bluuebunny/crossref_metadata_2025 huggingface dataset:
Interactions between mosses (Bryophyta) and fungi
Authors: Davey Marie L. , Currah Randolph S.
Published: January 2007

A taxonomically diverse suite of fungi interacts with bryophytes as pathogens, parasites, saprobes, and commensals. Necrotrophic pathogens such as Tephrocybe palustris (Peck) Donk and Nectria mnii Döbbeler form patches of moribund gametophytes in otherwise healthy mats of mosses. These pathogens exhibit different methods of host cell disruption; N. mnii appears to displace the host cell protoplast with intracellular hyphae, while T. palustris causes host protoplast degeneration. Host responses to infection by bryopathogens are also variable. Host–pathogen relationships can be highly evolved, as in Bryophytomyces sphagni (Navashin) Cif., in which fungal propagules replace the bryophyte spores, and exploit the explosive dispersal mechanisms of the Sphagnum host. Bryophilous parasites tend to exhibit high tissue or cellular specificity with varying host specificity. For example, Octospora similis (Kirchstein) Benkert infects the rhizoids of species of Bryum, and Discinella schimperi (Navashin) Redhead specifically colonizes the mucilage producing cells of stems of Sphagnum squarrosum Crome. Eocronartium muscicola (Pers.) Fitzp. demonstrates a highly evolved host–parasite relationship in which the basidiocarp displaces the sporophyte and is fed directly by the gametophyte through specialized transfer tissues. Fungi such as Oidiodendron maius Barron are capable of decomposing moss cell walls that are generally resistant to decomposition because of their polyphenolic component. Mycorrhizal fungi, including Glomus, Suillus, and Endogone, have not been observed to form functional, nutrient-exchanging mycorrhizal interfaces with bryophytes, rather, they function as saprobes on moribund and senescent gametophytes. Finally, endophytic fungi may provide bryophyte hosts with greater tolerance to extreme pH or promote vegetative growth. In vivo observation of bryophyte–fungus interactions has provided insight into the types of interactions that occur; however to further understand the physiology, anatomy, and etiology of these interactions, it is necessary to culture bryophilous fungi in vitro and create artificial axenic systems for study.
The tonalite–trondhjemite–granodiorite (TTG) to granodiorite–granite (GG) transition in the late Archean plutonic rocks of the central Wyoming Province
Authors: Frost Carol D , Frost B Ronald , Kirkwood Robert , Chamberlain Kevin R
Published: January 2007

The 2.95–2.82 Ga quartzofeldspathic gneisses and granitoids in the Bighorn, western Owl Creek, and northeastern Wind River uplifts in the central Wyoming Province include low-K tonalite–trondhjemite–granodiorite (TTG) and high-K granodiorite–granite (GG) rocks. Both types of granitoids were intruded contemporaneously, although TTGs are more abundant in the older gneisses. The TTG suite consists of calcic to marginally calc-alkalic rocks that straddle the boundaries between metaluminous and peraluminous and between ferroan and magnesian compositions. Rare-earth element (REE) patterns of these rocks may be highly fractionated with low heavy rare-earth element (HREE) contents and modest to absent Eu anomalies but may also be less strongly HREE depleted. These rocks do not represent first-generation continental crust: most have unradiogenic Nd and radiogenic 207Pb/204Pb isotopic compositions that require the incorporation of isotopically evolved sources. The GG suite has compositions that are transitional between Archean TTG and modern, continental margin calc-alkalic rocks. The GG suite is characterized by higher alkali contents relative to CaO than the TTG suite and higher K/Na ratios but exhibits a similar range in REE patterns. The Nd, Sr, and Pb isotopic compositions of the GG suite are slightly less variable but lie within the range of those of the TTG suite. We interpret them as having a source similar to that of the TTG, perhaps forming by partial melting of preexisting TTG. The shift from TTG-dominated to GG-dominated continental crust was a gradual transition that took place over several hundred million years. Clearly subduction-related calc-alkalic magmatism is not recognized in the Wyoming Province prior to 2.67 Ga.
Patterns of diel vertical migration of zooplankton in acoustic Doppler velocity and backscatter data on the Newfoundland Shelf
Authors: Record Nicholas R , Young Brad de
Published: January 2007

Backscatter data from moored acoustic Doppler current profilers (ADCPs) are analysed to quantify the diel vertical migration patterns of zooplankton on the Newfoundland Shelf, Canada. Data from 11 moorings provide long time series (~100 days each) for in-depth statistical analysis. For one deployment, dry weight measurements of zooplankton are used to calibrate the acoustic backscatter. Quantification methods are developed and applied to the backscatter and vertical velocity time series to determine the characteristics of the observed diel migration. We show that the migration responds to changes in light intensity and water column temperature structure. We have sufficient spatial data to show high correlation of migration characteristics over spatial scales of up to tens of kilometres.
Physiological effects of simultaneous, abrupt seawater entry and sea lice (Lepeophtheirus salmonis) infestation of wild, sea-run brown trout (Salmo trutta) smolts
Authors: Wells Alan , Grierson Christal E , MacKenzie Monique , Russon Iain J , Reinardy Helena , Middlemiss Claire , Bjørn Pål A , Finstad Bengt , Bonga Sjoerd E. Wendelaar , Todd Christopher D , Hazon Neil
Published: January 2007

