bluuebunny/crossref_metadata_2025 huggingface dataset:
Efficiencies of benthic and pelagic trophic pathways in a subalpine lake
Authors: Vander Zanden M Jake , Chandra Sudeep , Park Sang-Kyu , Vadeboncoeur Yvonne , Goldman Charles R
Published: January 2007

Although the study of lakes has traditionally focused on pelagic production pathways, recent stable isotope and diet evidence indicates that benthic algal production is an important contributor to fish production. This has led to the suggestion that energy may be more efficiently passed along benthic food chains relative to their pelagic counterparts. To test this idea, we combined stable isotope based assessments of energy flow pathways with estimates of pelagic- and benthic-based primary and secondary production in Castle Lake, California. Approximately 50% of whole-lake primary production and 30% of whole-lake secondary production occurred in benthic habitats. Stable carbon isotopes and dietary data indicated that fish were predominantly supported by benthic (63%) and terrestrial (24%) secondary production. Ecological efficiencies (algal production / invertebrate production) were low in Castle Lake (<3%), though zoobenthic production was more efficiently passed to fish than was zooplankton production. The larger size of benthic prey relative to pelagic prey may affect fish prey selection and foraging efficiency, resulting in differences in ecological efficiency between pelagic and benthic trophic pathways.
“Big” concerns with high latitude marine protected areas (MPAs): trends in connectivity and MPA size
Authors: Laurel Benjamin J , Bradbury Ian R
Published: January 2007

The success of marine protected areas (MPAs) as fisheries management tools in tropical latitudes has generated interest in their applicability and potential elsewhere. Here we suggest that dispersal and gene flow in marine fish populations (a primary biological consideration for marine reserve design) increases with latitude. For example, north temperate fish species at latitudes between 40° and 45° had about three times greater dispersal potential (planktonic larval duration (PLD), n = 96 species) and genetic homogeneity (FST, n = 100 species) than fish species near equatorial regions. Using the PLD and FST relationships, dispersal increases at a rate of ~8% per degree of latitude north or south of the equator. Therefore tropical MPAs should not serve as direct scalar templates in other regions, but rather should be used as a basis against which higher-latitude MPAs should be scaled. However, a review of 429 existing MPAs indicates that no such changes in reserve size have been implemented with respect to latitude. Fisheries managers must be prepared and willing to implement MPAs at large scales in high latitudes, either as single reserves or in a network, or else we lose the legitimacy of a new and promising management tool for conserving marine biodiversity in cold ocean regions.
Using zooplankton biomass size spectra to assess ecological change in a well-studied freshwater lake ecosystem: Oneida Lake, New York
Authors: Gamble Allison E , Lloyd Russ , Aiken John , Johannsson Ora E , Mills Edward L
Published: January 2007

We explored the sensitivity of three descriptors of zooplankton size spectra (slope, periodic, and Pareto II models) to environmental changes in Oneida Lake, New York, and then used documented environmental changes to model the responses of zooplankton biomass using a general linear model. Using multiple regressions, we identified significant ecological events in Oneida Lake that could affect zooplankton biomass before actual model testing and assessed the three size spectrum models based on their sensitivity to these known variables. The intercept of the slope (linear regression) model was responsive to changes, but the slope was not. The periodic (quadratic) model showed no sensitivity in detecting ecological change. The Pareto II model (probability distribution function) demonstrated the most sensitivity to all ecological variables but was complex to model and there was no direct relationship between its parameters and biological events. The general linear model regression approach proved relatively sensitive to environmental change and had the added benefit of providing a graphical means of biologically assessing differences between years. In general, zooplankton biomass size spectra were responsive to changes in conditions in the Oneida Lake environment, and we believe that size-based approaches have potential as a biotic index in freshwater lake ecosystems.
Mysid and fish zooplanktivory in Lake Ontario: quantification of direct and indirect effects
Authors: Gal Gideon , Rudstam Lars G , Mills Edward L , Lantry Jana R , Johannsson Ora E , Greene Charles H
Published: January 2007

Mysis relicta and planktivorous fish feed on zooplankton in Lake Ontario and form a trophic triangle that includes intraguild predation by fish on mysids. Thus, fish affect zooplankton both directly and indirectly. To evaluate the importance of alewife (Alosa pseudoharengus), rainbow smelt (Osmerus mordax), and mysids as zooplanktivores in Lake Ontario, we measured abundances and distributions, assessed diets, and computed mysid and fish consumption rates based on bioenergetics models. We further estimated indirect effects by comparing clearance rates given observed and potential mysid distributions. Estimated consumption rates varied widely with season and water depth and ranged between 2.6 × 10–3 and 1.3 g·m–2·day–1 for mysids and between 1.4 × 10–3 and 0.5 g·m–2·day–1 for fish, representing a daily removal of zooplankton of up to 10.2%·day–1 and 2.0%·day–1 by mysids and fish, respectively. Mysid planktivory exceeded fish planktivory in May and August, but fish planktivory dominated in October. Estimated mysid planktivory rates were 2- to 90-fold lower than the potential rate if mysids moved to temperatures that maximized their predation rates, suggesting an indirect positive effect of fish on zooplankton.
Risk assessment model for dispersion of ballast water organisms in shelf seas
Authors: Brickman David
Published: January 2007

