Mutual Consistency Research Articles

Combined Model for Signal Control and Route Choice in Urban Traffic Networks

Traffic signals have a significant effect on the choice of routes by motorists in urban areas. They are of primary importance in the development of advanced traffic management strategies that involve dynamic rerouting of traffic flows through signal-controlled street networks. A combined network model that simultaneously accounts for both the route choices made by motorists and the desired signal controls to match these choices is presented. Given origin-destination travel demand information, the model generates signal controls to optimize network performance and calculates the resulting traffic volumes in the network. This optimization model inherently reflects the mutual consistency between traffic flows and signal controls. The model is applicable to both fixed-time and demand-responsive signals. Computational procedures and sample network solutions are presented.

Crustal deformations in the mediterranean area computed from SLR and GPS observations

Space geodesy provides an efficient technique to determine contemporary crustal deformations. This paper discusses the computation of tectonic motions in the Mediterranean area from observations acquired by Satellite Laser Ranging (SLR) and Global Positioning System (GPS) instruments. The SLR contribution is based on measurements on LAGEOS-1, taken in the period September 1983 to December 1992. For this analysis, the period was divided into 38 consecutive intervals. An independent station coordinates solution was computed for each subinterval. During this 9.3 year interval, the WEGENER project organized four mobile SLR observation campaigns in the Mediterranean region, resulting in three or four independent position solutions for the majority of the sites in this area. The GPS contribution is based on observations taken during the Euref 89 campaign, which took place from May 16 to 28, 1989, and during the WEGENER/GPS-92 campaign, which took place from July 29 to August 3, 1992, as a sub-campaign for the IGS Epoch'92 campaign. Most of the space-geodetic reference points in the Mediterranean area were occupied with GPS receivers during both campaigns, providing two valuable additional position solutions. The time-series of position solutions for each station are converted into individual station motion vectors. The horizontal components of the latter reveal a clear and consistent picture of the deformations taking place in the area: the northward motion of Arabia, the lateral escape to the west of Anatolia, the NE-SW expansion in the Aegean Basin and the northward motion of Africa being transduced into the central part of the Mediterranean. The results are in agreement with the qualitative kinematical models for this region, derived from geophysical evidence. The vertical station motion solutions are generally very small and insignificant from a statistical point of view. The internal and mutual consistency of the independent SLR and GPS network solutions is also investigated. The agreement is shown to be at the level of 5–20 mm.

A heuristic optimization model of coordination strategies for CIM databases

Coordination among computer integrated manufacturing databases has become one of the key difficulties in the implementation of an integrated system. The issue of how to implement interdependency among CIM databases has some alternative technological solutions, trading off various levels of mutual consistency against various levels of the system throughput. Although these alternatives and their formalization are important issues in the database theory perspective, this research deals with an engineering issue of devising a methodology to select among these alternatives in any given case. A heuristic optimization model, with worst time complexity of O(N 2) is presented. Its effectiveness is analyzed with a case study and a series of sensitivity analysis activations. This is a first attempt to solve this problem. Our empirical results show that the overall system performance, as reflected by a system's goal-function, is substantially improved by the use of our model, relative to intuitive or trivial solutions.

Comments on the Mori Formula for Transport Coefficients

Three decades ago, the quantum Langevin equation (Mori formula) was used to reformulate the linear response theory (Kubo formula). Since then, the Mori formula has often been used to evaluate transport coefficients, but only within the Born approximation. In the present study, we obtain a rigorous expression for the transport coefficients as a series expansion in terms of the projection operator. We then evaluate the optical conductivity for a free electron system with impurity scattering in order to discuss the mutual consistency between the Mori formula and the Kubo formula.

DGDBM

This paper describes a set of facilities for programming distributed transactions over replicated files which are accessed by primary key. The files are located on several computers communicated by a network. Each site has the set of GNU dbm (Gdbm) routines for local file management [15]. Above this platform we have built an interface and a set of services for distributed transaction programming. The resulting programming environment,"DGDBM", offers transparency in relation to data distribution and data replication, giving a centralized vision to the programmer. It assures the functions of management of distributed transactions like as failure recovery, mutual consistency between copies and concurrence control. DGDBM is an useful support for distributed application programming over replicated files in UNIX networks and it is available as an API (application programming interface) for the C programmer. This paper describes the services offered by DGDBM to the programmer, the architecture of the system, the adopted solutions for distributed transaction management, the general aspects of design and implementation and the perspectives and planned extensions for this project.