For wild, sea-run brown trout (Salmo trutta) smolts, the physiological consequences of abrupt transfer to seawater and simultaneous challenge with copepodid larvae of the sea louse, Lepeophtheirus salmonis (Krøyer, 1837), were investigated in the laboratory. Analysis of osmoregulatory, metabolic, and stress markers allowed the derivation of a sublethal threshold burden of L. salmonis, above which the host suffers major physiological stress. Noticeable lice effects, consistent across all measured markers, were not observed until L. salmonis developed to the mobile preadult and adult stages. Preadult L. salmonis caused significant increases in plasma chloride, osmolality, glucose, lactate, and cortisol and a significant reduction in haematocrit. Piecewise linear statistical approaches allowed the determination of abrupt changes in these physiological markers, attributable to the intensity of L. salmonis infestation on individual fish, and identification of overall threshold lice burdens. Thirteen mobile lice·fish–1(weight range 19–70 g) was a consistent breakpoint across several physiological measures. This information will provide a valuable, objectively derived tool to aid in the formulation of effective wild fisheries management policy concerning S. trutta conservation.
Steady-state lines of sand–silt mixtures
Authors: Yang S L , Sandven R , Grande L
Published: January 2007

The steady-state lines (SSLs) for sand–silt mixtures with various fines contents (0%, 5%, 10%, 15%, 20%, 30%, 50%, 70%, and 94%) were studied. It was indicated that the location of the SSL in the e–p′ space is different for each mixture, but the SSLs are parallel. In the e – ln p′ plot, the SSLs are similar for the mixtures with a fines content of less than the transitional fines content (TFC) when tested under drained and undrained conditions and the intergranular and interfine void ratios are used. The data diverge when the fines contents are equal to or greater than the TFC, even though the interfine void ratios are used. The results of the tests conducted under drained and undrained conditions produced a unique SSL in the p′–q space for each material. Different SSLs in the p′–q space were observed for the studied materials, and the friction angle at steady state varied in the range of 37.3°–42.2°. The study showed that the SSLs can be represented by one line in tests under drained conditions if the fines contents are less (0%–30%) than the TFC and the corrected intergranular void ratios are used. The lines can also be represented by one line for sand–silt mixtures with high fines contents (50%–94%) if the corrected interfine void ratios are used instead of void ratios. Key words: steady-state line, sand–silt mixtures, transitional fines content, drained and undrained triaxial tests.
CALCULATION OF THE Bc LEPTONIC DECAY CONSTANT USING THE SHIFTED N-EXPANSION METHOD
Authors: IKHDAIR SAMEER M. , SEVER RAMAZAN
Published: January 2007

We give a review and present a comprehensive calculation for the leptonic constant fBc of the low-lying pseudoscalar and vector states of Bc-meson in the framework of static and QCD-motivated nonrelativistic potential models taking into account the one-loop and two-loop QCD corrections in the short distance coefficient that governs the leptonic constant of Bc quarkonium system. Further, we use the scaling relation to predict the leptonic constant of the nS-states of the [Formula: see text] system. Our results are compared with other models to gauge the reliability of the predictions and point out differences.
ELECTRIC CHARGE QUANTIZATION IN SU(3)C ⊗ SU(3)L ⊗ U(1)X MODELS
Authors: DONG PHUNG VAN , LONG HOANG NGOC
Published: January 2007

Basing on the general photon eigenstate and the anomaly cancellation, we have naturally explained the electric charge quantization in two models based on the SU (3)C ⊗ SU (3)L ⊗ U (1)X gauge group, namely in the minimal model and in the model with right-handed neutrinos. In addition, we have shown that the electric charges of the proton and of the electron are opposite; and the same happens with the neutron and the neutrino. We argue that the electric charge quantization in these models is closely related with the generation number problem. In fact, both problems are properly solved as the direct consequences of the fermion content under the anomaly free conditions.
SIZE- AND COHERENCE-DEPENDENT THERMODYNAMIC PROPERTIES OF METALLIC NANOWIRES AND NANOFILMS
Authors: QI W. H.
Published: January 2007