The recommendation of mid-ocean exchange of ballast water has resulted in significant release of aquatic invasive species in shelf areas. This paper describes a semiquantitative risk assessment model developed for dispersion of ballast water organisms in shelf seas. The model simulates ballast water exchange as the release of tracer into the surface layer of a circulation model of the Scotian Shelf and Gulf of Maine. Three metrics are proposed to describe the risk of invasion: (i) the time-integrated concentration at a given location (the cumulative exposure index); (ii) the time taken for organisms to reach a given area (the invasion time); and (iii) the onshelf average concentration. A risk equation is derived that computes the relative overall risk of invasion for exchange segments along vessel tracks. Model results confirm the choice of offshelf alternate ballast water exchange zone advised by Department of Fisheries and Oceans, Canada. Low risk segments tend to be adjacent to one another. A four- to eight-fold reduction in invasion risk is possible, although this is likely a lower bound because of the use of monthly mean velocity fields. The model can be run in an operational mode to provide real-time risk assessment for vessel ballast water exchange.
Spatial and environmental correlates of fish community structure in Canadian Shield lakes
Authors: Bertolo Andrea , Magnan Pierre
Published: January 2007

We used data on fish species biomass from 38 lakes of the Canadian Shield (Québec) to determine the contribution of environmental (lake and watershed morphometry) and spatial (e.g., hydrographic connectivity and geographic coordinates) variables on fish community structure. By using a combination of multivariate analyses, we show that nearly half of the variation in the fish community structure is explained by the independent contributions of spatial and environmental factors. Walleye (Sander vitreus) and lake whitefish (Coregonus clupeaformis) were significantly associated with the absence of beaver (Castor canadensis) dams, whereas northern pike (Esox lucius) was positively correlated with beaver dam presence. Altitude and longitude, but not current patterns in lake connectivity, were the main explanatory spatial variables accounting for the observed pattern in fish community structure. Large piscivorous fish were associated with a reduced richness and biomass of small prey, suggesting that predation is a structuring factor in these lakes. By showing that geographic coordinates and altitude are better descriptors of fish community structure than hydrographic connections, our study suggests that past colonization routes are relatively more important than current ones in structuring fish communities at the landscape level. This interpretation is supported by recently published genetic data.
One-dimensional consolidation under general time-dependent loading
Authors: Conte Enrico , Troncone Antonello
Published: January 2007

This paper presents an analytical solution for the analysis of one-dimensional consolidation of saturated soil layers subjected to general time-dependent loading. A simple calculation procedure that makes use of the Fourier series is proposed for practical applications. Both single loads and cyclic loads can be considered by choosing a suitable period for the Fourier series. A number of comparisons with existing theoretical solutions are shown to assess the accuracy of the proposed procedure. Moreover, the experimental results from oedometer tests performed in the present study and from a well-documented case history concerning a large embankment constructed on compressible soils are analysed using this solution to evaluate the coefficient of consolidation of the soil.Key words: one-dimensional consolidation, time-dependent loading, excess pore-water pressure, theoretical solution, Fourier series.
The use of tangent stiffness to characterize the resilient response of unbound crushed aggregates
Authors: Konrad J -M
Published: January 2007

Repeated-load triaxial tests were conducted on crushed granitic base-course material to study the resilient response under different stress paths and compaction states. It has been established that the resilient response of this prestrained unbound granular material is best defined in terms of tangent stiffness (Et) and vertical stress (σv). The data also revealed the existence of a threshold value of tangent stiffness that is essentially dependent on initial confining stress for a given compaction state. When the tangent modulus exceeds this threshold value, a unique relationship between tangent stiffness and vertical stress exists for mobilized shear resistance ratios less than 0.4. This Et–σv relationship is independent of stress path. A simple power law model can be used to predict the resilient response of unbound base-course material and an approximate value of resilient modulus for any desired stress path and initial stress condition. The use of the tangent stiffness – vertical stress model for pavement design appears to be very promising.Key words: granular, material, resilient modulus, triaxial, stress path.
IMMUNITY IN THE NOISY PENNA MODEL
Authors: BIECEK PRZEMYSŁAW , CEBRAT STANISŁAW
Published: January 2007

