from the polymer rods, they will travel to surface with the fluid flow. At surface, samples are taken with different sampling frequencies depending on the monitoring objectives. The samples then are analyzed in a laboratory to identify and quantify tracers. The samples can be analyzed onsite or offsite.

The Entrainment of Task Allocation and Release Cycles in Open Source Software Development

In this study we identify a process of “entrainment” around open source software (OSS) development release cycles to capture patterns of self-organized task allocation among developers. We conducted an abductive, computationally intensive study of eight OSS projects, using relational event modeling to analyze 1,169,489 actions covering 93 major software releases. The process of entrainment that we identify involves three task allocation mechanisms: (1) developer-issue inertia, (2) developer contribution frequency, and (3) issue popularity. Our analysis demonstrates that these mechanisms and the phases of the release cycle entrain each other. Before a major release, developers engage in a concentrated mobilization phase, whereby they democratize development activity and increasingly allocate community contributions to the set of issues related to the release. After a major release, the extended cleanup phase garners a greater share of development work from recently highly active developers and dilutes the activity of these developers across a wider range of issues. Our theorizing suggests that major releases constitute important events around which OSS communities self-organize and we characterize how this occurs. Our research contributes to theorizing on organizing in OSS communities by explaining how self-organizing task allocation interacts with release cycles through the mechanism of entrainment. We also contribute to the literature on entrainment by showing how it may unfold in the context of online peer production communities such as OSS.

Modelling the recovery of resident shorebirds following a fox eradication program using citizen science data

Historically, the land-based threat to shorebird colonies on Phillip Island, Victoria, Australia, was fox predation. As a result, a fox eradication programme consisting of three phases: knock-down (i.e., 2006), clean-up (i.e., 2011), and post-eradication. In 2011 an effective knock-down was declared, signalling the beginning of the clean-up phase. The purpose of this research is to assess the recovery of six resident shorebird species on Phillip Island following fox removal. The statistical methodologies used are novel for assessing bird species population recovery following a successful predator eradication program. We used citizen science data from 2003 to 2017, extracted from the Atlas of Living Australia. The first analysis method used INLA modelling, which relied on a Negative Binomial distribution for bird counts to look for upward trends in shorebird populations during the fox eradication operation. The second method use changepoint analysis techniques to see whether successive phases of the eradication process were associated with changes in bird population numbers. Four of the six shorebird species investigated responded positively to reduced fox populations over the 15-year study, and all changepoint approaches consistently recognised the start of the clean-up phase, with less consistency identifying the start of the knock-down phase. Since 2006, the INLA models indicate a significant increase in the upward trend of shorebird populations for three of the six shorebird species investigated. Agreement across the four changepoint techniques indicates that changes in bird numbers were associated with the date of the eradication program's clean-up phase for all of these shorebird species. These results demonstrate some promise for these methods to monitor native species recovery during eradication programs.

Comparison of Extraction and Clean-up Methods Modified in Different Ways for the Determination of Pesticide Residues in Bees

As a result of the unconscious use of pesticides, honeybees are adversely affected, thus causing colony losses all over the world. In this research, different extraction and clean-up methods were compared on bee samples based on the QuEChERS method which is the most widely used pesticide analysis method in food. This research includes application studies for the multi residue method (MRM), which allows analysis of more than one pesticide. During the extraction phase, 7 different methods were compared, while the method with the most suitable repeatability and recovery values among these methods was taken to the clean-up phase. In the clean-up phase, 5 different clean-up methods were tried on the method which yielded the best values in extraction. In terms of average percentage recovery values, the 1stextraction method ranks first with 72 active substances between 70-120%, and the 3rd clean-up method with 92 active substances. Thus, while the number of active substances with suitable recovery values in the selected extraction method was 72, it increased to 92 with the continuation of the clean-up method, achieving a success rate of 92%. It is recommended to use this method in pesticide residue analyzes in bees with its outstanding features such as completing the analyzes in a short time, working easily with the infrastructure that can be found in all control laboratories, low analysis costs, ease of use, and reliability.