A model is developed to account for the size- and coherence-dependent cohesive energy, melting temperature, melting enthalpy, vacancy formation energy and vacancy concentration of nanowires and nanofilms. It is found that the variation direction (increasing or decreasing) of the thermodynamic properties is determined by the coherent interface, and the quantity of variation depends on the crystal size. The calculated results on Pb nanowires and nanofilms are consistent with the available experimental values.
AN EXACT ANALYTIC APPROACH TO 3D PET IMAGE RECONSTRUCTION
Authors: KAO CHIEN-MIN , ZOU YU , CHO SEUNGRYONG , PAN XIAOCHUAN
Published: January 2007

We investigate the development of a new analytic approach for 3D PET reconstruction by extension of the chord-based approach for X-ray cone-beam tomography (XCBT). The extension is made possible by recognizing a connection that allows one to reformat 3D PET data into effective cone-beam data so that the chord-based approach can be applied. An important advantage of the new approach is that it can work with general PET system geometries, not limited to the conventional circular geometry. In this paper, we consider a rectangular PET system consisting of four flat-panel detectors. We derive exact analytic reconstruction algorithms for this system and evaluate their performances in numerical studies. Our preliminary results indicate that the derived algorithms can yield accurate reconstructions when applied to noiseless PET data that are generated by assuming the ideal projection model. The algorithms are also observed to respond reasonably well to data noise. Currently, our algorithms do not utilize the entire 3D PET data. Potential modifications to the algorithms for enabling the inclusion of the entire 3D PET data for reconstruction, as well as the theoretical significances and potential practical advantages of this new analytic reconstruction approach, are discussed.
FAST ANALYTICAL RECONSTRUCTION OF GATED CARDIAC SPECT WITH NON-UNIFORM ATTENUATION COMPENSATION
Authors: FAN YI , LU HONGBING , HAO CHONGYANG , LIANG ZHENGRONG , ZHOU ZHIMING
Published: January 2007

Conventionally, the inverse problem of gated cardiac SPECT is solved by reconstructing the images frame-by-frame, ignoring the inter-frame correlation along the time dimension. To compensate for the non-uniform attenuation for quantitative cardiac imaging, iterative image reconstruction has been a choice which could utilize a priori constraint on the inter-frame correlation for a penalized maximum likelihood (ML) solution. However, iterative image reconstruction in the 4D space involves intensive computations. In this paper, an efficient method for 4D gated SPECT reconstruction is developed based on Karhune-Loève (KL) transform and Novikov's inverse formula. The temporal KL transform is first applied on the data sequence to de-correlate the inter-frame correlation and then the 3D principal components in the KL domain are reconstructed frame-by-frame using Novikov's inverse formula with non-uniform attenuation compensation. Finally an inverse KL transform is performed to obtain quantitatively-reconstructed 4D images in the original space. With the proposed method, 4D reconstruction can be achieved at a reasonable computational cost. The results from computer simulations are very encouraging as compared to conventional frame-by-frame filtered back-projection and iterative ordered-subsets ML reconstructions. By discarding high-order KL components for further noise reduction, the computation time could be further reduced.
Mining with rarity
Authors: Weiss Gary M.
Published: January 2007

Rare objects are often of great interest and great value. Until recently, however, rarity has not received much attention in the context of data mining. Now, as increasingly complex real-world problems are addressed, rarity, and the related problem of imbalanced data, are taking center stage. This article discusses the role that rare classes and rare cases play in data mining. The problems that can result from these two forms of rarity are described in detail, as are methods for addressing these problems. These descriptions utilize examples from existing research. So that this article provides a good survey of the literature on rarity in data mining. This article also demonstrates that rare classes and rare cases are very similar phenomena---both forms of rarity are shown to cause similar problems during data mining and benefit from the same remediation methods.
A study of the behavior of several methods for balancing machine learning training data
Authors: Batista Gustavo E. A. P. A. , Prati Ronaldo C. , Monard Maria Carolina
Published: January 2007

There are several aspects that might influence the performance achieved by existing learning systems. It has been reported that one of these aspects is related to class imbalance in which examples in training data belonging to one class heavily outnumber the examples in the other class. In this situation, which is found in real world data describing an infrequent but important event, the learning system may have difficulties to learn the concept related to the minority class. In this work we perform a broad experimental evaluation involving ten methods, three of them proposed by the authors, to deal with the class imbalance problem in thirteen UCI data sets. Our experiments provide evidence that class imbalance does not systematically hinder the performance of learning systems. In fact, the problem seems to be related to learning with too few minority class examples in the presence of other complicating factors, such as class overlapping. Two of our proposed methods deal with these conditions directly, allying a known over-sampling method with data cleaning methods in order to produce better-defined class clusters. Our comparative experiments show that, in general, over-sampling methods provide more accurate results than under-sampling methods considering the area under the ROC curve (AUC). This result seems to contradict results previously published in the literature. Two of our proposed methods, Smote + Tomek and Smote + ENN, presented very good results for data sets with a small number of positive examples. Moreover, Random over-sampling, a very simple over-sampling method, is very competitive to more complex over-sampling methods. Since the over-sampling methods provided very good performance results, we also measured the syntactic complexity of the decision trees induced from over-sampled data. Our results show that these trees are usually more complex then the ones induced from original data. Random over-sampling usually produced the smallest increase in the mean number of induced rules and Smote + ENN the smallest increase in the mean number of conditions per rule, when compared among the investigated over-sampling methods.
Learning from imbalanced data sets with boosting and data generation
Authors: Guo Hongyu , Viktor Herna L.
Published: January 2007