We have modified the Penna standard sexual model in such a way, that the state of each individual has been determined by the individual fluctuation and the fluctuation of the environment. If the sum of both fluctuations is higher than the assumed limit, the organism dies. Additionally, the individuals can learn the trends of the environment's fluctuations, diminishing their deleterious effects. This mechanism leads to the higher mortality of the youngest individuals and the lowest mortality of individuals just before reaching the minimum reproduction age. These phenomena are observed in any mortality curve describing the age structures of human populations.
HURST EXPONENTS IN FUTURES EXCHANGE MARKETS
Authors: KIM KYUNGSIK , KIM SOO YONG , LEE MINHO , YUM MYUNG-KUL
Published: January 2007

The dynamical behavior of the Korean treasury bond (KTB) futures is investigated using a modified rescaled range (R/S) analysis. Lo's modified R/S analysis as well as classical Hurst's R/S statistics are utilized in order to analyze tick data of KTB futures. The Hurst exponent can be estimated by both classical and modified R/S statistics. The results of this study show that a series of returns has larger long-term correlation as the time lag increases. The Hurst exponent that shows a memory effect for the tick data of KTB futures is larger than 0.5, while the Hurst exponent has a value of nearly 0.5 for the corresponding shuffled data.
RANDOMIZED SZNAJD MODEL
Authors: GWIZDAŁŁA TOMASZ M.
Published: January 2007

This paper presents the results of a modification of well known simple model of social phenomena called Sznajd Model. Although this model has been extensively studied and applied to different topologies I am going to show the influence of slight randomization introduced into the most basic one-dimensional approach. The modification leads to a drastic increase of time needed to reach one of the steady states and to the stabilization of lifetime of governments.
GEOGRAPHICAL EFFECTS ON EPIDEMIC SPREADING IN SCALE-FREE NETWORKS
Authors: XU XIN-JIAN , WANG WEN-XU , ZHOU TAO , CHEN GUANRONG
Published: January 2007

Many real networks are embedded in a metric space: the interactions among individuals depend on their spatial distances and usually take place among their nearest neighbors. In this paper, we introduce a modified susceptible-infected-susceptible (SIS) model to study geographical effects on the spread of diseases by assuming that the probability of a healthy individual infected by an infectious one is inversely proportional to the Euclidean distance between them. It is found that geography plays a more important role than hubs in disease spreading: the more geographically constrained the network is, the more highly the epidemic prevails.
PLURALITY VOTING: THE STATISTICAL LAWS OF DEMOCRACY IN BRAZIL
Authors: ARARIPE LUIS E. , COSTA FILHO RAIMUNDO N. , HERRMANN HANS J. , ANDRADE JOSÉ S.
Published: January 2007

We explore the statistical laws behind the plurality voting system by investigating the election results for the mayor in Brazil in 2004. Our analysis indicate that the vote partition among mayor candidates of the same city tends to be "polarized" between two candidates, a phenomenon that can be closely described by means of a simple fragmentation model. Complex concepts like "government continuity" and "useful vote" can be identified and even statistically quantified through our approach.
THREE GENERATIONS OF SUSY STANDARD MODEL OF NAMBU–GOTO STRING
Authors: DEO B. B.
Published: January 2007

A four-dimensional superstring have been constructed starting from a 26-dimensional bosonic string. Fermions are introduced by noting the Mandelstam's proof of equivalence of two fermions to one boson in 1+1 dimensions. The action of the superstring is invariant under SO (6) ⊗ SO (5) in the worldsheet. It has four bosonic coordinates and 44 Majorana fermions of SO (3, 1). Here the superstring action is shown to be invariant under conformal and superconformal transformations with the usual conformal and superconformal ghosts of the ten-dimensional superstrings. The massless spectrum obtained by quantizing the action, contain vector mesons which are generators of the SO (6) ⊗ SO (5). Using Wilson loops, this product group is proven to descend to Z3 ⊗ SU (3) ⊗ SU (2) ⊗ U (1) without breaking supersymmetry. Thus there are just three generations of quarks and leptons.
MULTIDIFFERENTIAL COMPLEXES AND THEIR APPLICATION TO GAUGE THEORIES
Authors: CONSTANTINESCU RADU , IONESCU CARMEN
Published: January 2007

The construction of a multidifferential complex, i.e. a differential complex with many differential operators, is presented. By a suitable choice of generators, the differentials become anticommuting and can generate a (co)homological resolution. A concrete construction of a n-differential complex is presented and its application to the BRST description of a gauge theory, with a special look at the Yang–Mills model, is considered.
WORLDSHEET COVARIANT PATH INTEGRAL QUANTIZATION OF STRINGS
Authors: VAN TONDER ANDRÉ
Published: January 2007

We discuss a covariant functional integral approach to the quantization of the bosonic string. In contrast to approaches relying on noncovariant operator regularizations, interesting operators here are true tensor objects with classical transformation laws, even on target spaces where the theory has a Weyl anomaly. Since no implicit noncovariant gauge choices are involved in the definition of the operators, the anomaly is clearly separated from the issue of operator renormalization and can be understood in isolation, instead of infecting the latter as in other approaches. Our method is of wider applicability to covariant theories that are not Weyl invariant, but where covariant tensor operators are desired.