A validated UHPLC-MS/MS method for simultaneous quantification of some repurposed COVID-19 drugs in rat plasma: Application to a pharmacokinetic study

Since the emergence of Corona virus disease (COVID-19) in 2019, a number of medications have been developed and tried to combat the pandemic. In the present study, we develop a LC-MS/MS approach to detect and quantify certain COVID-19 candidate drugs in rat plasma, including Hydroxychloroquine, Favipiravir, Oseltamivir, and Remdesivir. The analytes were separated using Ultra High-Pressure Liquid Chromatography (UHPLC) over a 13-minute run on a C18 column. The extraction solvent for the (QuEChERS) quick, easy, cheap, effective, rugged and safe method was methanol, while the clean-up phase was primary secondary amine (PSA). Satisfactory recoveries were achieved for all compounds ranging from 82.39 to 105.87 %, with standard deviations smaller than 15.7. In terms of precision, accuracy, linearity, matrix effect, and stability, the method was validated according to US FDA criteria. The Limit of Detection (LOD) was determined to be between 0.11 and 10 ppb. The approach was further developed for a modest pharmacokinetic research in laboratory rats, and thus can be suitable for therapeutic drug monitoring in clinical cases under the same treatment.

Online Traffic Accident Spatial-Temporal Post-Impact Prediction Model on Highways Based on Spiking Neural Networks

Traffic accident management as an approach to improve public security and reduce economic losses has received public attention for a long time, among which traffic accidents post-impact prediction (TAPIP) is one of the most important procedures. However, existing systems and methodologies for TAPIP are insufficient for addressing the problem. The drawbacks include ignoring the recovery process after clearance and failing to make comprehensive prediction in both time and space domain. To this end, we build a 3-stage TAPIP model on highways, using the technology of spiking neural networks (SNNs) and convolutional neural networks (CNNs). By dividing the accident lifetime into two phases, i.e., clean-up phase and recovery phase, the model extracts characteristics in each phase and achieves prediction of spatial-temporal post-impact variables (e.g., clean-up time, recovery time, and accumulative queue length). The framework takes advantage of SNNs to efficiently capture accident spatial-temporal features and CNNs to precisely represent the traffic environment. Integrated with an adaptation and updating mechanism, the whole system works autonomously in an online manner that continues to self-improve during usage. By testing with a new dataset CASTA pertaining to California statewide traffic accidents on highways collected in four years, we prove that the proposed model achieves higher prediction accuracy than other methods (e.g., KNN, shockwave theory, and ANNs). This work is the introduction of SNNs in the traffic accident prediction domain and also a complete description of post-impact in the whole accident lifetime.

Critical review of the analytical methods for determining the mycotoxin patulin in food matrices

Abstract This manuscript is a critical review of the analytical methods reported in the existing literature for the determination of mycotoxin patulin at trace/ultra-trace levels in food matrices. The article starts focusing on what mycotoxins are, their “analytical history” (more than 21,000 articles published in Scopus database): each mycotoxin is specific for a given fungus and shows toxic effects, some even being carcinogenic. Most International regulations on mycotoxins are also reported, which pertain official controls in the food chain as well as the sampling methods and the maximum tolerable limits of mycotoxins. Then the manuscript is focused on patulin, a mycotoxin that is mainly produced by the fungal species Penicillium expansum. The main characteristics and properties of patulin are discussed, including its biosynthesis, especially on stored fruits infected by P. expansum and derived products, its toxicology, and some strategies aiming at preventing and/or reducing its presence. The description of the analytical procedure for patulin starts from sampling: the extraction and analytical methods reported are based on the official protocol of the Association of Official Analytical Chemists, which relies on the high-performance liquid chromatography-ultraviolet/diode array detector (HPLC-UV/DAD). Furthermore, an in-depth discussion of the most suitable analytical methods is reported. The first analytical step regards the analyte(s) extraction from the sample, followed by a clean-up phase, and by a final quantitative determination. This last section is divided into reference or confirmation methods, rapid screening and new methods and expected results, i.e., qualitative, quantitative, or semi-quantitative. Reference methods include TLC, GC, HPLC, and MS, whereas rapid methods include enzyme immunoassay tests, dipsticks, and lateral flow tests. Novel analytical methods include fluorescence, near infrared spectroscopy, capillary electrophoresis, and biosensors. Finally, the official method is compared with others present in the literature allowing a multi-target analysis, and its use in combination with other techniques of molecularly imprinted polymers is discussed.

A simulation optimization method for deep-sea vessel berth planning and feeder arrival scheduling at a container port

Vessels served by a container port can usually be classified into two types: deep-sea vessels and feeders. While the arrival times and service times of deep-sea vessels are known to the port operator when berth plans are being devised, the service times of feeders are usually uncertain due to lack of data interchange between the port operator and the feeder operators. The uncertainty of feeder service times can incur long waiting lines and severe port congestion if the service plans for deep-sea vessels and feeders are poorly devised. This paper studies the problem of how to allocate berths to deep-sea vessels and schedule arrivals of feeders for congestion mitigation at a container port where the number of feeders to be served is significantly larger than the number of deep-sea vessels, and where the service times of feeders are uncertain. We develop a stochastic optimization model that determines the berth plans of deep-sea vessels and arrival schedules of feeders, so as to minimize the departure delays of deep-sea vessels and schedule displacements of feeders. The model controls port congestion through restricting the expected queue length of feeders. We develop a three-phase simulation optimization method to solve this problem. Our method comprises a global phase, a local phase, and a clean-up phase, where the simulation budget is wisely allocated to the solutions explored in different phases so that a locally optimal solution can be identified with a reasonable amount of computation effort. We evaluate the performance of the simulation optimization method using test instances generated based on the operational data of a container port in Shanghai.