Learning from imbalanced data sets, where the number of examples of one (majority) class is much higher than the others, presents an important challenge to the machine learning community. Traditional machine learning algorithms may be biased towards the majority class, thus producing poor predictive accuracy over the minority class. In this paper, we describe a new approach that combines boosting, an ensemble-based learning algorithm, with data generation to improve the predictive power of classifiers against imbalanced data sets consisting of two classes. In the DataBoost-IM method, hard examples from both the majority and minority classes are identified during execution of the boosting algorithm. Subsequently, the hard examples are used to separately generate synthetic examples for the majority and minority classes. The synthetic data are then added to the original training set, and the class distribution and the total weights of the different classes in the new training set are rebalanced. The DataBoost-IM method was evaluated, in terms of the
F-measures, G-mean
and
overall accuracy
, against seventeen highly and moderately imbalanced data sets using decision trees as base classifiers. Our results are promising and show that the DataBoost-IM method compares well in comparison with a base classifier, a standard benchmarking boosting algorithm and three advanced boosting-based algorithms for imbalanced data set. Results indicate that our approach does not sacrifice one class in favor of the other, but produces high predictions against both minority and majority classes.
Class imbalances versus small disjuncts
Authors: Jo Taeho , Japkowicz Nathalie
Published: January 2007

It is often assumed that class imbalances are responsible for significant losses of performance in standard classifiers. The purpose of this paper is to the question whether class imbalances are truly responsible for this degradation or whether it can be explained in some other way. Our experiments suggest that the problem is not directly caused by class imbalances, but rather, that class imbalances may yield small disjuncts which, in turn, will cause degradation. We argue that, in order to improve classifier performance, it may, then, be more useful to focus on the small disjuncts problem than it is to focus on the class imbalance problem. We experiment with a method that takes the small disjunct problem into consideration, and show that, indeed, it yields a performance superior to the performance obtained using standard or advanced solutions to the class imbalance problem.
Efficient distributed event driven simulations of multiple-loop networks
Authors: Lubachevsky B. D.
Published: January 2007

Simulating asynchronous multiple-loop networks is commonly considered a difficult task for parallel programming. This paper presents two examples of asynchronous multiple-loop networks: a stylized queuing system and an Ising model. The network topology in both cases is an
n
X
n
grid on a torus. A new distributed simulation algorithm is demonstrated on these two examples. The algorithm combines three elements: 1) the bounded lag restriction, 2) precomputed minimal propagation delays, and 3) the so-called opaque periods. Theoretical performance evaluation suggests that if
N
processing elements (PEs) execute the algorithm in parallel and the simulated system exhibits sufficient density of events, then, in average, processing one event would require
Ο
(log
N
) instructions of one PE. In practice, the algorithm has achieved substantial speed-ups: the speed-up is greater than 16 using 25 PEs on a shared memory MIMD bus computer, and greater than 1900 using 2
14
PEs on a SIMD computer.
A symptotic analysis of large heterogeneous queueing systems
Authors: Shenker S. , Weinrib A.
Published: January 2007

As a simple example of a large heterogeneous queueing system, we consider a single queue with many servers with differing service rates. In the limit of infinitely many servers, we identify a queue control policy that minimizes the average system delay. When there are only two possible server speeds, we can analyze the convergence of this policy to optimality. Based on this result, we propose policies for large but finite systems with a general distribution of server speeds.
Application level modeling of parallel machines
Authors: Kant K.
Published: January 2007

In this paper, we consider the application level performance modeling of parallel machines consisting of a large number of processing elements (PE's) connected in some regular structure such as mesh, tree, hypercube, etc. There are
K
problem types, each arriving according to a Poisson process, and each of which needs a PE substructure of some given size and topology. Thus several problems can run on the machine simultaneously. It is desired to characterize the performance of such a system under various types of allocation schemes.