After constructing covariantly regularized vertex operators, we define a class of background-independent path integral measures suitable for string quantization. We show how gauge invariance of the path integral implies the usual physical state conditions in a very conceptually clean way. We then discuss the construction of the BRST action from first principles, obtaining some interesting caveats relating to its general covariance. In our approach, the expected BRST related anomalies are encoded somewhat differently from other approaches. We conclude with an unusual but amusing derivation of the value D = 26 of the critical dimension.
BLACK HOLE CROSS-SECTION AT THE LHC
Authors: GINGRICH DOUGLAS M.
Published: January 2007

Black hole production at the Large Hadron Collider (LHC) was first discussed in 1999. Since then, much work has been performed in predicting the black hole cross-section. In light of the start up of the LHC, it is now timely to review the state of these calculations. We review the uncertainties in estimating the black hole cross-section in higher dimensions. One would like to make this estimate as precise as possible since the predicted values, or lower limits, obtain for the fundamental Planck scale and number of extra dimensions from experiments will depend directly on the accuracy of the cross-section. Based on the current knowledge of the cross-section, we give a range of lower limits on the fundamental Planck scale that could be obtained at LHC energies.
SUPERPOSITION MODEL ANALYSIS FOR THE ZERO-FIELD SPLITTING OFMn2+IN SOME CRYSTALS
Authors: JAIN VIMAL KUMAR
Published: January 2007

The Newman superposition model has been applied to second-order zero-field splitting parameter [Formula: see text] taken from the literature for Mn2+in Hg(ClO4)2· 6 H2O , M ″ SiF6·6 H2O (M ″= Fe, Co, Zn ) and M ″ NbOF5·6 H2O (M ″= Co, Zn ). In the calculations, the local lattice relaxation has been taken into account. It is shown that nearly the same value of intrinsic parameter b2=-0.057(8) cm-1is obtained.
A NONLINEAR-OSCILLATOR MODEL FOR STRONG INTERACTION IN MOLECULAR SOLIDS
Authors: GRADO-CAFFARO M. A. , GRADO-CAFFARO M.
Published: January 2007

A theoretical model based upon a one-dimensional anharmonic oscillator is proposed in order to describe strong interactions in molecular solids. Vibrational energy levels are studied in terms of the associated vibrational quantum number; in particular, classical limit is discussed. Kinetic energy corresponding to a typical collision process is calculated. In addition, Morse-type potential interaction is found to be an approximation to our model.
A NOTE ON SPIN-GAUGE EFFECT OF THE BOSE–EINSTEIN CONDENSATES IN ATOMIC GASES
Authors: WANG JUN-PING
Published: January 2007

The Bose–Einstein condensates of the alkali atomic gases trapped in magnetic traps are spinor fields with local "spin-gauge" symmetry.5 Here we show that there is fundamental difference in the manifestation of spin-gauge effects between two low-field-seeking states: |F=2,mF=2〉 and |1,-1〉.
AN ANALYTICAL INVERSION OF THE 180° EXPONENTIAL RADON TRANSFORM WITH A NUMERICALLY GENERATED KERNEL
Authors: HUANG QIU , ZENG GENGSHENG L. , GULLBERG GRANT T.
Published: January 2007

This work presents an inversion algorithm for the exponential Radon transform (ERT) over 180° range of view angles. The algorithm can be applied to two-dimensional parallel beam geometry in single photon emission computed tomography. First the differentiation of the ERT over π is backprojected. A convolutional relation between this backprojected differentiation and the original image is then established. In order to invert the convolution relation, the least-squares method is utilized to obtain a numerically generated filtering kernel, which readily restores the original image. The advantages of the proposed algorithm are, first, it only requires half the view angles of the conventional inversion algorithm, second, it deals with truncation in ERT data in certain situations, and third, the numerically generated filtering kernel can be pre-calculated and stored for later applications. The algorithm is an analytical approach except for the pre-calculated inverse kernel.
Subspace clustering for high dimensional data
Authors: Parsons Lance , Haque Ehtesham , Liu Huan
Published: January 2007