Analysis of the FK5 System in the Equatorial Zone

15 catalogues produced in the eighties and 12 catalogues of the sixties-seventies have been used to assess the consistency of the FK5 system with observations in the declination zone from −30° to 30°. Positions of the FK4-based catalogues have been transformed at the equinox and equator J2000.0. Classical δ-dependent and α-dependent systematic differences (Cat-FK5) have been formed for individual instrumental systems of the catalogues by a method close to the classical Numerical Method. The weighted mean instrumental systems for the two subsets of catalogues centered at the epochs 1970 (MIS 60–70) and 1987 (MIS 80) and for all types of systematic differences have been constructed. The mean errors of the total systematic differences in α and δ have been estimated as 14 mas and 21 mas, respectively, for the catalogues of the 60-70ies, and 10 mas in both α and δ for the catalogues of the 80ies.It has been found that the mutual consistency of individual instrumental systems of catalogues of the 80ies with respect to δ-dependent systematic differences is superior by the factor 1.5 comparing with the catalogues of 60-70ies, while the consistency of both catalogue selections with respect to α-dependent systematic differences is comparable. Random accuracy of the FK5 positions and proper motions at the epochs under analysis has been assessed as close to expected from the formal considerations. Actual systematic discrepancies of the FK5 with observations at the respective epochs have been detected. For systematic differences δαδ cosδ and δδδ, the absolute deviations of the MIS 80 are, in general, within 40 mas, those of the MIS 60-70 are within 30 mas. For systematic differences δαα cosδ and δδα, the absolute deviations reach 30-40 mas for both MIS. For total systematic differences, local deformations of the FK5 system in the equatorial zone in both right ascension and declination has been found exceeding expected ones from the formal errors of the FK5 system by a factor about 1.5 for the MIS 60-70, and by a factor about 2 for the MIS 80. Consistency in area distribution between both MIS for the total systematic differences δαcosδ has been detected. Quick degradation of the FK5 system with time due to optimistic estimation of the errors of its proper motion system is supposed to be one of the main causes of its discrepancies with observations. The results in declination are recognized to be less reliable due to larger inconsistency of the individual instrumental systems.Before the next space astrometric mission will be realized, ground-based observations will continue to be the only available check of an external systematic accuracy of the HIPPARCOS catalogue. Evidently, random and, possibly, systematic accuracy of each individual catalogue observed from the Earth surface would be inferior to that of the HIPPARCOS catalogue. Taken as an ensemble, however, a certain selection of catalogues might give a rather definite idea about the actual distortions of the HIPPARCOS system. This study shows to which level of accuracy such ensembles of different selections of catalogues might check the HIPPARCOS system in the equatorial zone. The analysis of the FK5 gives also an idea about levels of random and systematic discrepancies which may be expected in the equatorial zone when the HIPPARCOS catalogue will be compared with the FK5 at different epochs.

A mass spectrometric study of the dissociation of the gaseous diatomic tellurium molecule

The dissociation equilibrium, Te 2(g) = 2Te(g), was evaluated from the partial pressures of Te(g) and Te 2(g) over different metal-tellurides (where the metal = Fe, Cr, Ni or Mo). The equilibrium constants, deduced as a function of temperature (820–1285 K), correspond to a range of monomer-to-dimer ratios, i.e. p(Te)/ p(Te 2) varying from ~ 0.02 to 1. They are consistent with the available results corresponding to higher temperatures (1195–1467 K), and therefore, the two sets of data were combined into the following dissociation constant-temperature relation (820–1467 K): ▪ The resulting third-law dissociation enthalpy of Te 2(g), 257.6 ± 4.1 kJ mol −1, which we recommend, is in excellent agreement with photoionization or spectroscopie results. The pressure-independent reaction, Te(g) + Te (in condensed phase) = Te 2(g) was also evaluated and the following relation was obtained: ▪ This evaluation confirmed the mutual consistency of the p(Te) and p(Te 2) values employed to deduce the dissociation constant-temperature relation as well as the dissociation energy reported here. Furthermore, a correlation between the monomer-to-dimer ratio in the vapour phase to the activity of tellurium in the condensed phase is brought out.

Consistency Check for Trends in Surface Temperature and Upper-Level Circulation: 1950–1992

A time series of 43 years of observed monthly mean air temperature at 109 sites in the 48 contiguous United States is compared to monthly mean air temperature specified from hemispheric gridded 700-mb heights. Because both upper-air and surface data have problems that may limit their use in climate change studies, this comparison could be considered a mutual consistency check. Cooling (by about 0.5°C) from 1951 to about 1970 and subsequent warming (also by 0.5°C) that continues through the present are found in both datasets, indicating that these interdecadal changes are probably real. In the List several years the specified temperatures were often colder than those observed. This prompted an investigation of whether the “residual” (specified minus observed) has recently been large (and negative) compared to the earlier part of the record. It was found that for the same 700-mb height field, surface temperatures were almost a degree Celsius warmer in the last few years than they were in the early 1950s, but considering the variability of the residuals over the 1950–92 period, the recent cold residuals may not yet be strikingly unusual. By comparing the full set of 109 stations to a “clean” subset of 24, the impact of common problems in surface data (station relocation, urbanization, etc.) was found to be quite small. The rather favorable comparison of observed surface temperatures and specified surface temperatures (which suffer from upper-air analysis / observation changes over the years) indicates that their respective data problems do not appear to invalidate their use in studies of interdecadal temperature change.