We show that if the queueing is considered external to our model, it is possible to construct a Markovian model with local balance property. The time for which a substructure is held by a problem could be generally distributed. The model can be solved efficiently using standard techniques; however, because of rather complex structure of the state space, its direct enumeration is difficult to avoid. We also show how the size of the state space can be reduced when the set of allowed substructures is highly regular. We then show how queueing delays can be modeled approximately. Finally, we consider the solution of models involving shared resources such as global memory.
On hot-spot contention in interconnection networks
Authors: Patel N. M. , Harrison P. G.
Published: January 2007

A major component of a parallel machine is its interconnection network, which provides concurrent communication between the processing elements. It is common to use a multi-stage interconnection network (MIN) which is constructed using crossbar switches and introduces not only contention for destination addresses but also additional contention for internal switches. Both types of contention are increased when non-local communication across a MIN becomes concentrated on a certain destination address, for example when a frequently-accessed data structure is stored entirely in one element of a distributed memory. Such an address, often called a
hot-spot
, affects the blocking probability of paths to other destination addresses because of the shared internal switches. This paper describes an analytical model of hot-spot contention and quantifies its effect on the performance of a MIN with a circuit switching communication protocol. We obtain performance measures for a MIN in which partial paths are held during path building and one destination address is more frequently chosen by incoming traffic than other addresses.
A manufacturing capacity planning experiment through functional workload decomposition
Authors: Lee T. P.
Published: January 2007

In this paper, we describe an experiment to evaluate a distributed architecture via functional database workload decomposition. A workload in a circuit pack assembly environment was decomposed and mapped onto a frontend/backend distributed computer architecture. To evaluate this distributed architecture, an operational model for capacity planning was devised, and performance and cost-effectiveness measures were chosen. Model parameters were estimated through benchmark experiments in a distributed system consisting of various super-microcomputers connected by a CSMA/CD local area network with INGRES as the database management system.

The frontend/backend architecture consists of a backend data repository and analysis computer system and a few frontend computer systems dedicated for data collection and manufacturing process verification. Because of the significant software overhead in communication protocol and database processing, information exchange was batched between the backend and frontend systems to amortize such cost to improve overall system performance.

Results of the experiments were analyzed to gain quantitative insight on the feasibility of such decomposition and its mapping onto the proposed architecture. With sufficient batching, the proposed distributed architecture not only has more overall system capacity, but also is more cost-effective than the typical centralized architecture. The approach described is applicable in more general contexts. Advantages of such distributed systems include the relative robustness of the distributed architecture under single point failure mode and the ease of capacity growth by upgrading the computer systems and/or by increasing the number of frontend systems.
Comparison of dataflow control techniques in distributed data-intensive systems
Authors: Alexander W. , Copeland G.
Published: January 2007

In dataflow architectures, each dataflow node (i.e., operation) is typically executed on a single physical node. We are concerned with distributed data-intensive systems, in which each base (i.e., persistent) set of data has been declustered over many physical nodes to achieve load balancing. Because of large base set size, each operation is executed where the base set resides, and intermediate results are transferred between physical nodes. In such systems, each dataflow node is typically executed on many physical nodes. Furthermore, because computations are data-dependent, we cannot know until run time which subset of the physical nodes containing a particular base set will be involved in a given dataflow node. This uncertainty affects program loading, task activation and termination, and data transfer among the nodes
.

In this paper we focus on the problem of how a dataflow node in such an environment knows when it has received data from all the physical nodes from which it is ever going to receive. We call this the
dataflow control
problem. The interesting part of the problem is trying to achieve correctness efficiently. We propose three solutions to this problem, and compare them quantitatively by the metrics of total message traffic, message system throughput and data transfer response time
.
Characterising program behaviour with phases and transitions
Authors: Murphy J. M. , Bunt R. B.
Published: January 2007

A detailed quantitative study of program behaviour is described. Reference strings from a representative set of programs were decomposed into phases and transitions. Referencing behaviour is studied at both the macro level (program-wide) and the micro level (within the phases and transitions). Quantitative data, suitable for the parameterization of program behaviour models, is presented.
On the properties of approximate mean value analysis algorithms for queueing networks
Authors: Pattipati K. R. , Kostreva M. M.
Published: January 2007

This paper presents new formulations of the approximate mean value analysis (MVA) algorithms for the performance evaluation of closed product-form queueing networks. The key to the development of the algorithms is the derivation of vector nonlinear equations for the approximate network throughput. We solve this set of throughput equations using a nonlinear Gauss-Seidel type distributed algorithms, coupled with a quadratically convergent Newton's method for scalar nonlinear equations. The throughput equations have enabled us to: (a) derive bounds on the approximate throughput; (b) prove the existence, uniqueness, and convergence of the Schweitzer-Bard (S-B) approximation algorithm for a wide class of monotone, single class networks, (c) establish the existence of the S-B solution for multi-class, monotone networks, and (d) prove the asymptotic (i.e., as the number of customers of each class tends to ∞) uniqueness of the S-B throughput solution, and the asymptotic convergence of the various versions of the distributed algorithms in multi-class networks with single server and infinite server nodes. The asymptotic convergence is established using results from convex programming and convex duality theory. Extension of our algorithms to mixed networks is straighfoward. Only multi-class results are presented in this paper.
Comments on a linear paging model
Authors: Denning Peter J.
Published: January 2007