Subspace clustering is an extension of traditional clustering that seeks to find clusters in different subspaces within a dataset. Often in high dimensional data, many dimensions are irrelevant and can mask existing clusters in noisy data. Feature selection removes irrelevant and redundant dimensions by analyzing the entire dataset. Subspace clustering algorithms localize the search for relevant dimensions allowing them to find clusters that exist in multiple, possibly overlapping subspaces. There are two major branches of subspace clustering based on their search strategy. Top-down algorithms find an initial clustering in the full set of dimensions and evaluate the subspaces of each cluster, iteratively improving the results. Bottom-up approaches find dense regions in low dimensional spaces and combine them to form clusters. This paper presents a survey of the various subspace clustering algorithms along with a hierarchy organizing the algorithms by their defining characteristics. We then compare the two main approaches to subspace clustering using empirical scalability and accuracy tests and discuss some potential applications where subspace clustering could be particularly useful.
Modelling and performance evaluation of multiprocessor based packet switches
Authors: Melús J. L. , Sanvicente E. , Magriñá J.
Published: January 2007

This paper presents an approximate analytic model for the performance analysis of a class of multiprocessor based packet switches. For these systems, processors and common memory modules are grouped in clusters, each of them composed of several processor-memory pairs that communicate through a multiple bus interconnection network. Intercluster communication is also achieved using one or more busses. The whole network operates in a circuit-switched mode.

After access completion, a processor remains active for an exponentially distributed random time. Access times are also exponential with different means, depending upon the location (local, cluster, external) of the referenced module. The arbitration is done on a priority basis.

The performance is predicted by computing the average number of switched packets per time unit. Other related indexes are also given. Numerical results are obtained rather easily by solving a set of two algebraic equations. Simulation is used to validate the accuracy of the approximations used in the model.
Memory-reference characteristics of multiprocessor applications under MACH
Authors: Agawal A. , Gupta A.
Published: January 2007

Shared-memory multiprocessors have received wide attention in recent times as a means of achieving high-performance cost-effectively. Their viability requires a thorough understanding of the memory access patterns of parallel processing applications and operating systems. This paper reports on the memory reference behavior of several parallel applications running under the MACH operating system on a shared-memory multiprocessor. The data used for this study is derived from multiprocessor address traces obtained from an extended ATUM address tracing scheme implemented on a 4-CPU DEC VAX 8350. The applications include parallel OPS5, logic simulation, and a VSLI wire routing program. Among the important issues addressed in this paper are the amount of sharing in user programs and in the operating system, comparing the characteristics of user and system reference patterns, sharing related to process migration, and the temporal, spatial, and processor locality of shared blocks. We also analyze the impact of shared references on cache coherence in shared-memory multiprocessors.
Optimal allocation of multiple class resources in computer systems
Authors: Tantawi A. N. , Towsley G. , Wolf J.
Published: January 2007

A class-constrained resource allocation problem is considered. In this problem, a set of
M
heterogeneous resources is to be allocated optimally among a set of
L
users belonging to
K
user classes. A set of class allocation constraints, which limit the number of users of a given class that could be allocated to a given resource, is imposed. An algorithm with worst case time complexity

O(M (LM + M
2
+ LK))

is presented along with a proof of its correctness. This problem arises in many areas of resource management in computer systems, such as load balancing in distributed systems, transaction processing in distributed database systems, and session allocation in time-shared computer systems. We illustrate the behavior of this algorithm with an example where file servers are to be allocated to workstations of multiple classes.
Multiprogramming and program behavior
Authors: Graham G. Scott , Denning Peter J.
Published: January 2007

Dynamic multiprogramming memory management strategies are classified and compared using extant test data. Conclusions about program behavior are then drawn.
A general-purpose software measurement tool
Authors: Ferrari Domenico , Liu Mark
Published: January 2007

A software measurement tool designed for the users of PRIME, an interactive system being developed, is presented. The tool, called SMT, allows its user to instrument a program, modify a pre-existing instrumentation and specify how the collected data are to be reduced by typing in a few simple commands. The user can also write his own measurement routines, which specify the actions to be taken at event detection time, and submit them to the SMT; after checking their correctness, the SMT deals with them as with its built-in, standard measurement routines. The design goals of a general-purpose tool like the SMT are discussed, and the prototype version of the tool, which has been implemented, is described from the two distinct viewpoints of a user and of a measurement-tool designer. An example of the application of the prototype to a measurement problem is illustrated, the reasons why not all of the design goals have been achieved in the implementation of the prototype are reviewed, and some of the foreseeable extensions of the SMT are described.
Measurements of the virtual memory demands of Algol-60 programs (Extended Abstract)
Authors: Batson A. P. , Brundage R. E.
Published: January 2007

Programming languages such as Algol-60 use block structure to express the way in which the name space of the current environment, in the contour model (1) sense of that word, changes during program execution. This dynamically-varying name space corresponds to the virtual memory required by the process during its execution on a computer system. The research to be presented is an empirical study of the nature of the memory demands made by a collection of Algol-60 programs during execution. The essential characteristics of any such resource requiest are the amount of memory requested, and the holding time for which the resource is retained and these distributions will be presented for several components of the virtual memory required by the Algol programs.
Computing failure
Authors: Glass Robert L.
Published: January 2007

Computing people can learn from failure as well as success. Most professional papers deal only with the latter ... yet it is well known that some of our most lasting learning experiences are based on failure. This paper is a lighthearted, anecdotal discussion of a computing failure, with an underlying message that sharing the sometimes embarrassing truths about What Goes Wrong In Our Field is at least as illuminating as more serious discussions about Things That Look Promising.