A LC-HRMS After QuEChERS Cleanup Method for the Rapid Determination of Dye Residues in Fish Products

The reliability of a rapid LC-HRMS method was studied in order to find a sensitive and accurate, simple, cheap, and rapid method for screening and quantitative determination of malachite green (MG), leucomalachite green (LMG), brilliant green (BG), crystal violet (CV), and leucocrystal violet (LCV) in fish muscle. All the analytes were extracted using a mixture of acetonitrile and citrate buffer, while the cleanup phase was carried out by Quick, Easy, Cheap, Effective, Rugged, and Safe (QuEChERS) method. All the data analyzed were acquired using both full MS and dd-MS2 modes. Good specificity, precision (relative standard deviation <11% for each sample tested), recovery (10–60%), decision limit (CCα between 0.55 and 0.62 μg kg−1), detection capabilities (CCβ between 0.65 and 0.78 μg kg−1), and ruggedness were achieved for the reliability of the method. Satisfactory results were obtained during the linearity test in the range of 0.10–2 ng mL−1 (r 2 > 0.999). Best recoveries were obtained by the QuEChERS cleanup method for all the analytes examined, presenting values between 70 and 104%. The application of 70,000 FWHM mass resolution and narrow mass windows significantly improved the selectivity of the method, leading to simultaneous screening and quantification of dye residues in comparison to other methods proposed in literature. The optimized method proposed in this work enables a simple and fast preparation; it offers exceptional sensitivity and selectivity and maximizes efficiency and reproducibility with a low consumption of reagents. Finally, the present method was successfully employed to detect dye residues in 73 fish samples, as provided for the national residue control plan.

The fate of fracturing water: A field and simulation study

Hydraulic fracturing of multi-lateral horizontal wells for shale gas production usually requires a great amount of water. Field data indicate that only a small fraction of the injected water can be recovered during the clean-up phase. Especially, when shale oil and gas wells undergo month-long shut-in periods after multi-stage fracturing processes. Field data also indicate that in some wells, such shut-in episodes surprisingly increase the oil and gas flow rate. However, the fate of non-recovered water in the reservoir and the reasons behind increased early-time oil and gas production after a long shut-in period are poorly understood.In this paper, we first interpret the flowback data of a 18-well pad completed in the Horn River Basin. Then, we use a numerical simulator to investigate the parameters controlling water and gas production during the flowback process. In the simulation model, the shale reservoir is represented by a fracture–matrix model, where the fractures form a continuum of interconnected network. The simulation results show that the counter-current imbibition of fracturing water during the shut-in period can result in a significant gas build-up in the fractures and therefore increases early-time gas production rate. It was also concluded that early-time water and gas production depends on reservoir properties such as capillary pressure and complexity of created fracture network and operational parameters such as shut-in time. The gas production rates from reservoirs with higher capillary pressure is higher at the beginning of flowback process but the production rate falls later. The complexity of fracture network created during hydraulic fracturing process has a great effect on load recovery and gas production. As the complexity increases, the gas production rate increases and load recovery decreases due to higher contact surface created between fractures and shale matrices. Further, field data and simulation results show that extended shut-in period increases early-time gas production but it decreases load recovery and late-time gas production.

Estimating reliable gas rate with transient-temperature modeling for interpreting early-time cleanup data during transient testing

Abstract In drillstem testing (DST), analyses of transient data are generally restricted to the post-cleanup period because rates often go unmonitored at early times during the cleanup phase, unless aided by multiphase flow metering. The value of early-time production data monitoring may be overlooked for two reasons: first, transients may be difficult to interpret because of two-phase flow in the formation; second, two-phase flow metering becomes a requirement. The objective of this study is two-fold: to estimate rate from multipoint-temperature sensor (MTS) data available for downhole telemetry with a rigorous transient analytical model, and to show the possible use of the computed rates to perform transient analysis for both the pre- and post-cleanup periods. Comparing and contrasting permeability estimates from the two periods provides guidance on the suitability of this approach. To that end, this study compares and contrasts rate computation with analytical methods. The new methods entail transient-temperature modeling with and without superposition effects. Two field examples strengthened the new rate-computation methods introduced here, and simulated examples probed the possibility of extracting meaningful information from the cleanup data.