The linear approximation relating mean time between page transfers between levels of memory, as reported by Saltzer for Multics, is examined. It is tentatively concluded that this approximation is untenable for main memory, especially under working set policies; and that the linearity of the data for the drum reflects the behavior of the Multics scheduler for background jobs, not the behavior of programs.
Analysis of a time-sharing subsystem (A Preliminary Report)
Authors: Schwetman H. D.
Published: January 2007

The MESA subsystem provides a wide variety of services to remotely located users of the computing facilities of the Purdue University Computing Center. This paper presents the preliminary steps of an in-depth study into the behavior of MESA. The study uses a software data-gathering facility to analyze the usage and queueing aspects of this behavior and to provide values for parameters used by two models of the subsystem. These models, a network-of-queues model and a simulation model, are designed to project subsystem behavior in different operating environments. The paper includes a number of tables and figures which highlight the results, so far, of the study.
The analysis of storage constraints by a queueing network model with blocking
Authors: Reiser M. , Konheim A. G.
Published: January 2007

The finite capacity of storage has a significant effect on the performance of a contemporary computer system. Yet it is difficult to formulate this problem and analyze it by existing queueing network models.

We present an analysis of an open queueing model with two servers in series in which the second server has finite storage capacity.

This network is an exponential service system; the arrival of requests into the system is modeled by a Poisson process (of rate λ) and service times in each stage are exponentially distributed (with rates α and β respectively). Requests are served in each stage according to the order of their arrival. The principal characteristic of the service in this network is
blocking
; when M requests are queued or in service in the second stage, the server in the first stage is blocked and ceases to offer service. Service resumes in the first stage when the queue length in the second stage falls to M-1. Neuts [1] has studied two-stage blocking networks (without feedback) under more general statistical hypothesis than ours. Our goal is to provide an algorithmic solution which may be more accessible to engineers.
Statistical validation of a trace-driven simulator
Authors: Schatzoff M. , Tillman C. C.
Published: January 2007

A common problem encountered in computer system simulation is that of validating that the simulator can produce, with a reasonable degree of accuracy, the same information that can be obtained from the modelled system. This is basically a statistical problem because there are usually limitations with respect to the number of controlled tests which can be carried out, and assessment of the fidelity of the model is a function of the signal to noise ratio. That is, the magnitude of error which can be tolerated depends upon the size of the effect to be predicted.

In this paper, we describe by example how techniques of statistical design and analysis of experiments have been used to validate the modeling of the dispatching algorithm of a time sharing system. The examples are based on a detailed, trace-driven simulator of CP-67. They show that identical factorial experiments involving parameters of this algorithm, when carried out on both the simulator and on the actual system, produced statistically comparable effects.
Adaptive optimization of the performance of a virtual memory computer
Authors: Badel M. , Gelenbe E. , Leroudier J. , Potier D. , Lenfant J.
Published: January 2007

It is known that the regulation of the degree of multiprogramming is perhaps one of the most important factors determining the overall performance of a virtual memory computer. In this paper we present an approach which differs some what from the approaches usually taken to regulate the degree of multiprogramming, which are mainly derived from the working-set principles.

We design a controller which will regulate the system in order to optimize a given performance measure. The controller is applied to a system where the critical resource is primary memory, and we are only concerned with systems where ineffective regulation leads to the phenomenon known as thrashing due to extensive paging activity.

In the first section, the dynamics of the system we wish to regulate are investigated using an analytical model. The system consists of a set of terminals and of a resource loop (CPU, secondary memory device, file disk) shared by the users. Using classical assumptions about program behavior (e.g., life-time function), the throughput of the RL is obtained as a function of the degree of multiprogramming n (number of users sharing the resources at a given instant of time) and of the system parameters. This result provides a greater insight of the “plant” we wish to control. The mathematical results are validated and extended with data from simulation experiments using a more detailed model (overheads and non-exponential assumption).

In the next section, a criterion called “dilatation” based on the utilization of the different resources is defined. From the analytical and simulation results of the first section, it can be shown that there exists a value n
o
of the degree of multiprogramming which maximizes this criterion. The regulation of n to n
o
is achieved by controlling the access of the users to the RL. The value of n
o
is estimated in real-time through a continuous estimation of the two first moments of the criterion. Using these estimations, the decision of introducing or not a new user in the RL is taken whenever a user leaves a terminal or departs from the RL.