There are some necessary defense mechanisms to be dealt with in discussing failure. People who have failed in general do not want the world to know about it. Perhaps even more so, companies which have failed also do not want the world to know about it. As a result, the content of this paper is fictionalized to some extent. That is, company names and people names are creations of the author, and there are corresponding distortions in some story details. However, the computing meat of the paper, the basis for the failure learning experience, is untouched.
The establishment and use of measures to evaluate the quality of software designs
Authors: Yin B. H. , Winchester J. W.
Published: January 2007

It has been recognized that success in producing designs that realize reliable software, even using Structured Design, is intimately dependent on the experience level of the designer. The gap in this methodology is the absence of easily applied quantitative measures of quality that ease the dependence of reliable systems on the rare availability of expert designers.

Several metrics have been devised which, when applied to design structure charts, can pinpoint sections of a design that may cause problems during coding, debugging, integration, and modification. These metrics can help provide an independent, unbiased evaluation of design quality. These metrics have been validated against program error data of two recently completed software projects at Hughes. The results indicate that the metrics can provide a predictive measure of program errors experienced during program development.

Guidelines for interpreting the design metric values are summarized and a brief description of an interactive structure chart graphics system to simplify metric value calculation is presented.
Software acceptance testing that goes beyond the book
Authors: Martin K. A.
Published: January 2007

The design of software acceptance tests is as important to meeting contract goals as is the design of algorithms. This statement is particularly significant on fixed price contracts with tight schedules. An extreme instance of the demand placed on acceptance testing can be found in software projects wherein the only rigorous testing that required the Computer Program Configuration Item (CPCI) to exercise its repertoire of load and store instructions was the Formal Qualification Test (FQT). This paper is about such a project, the lessons learned from it, and provides an effective test approach for fixed price contracts.

A word or two about the project is appropriate to establish the context that underscores the impact of the above assertion. Initially 30K (core words), 16-bit program instructions were to be developed within one year using a Varian 73 computer with 32K words of memory for a Command and Control application under a fixed price contract. A set of a priori conditions existed that tended to convey the impression that the inherent risks of this endeavor were reasonable. They were the “facts” that:

Of the 30K (core words) to be written, 30% of this code already existed and would be used.

Contractor standards would be allowed for documentation with limited use of Military Specifications

No formal Design Reviews or audits would accompany the deliverable CPCI.

Existent executive software would suffice.

A competent and enthusiastic team was committed to the effort.
A framework for the measurement of software quality
Authors: Cavano Joseph P. , McCall James A.
Published: January 2007

Research in software metrics incorporated in a framework established for software quality measurement can potentially provide significant benefits to software quality assurance programs. The research described has been conducted by General Electric Company for the Air Force Systems Command Rome Air Development Center. The problems encountered defining software quality and the approach taken to establish a framework for the measurement of software quality are described in this paper.
A measurement of structure for unstructured programming languages
Authors: Cobb Gary W.
Published: January 2007

Software Science is a field of Natural Science which deals with the development of measurements which reveal properties of software programs. These measurements are qualified as to their degree of correlation to human beings being able to construct or understand a subject program. Maurice Halstead has pioneered much of the theories in this field ((5) through (10)), which applies statistical and psychological testing techniques to the evaluation of the measurements. The basic inputs to the Halstead predictors are easily measured: the number of distinct operators and operands, and the number of occurrences of the operators and operands. Due to the statistical nature of the measurements, there can be erroneous results when applying them to small sample spaces. However, the predictors are very adequate when applied to large samples, that is, large software systems. In an excellent review article by Fitzsimmons and Love (4), it is pointed out that several of the estimators defined by Halstead assumed that the subject programs were well-structured, and inaccurancy in the predictors can result if they are applied to "unpolished" programs. In fact, Halstead qualified six classes of impurities in code which can cause the length predictor to be inaccurate.

The definition of volume for software, another predictor introduced in Halstead's book, is related to the level of the specification of the program. An algorithm which is written in assembly language will have a greater volume than the same algorithm written in Pascal, due to the richness of the semantic constructs that are available in the higher-level languages. Hence, this predictor is language dependent.
Using performance metrics in system design
Authors: Lockett Joann
Published: January 2007

Complexities of system design are great and often lead designers to be inward looking in their analyses. Knowledge from various fields can be of benefit in designing systems [1]. Management accountants can describe economic effects of delays in closing schedules, psychologist can provide significant insights into the behavioral characteristics of users to complex command syntax, computer performance analysts can provide alternatives to describe and to measure responsiveness of systems. Even in the case of an innovative system design, the designer can employ such approaches to identify incipient problems and create alternatives with increased cost effectiveness. This paper describes how
performance metrics
can be used effectively to support system design.
The value of a proper software quality assurance methodology
Authors: Tighe Michael F.
Published: January 2007

This paper describes the experiences of a project development team during an attempt to ensure the quality of a new software product. This product was created by a team of software engineers at Digital Equipment Corporation, a mainframe manufacturer. As a result, the definition of “to ensure the quality of a software product” meant minimizing the maintenance costs of the new product. Ease of maintenance and a low bug rate after release to the customer were very important goals from the beginning of the project.