An all-digital semi-blind clock and data recovery system

This paper presents a digitally intensive semi-blind clock and data recovery (SBCDR) system. The paper covers the theory, analysis, and system level simulation of this SBCDR. The proposed CDR is tailored to target the optical network standard OC-192. The SBCDR can provide the required jitter tolerance (JTo), and still provide enough jitter filtering to achieve the jitter transfer (JTr) requirements. Also, the recovered clock achieves a low jitter generation (JG) of 0.01 UIrms and 0.0064 UIrms for both the wide-band and high-band jitter filters defined by the standard. The proposed SBCDR provides two advantages over typical SBCDRs and PLL-based CRDs that target OC-192. First, the digitally intensive nature provides a scalable and process tolerant design. Second, the architecture provides a CDR that can pass all three jitter performance metrics, without the aid of an external clean-up phase locked loop (PLL) or a high performance clock multiplication unit (CMU) typically required by OC-192 transceivers. By utilizing a circular representation for the phase calculation in the over-sampling clock and data recovery (OSCDR), extensive pipe-lining in the implementation and higher data rate tolerance can be achieved. The simulation results of the proposed SBCRD agree closely with theoretical results.

Embedded purification for electron beam induced Pt deposition using MeCpPtMe3

Two different room-temperature processes for the electron beam induced deposition of high purity platinum (Pt), using the standard MeCpPtMe3 precursor and oxygen for purification, have been investigated. The first process is a sequential method, which uses two independent gas injector systems (GIS) in order to perform a standard Pt deposition, followed by an e-beam post-irradiation under oxygen flux. The second process is a parallel, single-step process that includes a simultaneous flow of both precursor and oxygen, using an add-on device that can be mounted on the standard GIS needle. Both processes are effective in producing high purity Pt depositions close to 100 at%. The first method requires a high current and irradiation dose in the clean-up phase, and provides Pt structures with small voids, a maximum thickness of around 100 nm and resistivity of 88 ± 10 μΩ cm. The second method requires a high oxygen/precursor flux ratio and produces void-free structures with resistivity of 60 ± 5 μΩ cm, only six times the bulk value for Pt. The second method is easier to use and produces a void-free deposition of high purity Pt.

Determination of Aflatoxin M1 in Milk Powder by Ultrasonic-Assisted Extraction and Dispersive Solid-Phase Clean-up.

This work describes the application of ultrasound-assisted dispersive solid-phase extraction (UA-DSPE) as a sample preparation approach for aflatoxin M1 (AFM1) and also its subsequent determination by HPLC-fluorescence detection. A Box-Behnken design in combination with response surface methodology was implemented to determine the variables affecting the extraction procedure. The effects of different variables, including type and quantity of clean-up phase, ultrasonication time, ultrasonication temperature, nature and volume of the leaching solvent, were investigated in the optimization study. Primary secondary amine (PSA) and acetonitrile were selected as the clean-up phase and the leaching solvent, respectively. The obtained optimized values were 30 mg of PSA, 10 min ultrasonication time, 32°C ultrasonication temperature and 10 mL of acetonitrile. Under the optimal conditions, the limit of detection and limit of quantification were 0.0012 and 0.0045 µg kg(-1), respectively. The recoveries of the UA-DSPE procedure ranged from 80 to 92%, with relative standard deviations lower than 10% in all cases. Eventually, this method was successfully applied to the extraction of AFM1 in milk powder samples.

Determination of aflatoxins in rice samples by ultrasound-assisted matrix solid-phase dispersion.

This work describes the application of ultrasound-assisted matrix solid-phase dispersion as an extraction and sample preparation approach for aflatoxins (B1, B2, G1 and G2) and subsequent determination of them by high-performance liquid chromatography-fluorescence detection. A Box-Behnken design in combination with response surface methodology was used to determine the affecting parameters on the extraction procedure. The influence of different variables including type of dispersing phase, sample-to-dispersing phase ratio, type and quantity of clean-up phase, ultrasonication time, ultrasonication temperature, nature and volume of the elution solvent was investigated in the optimization study. C18, primary-secondary amine (PSA) and acetonitrile were selected as dispersing phase, clean-up phase and elution solvent, respectively. The obtained optimized values were sample-to-dispersing phase ratio of 1 : 1, 60 mg of PSA, 11 min ultrasonication time, 30°C ultrasonication temperature and 4 mL acetonitrile. Under the optimal conditions, the limits of detection were ranged from 0.09 to 0.14 ng g(-1) and the precisions [relative standard deviation (RSD%)] were <8.6%. The recoveries of the matrix solid-phase dispersion process ranged from 78 to 83% with RSD <10% in all cases. Finally, this method was successfully applied to the extraction of trace amounts of aflatoxins in rice samples.