Extensive simulation experiments were conducted, where the implementation of the different functions of the controller have been thoroughly simulated. They have shown that the control scheme leaves to an improvement of the system performance in mean response time and resource utilization, and, overall, adapts in real-time the degree of multiprogramming to the characteristics of the users (the adaptation is performed in 4 sec. or so for a unit variation of the optimal degree of multiprogramming). A discussion of practical application of results ends the paper.
Batch computer scheduling
Authors: Kimbleton Stephen R.
Published: January 2007

Efficient scheduling of jobs for computer systems is a problem of continuing concern. The applicability of scheduling methodology described in the operations research literature is severely restricted by the dimensionality of job characteristics, the number of distinct resource types comprising a computer system, the non-deterministic nature of the system due to both interprocess interaction and contention, and the existence of a multitude of constraints effecting job initiation times, job completion times, and job interactions. In view of the large number of issues which must be considered in job scheduling, a heuristic approach seems appropriate. This paper describes an initial implementation of such an approach based upon a fast, analytically driven, performance prediction tool.
A comparison of software assurance methods
Authors: Fujii Marilyn S.
Published: January 2007

Several methods are currently employed by software developers to improve software quality. This paper explores the application of three of these methods: quality assurance, acceptance testing, and independent verification and validation. At first glance these methods appear to overlap, but a closer evaluation reveals that each has a distinct objective and an established set of procedures. The purpose of this paper is to clarify the role of each of these methods by examining their scope, organization, and implementation in the software development process.
A Requirements Tracing Tool
Authors: Pierce Robert A.
Published: January 2007

A software development aid termed the Requirements Tracing Tool is described. Though originally designed to facilitate requirements analysis and thus simplify system verification and validation, it has also proven useful as an aid for coping with changing software requirements and estimating their consequent cost and schedule impacts. This tool provides system analysts with a mechanism for automated construction, maintenance, and access to a requirements data base—an integrated file containing all types and levels of system requirements. This tool was used during the development of a large Navy undersea acoustic sensor system. It is presently being used to support the Cruise Missile Mission Planning Project. An outline version of this tool is under development.
Requirements language processing for the effective testing of real-time systems
Authors: Davis Alan M. , Rataj Walter J.
Published: January 2007

GTE Laboratories is currently developing a trio of software tools which automate the feature testing of real-time systems by generating test plans directly from requirements specifications. Use of the first of these tools, the Requirements Language Processor (RLP), guarantees that the requirements are complete, consistent, non-ambiguous, and non-redundant. It generates a mode] of an extended finite-state machine which is used by the second tool, the Test Plan Generator, to generate test plans which thoroughly test the software for conformity to the requirements. These test plans are supplied to the third tool, the Automatic Test Executor, for actual testing. The RLP is the subject of this paper.

The primary goal of the RLP is to provide the ability to specify the features of a target real-time system in a vocabulary familiar to an application-oriented individual and in a manner suitable for test plan generation. The RLP produces a document which can be easily understood by non-computer personnel. It is expected that this document will function as a key part of the “contract” between a real-time system supplier and a customer. This document must also serve as a springboard for the software designers during their development of the actual product.

In addition to the requirements document, the RLP also produces an augmented state transition table which describes a finite state machine whose external behavior is identical to the target real-time system as defined by the specified requirements.
Nassi-Shneiderman charts an alternative to flowcharts for design
Authors: Yoder Cornelia M. , Schrag Marilyn L.
Published: January 2007

In recent years structured programming has emerged as an advanced programming technology. During this time, many tools have been developed for facilitating the programmer's use of structured programming. One of these tools, the Structured Flowcharts developed by I. Nassi and B. Shneiderman in 1972, is proving its value in both the design phase and the coding phase of program development.

Several programming groups in System Products Division, Endicott, New York, have used the Nassi-Shneiderman charts as replacements for conventional flowcharts in structuring programs. The charts have been used extensively on some projects for structured walk-throughs, design reviews, and education.

This paper describes the Nassi-Shneiderman charts and provides explanations of their use in programming, in development process control, in walk-throughs, and in testing. It includes an analysis of the value of Nassi-Shneiderman charts compared to other design and documentation methods such as pseudo-code, HIPO charts, prose, and flowcharts, as well as the authors' experiences in using the Nassi-Shneiderman charts.

The paper is intended for a general data processing audience and although no special knowledge is required, familiarity with structured programming concepts would be helpful. The reader should gain insight into the use of Nassi-Shneiderman charts as part of the total development process.
IDBUG
Authors: Drasch Frederick J. , Bowen Richard A.
Published: January 2007

The construction of a reliable computer program requires, in part, a means of verification of its component parts prior to their integration into the overall system. The verification process may consist of building a test harness to exercise or exhaustively test a procedure. This technique is known as dynamic testing. In practice, the application of dynamic testing requires the coding of a special harness for each procedure. This consumes valuable programming time, as much as 50% of the total effort (FAIR78). It is also restrictive because the test harness cannot be easily modified to test aspects of a program which it was not originally designed to test.