This paper compares the degree of application and resultant effects of several software quality assurance methodologies upon different parts of the final product. Many of the product's subsystems were created using all of the discussed methodologies rigorously. Some subsystems were created with little or no use of the methodologies. Other subsystems used a mixture. The observed quality of the various subsystems when related to the methodology used to create them provides insights into the interactions between the methodologies. These observations also supply additional experience to reinforce established beliefs concerning the value of quality assurance methodologies.
Effects of buffered memory requests in multiprocessor systems
Authors: Briggs Fayé A.
Published: January 2007

A simulation model is developed and used to study the effect of buffering of memory requests on the performance of multiprocessor systems.

A multiprocessor system is generalized as a parallel-pipelined processor of order (s,p), which consists of p parallel processors each of which is a pipelined processor with s degrees of multiprogramming, there can be up to s*p memory requests in each instruction cycle. The memory, which consists of N(=2
n
) identical memory modules, is organized such that there are l(=2
i
) lines and m(=2
n-i
) identical memory modules, where each module is characterized by the address cycle (address hold time) and memory cycle of a and c time units respectively.

Too large an l is undesirable in a multiprocessor system because of the cost of the processor-memory interconnection network. Hence, we will show how effective buffering can be used to reduce the system cost while effectively maintaining a high level of performance.
An exact solution method for the general class of closed separable queueing networks
Authors: Zahorjan John
Published: January 2007

In this paper we present a convolution algorithm for the full class of closed, separable queueing networks. In particular, the algorithm represents an alternative method to those already known for the solution of networks with class changes, and is the first efficient algorithm to deal with Lam-type networks [11].

As an application of the algorithm, we study a simple queueing network with disk I/O devices connected to a single CPU through a single channel. The algorithm is then used to develop a simple, accurate approximation for the blocking of disk devices that takes place when a customer using a disk is waiting for or in service at the channel.
Computational algorithms for product form queueing networks
Authors: Chandy K. Mani , Sauer Charles H.
Published: January 2007

In the last two decades there has been special interest in queueing
networks
with a
product form
solution. These have been widely used as models of computer systems and communication networks. Two new computational algorithms for product form networks are presented. A comprehensive treatment of these algorithms and the two important existing algorithms, convolution and mean value analysis, is given.
Program restructuring for block structured languages
Authors: Kumar Gopa , Nute C. Thomas
Published: January 2007

Prior studies of program restructuring to increase the degree of locality of a program in a paged virtual memory system were restricted to statically allocated codes only. This work develops a restructuring methodology for block structured languages like Algol, with dynamic memory allocation. We subsequently restructure and analyze different classes of programs using this methodology and study the performance gains realized with different restructuring heuristics.
Calculating equilibrium probabilities for λ(n)/C
k
/1/N queues
Authors: Marie Raymond
Published: January 2007

Equilibrium state distributions are determined for queues with load-dependent Poisson arrivals and service time distributions representable by Cox's generalized method of stages. The solution is obtained by identifying a birth-death process that has the same equilibrium state distribution as the original queue. Special cases of two-stage (C
2
) and Erlang-k (E
k
) service processes permit particularly efficient algorithms for calculating the load - dependent service rates of the birth-death process corresponding to the original queue. Knowing the parameters of the birth-death process, the equilibrium state probabilities can be calculated straight-forwardly. This technique is particularly useful when subsystems are reduced to flow-equivalent servers representing the complementary network.
Hardware configuration selection through discretizing a continuous variable solution
Authors: Wagner Robert A. , Trivedi Kishor S.
Published: January 2007

This paper extends a previous model for computer system configuration planning developed by the authors. The problem is to optimally select the CPU speed, the device capacities, and file assignments so as to maximize throughput subject to a fixed cost constraint. We advocate solving this essentially discrete problem in continuous variables followed by an appropriate discretization. The discretization error thus committed is analyzed in detail.
A model of shared dasd and multipathing
Authors: Bard Yonathan
Published: January 2007

This paper presents a model of an I/O subsystem in which devices can be accessed from multiple CPUs and/or via alternative channel and control unit paths. The model estimates access response times, given access rates for all CPU-device combinations. The systems treated are those having the IBM System/370 architecture, with each path consisting of a CPU, channel, control unit, head of string, and device with rotational position sensing. The path selected for an access at seek initiation time remains in effect for the entire channel program.