Feeder-free reprogramming of human fibroblasts with messenger RNA.

This unit describes a feeder-free protocol for deriving induced pluripotent stem cells (iPSCs) from human fibroblasts by transfection of synthetic mRNA. The reprogramming of somatic cells requires transient expression of a set of transcription factors that collectively activate an endogenous gene regulatory network specifying the pluripotent phenotype. The necessary ectopic factor expression was first effected using retroviruses; however, as viral integration into the genome is problematic for cell therapy applications, the use of footprint-free vectors such as mRNA is increasingly preferred. Strong points of the mRNA approach include high efficiency, rapid kinetics, and obviation of a clean-up phase to purge the vector. Still, the method is relatively laborious and has, up to now, involved the use of feeder cells, which brings drawbacks including poor applicability to clinically oriented iPSC derivation. Using the methods described here, mRNA reprogramming can be performed without feeders at much-reduced labor and material costs relative to established protocols.

Multivariate optimisation of an ultrasound assisted-matrix solid-phase dispersion method combined with LC-fluorescence detection for simultaneous extraction and determination of aflatoxins in pistachio nut samples

This paper describes the application of ultrasound-assisted matrix solid-phase dispersion as an extraction and clean-up procedure for aflatoxins (B1, B2, G1 and G2) and subsequent determination by LC-fluorescence detection. A Box–Behnken design was used to determine the parameters influencing the extraction procedure through response surface methodology and experimental design. The influence of different variables including type of dispersing phase, sample-to-dispersing phase ratio, type and quantity of clean-up phase, ultrasonication time, ultrasonication temperature, nature and volume of the elution solvent were investigated in the optimisation study. C18, graphitic carbon black and acetonitrile were selected as dispersing phase, clean-up phase and elution solvent, respectively. The optimised values were sample-to-dispersing phase ratio of 1:1, 50 mg of graphitic carbon black, 11 min ultrasonication time, 30°C ultrasonication temperature and 3 ml acetonitrile. Under the optimal conditions the limits of detection (LODs) were ranged from 0.04–0.11 µg kg−1 and the relative standard deviations (RSDs) of the extraction method were less than 8.6%. The recoveries of the matrix solid-phase dispersion process ranged from 74% to 78% with relative standard deviation lower than 9% in all cases. Finally, the matrix solid-phase dispersion was successfully applied to extraction of trace amounts of aflatoxins in pistachio samples.

Determination of paraquat and diquat in drinking water and environmental water by high performance liquid chromatography coupled with on-line clean-up and solid phase extraction

An on-line solid phase extraction (SPE) system was used to eliminate the interferences sufficiently and fulfill the simple and sensitive determination of diquat and paraquat in tap and pond water. This on-line SPE system used two SPE cartridges. One was an Acclaim Mixed-Mode WAX-1 cartridge for the elimination of anionic interferences; the other one was an Acclaim Mixed-Mode WCX-1 cartridge for the enrichment of diquat and paraquat and the elimination of co-enriched cationic interferences. The baseline separation of diquat and paraquat was achieved on an Acclaim Trinity P1 column. A dual-gradient high performance liquid chromatographic (HPLC) system provided an efficient platform to fulfill the on-line SPE and separation, and the system operated under automatic control of chromatography data system software. The complete analysis only required 16 min, and the detection limits of the method were 0.12 microg/L for diquat and 0.10 microg/L for paraquat. The method is simple, rapid and sensitive, and can be applied to the determination of diquat and paraquat in drinking water and environmental water.

An Adaptive Hyperbox Algorithm for High-Dimensional Discrete Optimization via Simulation Problems

We propose an adaptive hyperbox algorithm (AHA), which is an instance of a locally convergent, random search algorithm for solving discrete optimization via simulation problems. Compared to the COMPASS algorithm, AHA is more efficient in high-dimensional problems. By analyzing models of the behavior of COMPASS and AHA, we show why COMPASS slows down significantly as dimension increases, whereas AHA is less affected. Both AHA and COMPASS can be used as the local search algorithm within the Industrial Strength COMPASS framework, which consists of a global search phase, a local search phase, and a final cleanup phase. We compare the performance of AHA to COMPASS within the framework of Industrial Strength COMPASS and as stand-alone algorithms. Numerical experiments demonstrate that AHA scales up well in high-dimensional problems and has similar performance to COMPASS in low-dimensional problems.