We have built a facility called IDBUG that reduces the programming effort required to employ dynamic testing by automating the construction of the test harness. Additionally, it provides an interactive test environment which permits more flexible testing. This paper describes IDBUG and discusses our experience in its application to maintenance tasks in a commercial environment. Nyone of the ideas put forth here will be especially novel; dynamic testing as a software testing tool has been in use for some time. What we hope to do is illustrate the beneficial aspects of a particular application of dynamic testing. It is argued that testing should play a more limited role in assuring the reliability of software in light of techniques such as structured coding, top-down design, proof of correctness, etc. (McG075). While it is true that eventually the “art of computer programming” will become the “science of producing correct programs”, we believe that more emphasis must be placed on interim solutions to aid in the construction of reliable software. We present IDBUG as such a solution.
An application of graph theory to software test data selection
Authors: Stickney M. E.
Published: January 2007

Graph theory is playing an increasingly important role in the design, analysis, and testing of computer programs. It's importance is derived from the fact that flow of control and flow of data for any program can be expressed in terms of directed graphs. From the graph representing the flow of control, called the program graph, many others can be derived that either partially or completely preserve the program control structure. One derived graph known as a cyclomatic tree is of particular value in program testing. It is so named because the number of leaves of the tree is equal to the cyclomatic number of the program graph. A thorough treatment of cyclomatic numbers is provided in [3]. A program called the Complexity/Path Analyzer (CPA) has been developed that builds and utilizes a program cyclomatic tree to provide test planning information, automatically place software counters called probes as discussed in [9] and [10] in a program, and provide selected parameters such as program length and program graph cyclomatic number. The paper discusses the features and derivation of cyclomatic trees as well as their value and application to testing and test data generation.

A cyclomatic tree provides a test planner with information useful for planning program tests. In particular, it furnishes test data selection criteria for developing tests that are minimally thorough as defined by Huang in [9]. A test data selection criterion will be defined as minimally thorough if any complete test with respect to the criterion is at least minimally thorough. The term complete is used as defined by Goodenhough and Gerhart in [13]. A test is defined to be a non empty sequence of test cases. Each test case consists of an element selected from the input domain of the program being tested. The paper discusses the merits of one particular technique selected to achieve a minimally thorough test data selection criteria. Part of the technique is automated by the CPA program.
Software quality assurance tools
Authors: Fischer Kurt F.
Published: January 2007

The objective of software quality assurance (QA) is to assure sufficient planning, reporting, and control to affect the development of software products which meet their contractual requirements. To implement this objective, eight QA functions can be identified:

1. Initial quality planning

2. Development of software standards and procedures

3. Development of quality assurance tools

4. Conduct of audits and reviews

5. Inspection and surveillance of formal tests

6. Configuration verifications

7. Management of the discrepancy reporting system

8. Retention of QA records

The purpose of this paper is to document experiences gained in the use of selected QA tools that perform some of the above functions, to discuss lessons learned, and to suggest future needs.
The evolution of a Source Code Control System
Authors: Glasser Alan L.
Published: January 2007

The Source Code Control System (SCCS) is a system for controlling changes to files of text (typically, the source code and documentation of software systems). It is an integral part of a software development and maintenance system known as the Programmer's Workbench (PWB).

SCCS has itself undergone considerable change. There have been nine major versions of SCCS. This paper describes the facilities provided by SCCS, and the design changes that were made to SCCS in order to provide a useful and flexible environment in which to conduct the programming process.
A mini-computer based library control system
Authors: Josephs William H.
Published: January 2007

One of the major problems encountered in any large scale programming project is the control of the software. Invariably, such large programs are divided into many smaller elements since these are easier to code, test and document. However, such a division adds new complexity to the task of Configuration Management since the many source modules, data base elements, JCL (Job Control Language) and DATA files must be controlled with the goal of maximizing program integrity and minimizing the chances of procedural errors. Furthermore, whenever any program is released either for field test or for final production, an entire change control procedure must be implemented in order to trace, install, debug and verify fixes or extensions to the original program. These maintenance activities can account for up to 80 percent of the entire programming cost in a large, multi-year project. The library control program (SYSM) presented here was developed to aid in these processes. It has facilities for capturing all elements of a program (commonly called baselining), editing any element or group of elements that have been baselined to build an updated version of the program, adding and/or deleting elements of a program, and listing the current contents of a given element or elements. SYSM is written mainly in FORTRAN, and runs on a Hewlett-Packard HP-21MX computer with two tape drives, the vendor supplied RTE-II or RTE-III operating system, and at least 16K of user available core. It can be used to control code targeted for either the HP21MX itself, or, using the optional HP/LSI-11 link program, code targeted for a Digital Equipment Corp. LSI-11 system.