The computation proceeds in three stages: First, the feasibility of the prescribed access rates is determined by solving a linear programming problem. Second, the splitting of access rates among the available paths is determined so as to satisfy the following principle:

The probability of selecting a given path is proportional to the probability that the path is free.

This condition leads to a set of nonlinear equations, which can be solved by means of the Newton-Raphson method.

Third, the RPS hit probability, i.e. the probability that the path is free when the device is ready to transmit, is computed in the following manner: From the point of view of the selected path, the system may be viewed as being in one of 25 possible states. There are twelve different subsets of states whose aggregate probabilities can be computed from the (by now) known flow rates over the various paths. The maximum entropy principle is used to calculate the unknown state probabilities, with the known aggregate probabilities acting as constraints. The required RPS hit probability can be computed easily once the state probabilities have been determined. Explicit formulas are given for all these quantities. Empirically derived formulas are used to compute the RPS miss probability on subsequent revolutions, given the probability on the first revolution.

The model is validated against a simulator, showing excellent agreement for systems with path utilizations up to 50 percent. The model is also validated against measurements from a real three-CPU system with 31 shared devices. In this validation, the I/O subsystem model acts as a common submodel to three copies of a system model, one for each CPU. Estimated end-user transaction response times show excellent agreement with the live measurements.
Computer capacity planning using queueing network models
Authors: Lo T. L.
Published: January 2007

This paper presents several computer capacity planning case studies using a modeling tool, BEST/1, derived from the theory of queueing networks. All performance predictions were evaluated based on the selected service levels such as response times and throughputs. Advantages and disadvantages of using the modeling approach are also briefly discussed.
Analysis of design alternatives for a packet switched I/O system
Authors: Upton Richard A. , Tripathi Satish K.
Published: January 2007

This paper describes an application of analytical modeling to the design and evaluation of a general purpose, packet-switched image processing system that will soon enter an implementation phase. A bottom-up modeling approach is used to evaluate such design issues as optimal packet size, optimal channel access method(s), and required number of processors and disks. Based on the characteristics of various hardware components and the predicted workload, specific design recommendations are made.
Optimal replication of parallel-read, sequential-write systems
Authors: Coffman E. G. , Gelenbe Erol , Wood Roger C.
Published: January 2007

Frequently used computer elements that can be written by at most one process at a time constitute important bottlenecks in multiprocessor system operation, particularly when such elements are accessible only serially. Hardware devices, data files, system tables and critical sections in general may be examples of such elements. One common way to relieve this congestion is to provide several copies of the element, which can then be read (used) in parallel. However, the requirement that writing (changing) remain sequential means that writing times increase with the number of copies provided. The optimization question in this trade-off is the main concern of this paper.

A probability model of such a system is formulated with the objective of obtaining read-rate capacities as a function of read/write loads and the number of copies provided. The above optimization problem is expressed in terms of these results and then solved. In particular, it is shown how to select the number of copies that maximizes the read-rate capacity for given system parameters. Two distinct operating regimes, based on how interrupted read operations are restarted, are analyzed.
The solution of certain two-dimensional markov models
Authors: Fayolle G. , King P. J.B. , Mitrani I.
Published: January 2007

A class of two-dimensional Birth-and-Death processes, with applications in many modelling problems, is defined and analysed in the steady-state. These are processes whose instantaneous transition rates are state-dependent in a restricted way. Generating functions for the steady-state distribution are obtained by solving a functional equation in two variables. That solution method lends itself readily to numerical implementation. Some aspects of the numerical solution are discussed, using a particular model as an example.
Structured life-cycle assumptions
Authors: Bell Thomas E.
Published: January 2007

New programmers, some managers, and lots of users don't understand the advantages of a structured software life-cycle. However, only a single experience with coding while designing will convince any incipient software engineer that a controlled process is needed from the time of system concept though the last maintenance phase. Software Configuration Management has become almost a religion, and EDP auditors have even encountered a few systems that appear to have been specified, then designed, then implemented, then tested, and finally installed—all before maintenance and redefinition occurred. Perhaps the millennium has finally arrived, and software people will soon live in a controlled world with rational practices.

If you are tempted to believe the foregoing prediction, read the latest issue of FORTUNE, the WALL STREET JOURNAL, or COMMERCE BUSINESS DAILY and note a few problems that may divert us from the path to Nirvana. Data Processing supports commercial, educational, industrial, and governmental activities that are frequently (and repeatedly) redirected. Under circumstances of a largely random environment with thorough business planning a rarity, a critical support activity can expect to be redirected frequently. New ideas will be sliced into partly-completely DP projects, and users “analytical analyses” will become DP systems as if by magic.