Riometer observations at Sanae (L = 4.0) related to solar proton events

Atmospheric ionization by protons of integral intensity above a cutoff of 0.86 GV at Sanae is too small to record a riometer absorption above noise even during the large ground‐level enhancements (GLEs) of September 29 and October 19 and 24, 1989. However, linear increases may be depicted in the absorptions of 20‐, 30‐, and 51.4‐MHz cosmic radio noise that ranged from 0.25 dB per hour at 30 MHz for a GLE with a rising phase of 26% per hour to 0.81 dB per hour for a GLE of 360% per hour. Lowering of cutoff rigidity by magnetospheric ring currents to give direct access to solar flare protons of rigidity below 0.86 GV or precipitation of energetic magnetospheric electrons due to magnetic activity may be ruled out. Mutual consistency appears between the rates in ground‐level solar proton enhancements and the rates of increases in absorptions at all three of the frequencies for all three events. This suggests that nonrelativistic solar protons should have traversed the geomagnetic field lines to be precipitated at Sanae. This traversal may be due to equatorward gradient and curvature drifts from the polar cap region, a westward longitudinal drift along L = 4.0, and subsequent precipitation into the atmosphere at Sanae due to the South Atlantic Magnetic Anomaly. Preceding these linear increases, solar flare effects with absorption maxima coincident with the maxima of solar flare X rays and the 2.2‐MeV gamma ray line have been observed. The rates of recovery in absorption that are faster than that of the 0.5‐ to 4‐Å X rays suggest that these absorptions are due to ionization caused by still shorter wavelength electromagnetic radiation.

A token-based synchronization scheme for distributed real-time databases

Schedulers for real-time replicated database systems must satisfy two major requirements: transactions should meet their timing constraints, and mutual consistency of replicated data should be preserved. In this paper, we present a synchronization scheme, prove its correctness, and evaluate its performance in a distributed real-time database system. The algorithm adopts a token-based scheme for replication control and attempts to balance the urgency of real-time transactions with the conflict resolution policies. In addition, the algorithm employs epsilon-serializability (ESR), a new correctness criterion which is less stringent than conventional one-copy-serializability. The algorithm is flexible and very practical, since no prior knowledge of the data requirements or the execution time of each transaction is required.

New techniques of applying multi-wavelength anomalous scattering data

Several different methods of using multi-wavelength anomalous scattering data are described and illustrated by application to the solution of the known protein structure, core streptavidin, for which data at three wavelengths were available. Three of the methods depend on the calculation of Patterson-like functions for which the Fourier coefficients involve combinations of the anomalous structure amplitudes from either two or three wavelengths. Each of these maps should show either vectors between anomalous scatterers or between anomalous scatterers and non-anomalous scatterers. While they do so when ideal data are used, with real data they give little information; it is concluded that these methods are far too sensitive to errors in the data and to the scaling of the data-sets to each other. Another Patterson-type function, the P s function, which uses only single-wavelength data can be made more effective by combining the information from several wavelengths. Two analytical methods are described, called AGREE and ROTATE, both of which were very successfully applied to the core streptavidin data. They are both made more effective by preprocessing the data with a procedure called REVISE which brings a measure of mutual consistency to the data from different wavelengths. The best phases obtained from AGREE lead to a map with a conventional correlation coefficient of 0.549 and this should readily be interpreted in terms of a structural model.

Regeneration with virtual copies for distributed computing systems

The authors consider the consistency control problem for replicated data in a distributed computing system (DCS) and propose a new algorithm to dynamically regenerate copies of data objects in response to node failures and network partitioning in the system. The DCS is assumed to have strict consistency constraints for data object copies. The algorithm combines the advantages of voting-based algorithms and regeneration mechanisms to maintain mutual consistency of replicated data objects in the case of node failures and network partitioning. The algorithm extends the feasibility of regeneration to DCS on wide area networks and is able to satisfy user queries as long as there is one current partition in the system. A stochastic availability analysis of the algorithm shows that it provides improved availability as compared to previously proposed dynamic voting algorithms. >

Remote sensing of auroral E region plasma structures by radio, radar, and UV techniques at solar minimum

The unique capability of the Polar BEAR satellite to simultaneously image auroral luminosities at multiple ultraviolet (UV) wavelengths and to remote sense large‐scale (hundreds to tens of kilometers) and small‐scale (kilometers to hundreds of meters) plasma density structures with its multifrequency beacon package is utilized to probe the auroral E region in the vicinity of the incoherent scatter radar (ISR) facility near Sondrestrom. In particular, we present coordinated observations on two nights obtained during the sunspot minimum (sunspot number <10) January–February 1987 period when good spatial and temporal conjunction was obtained between Polar BEAR overflights and Sondrestrom ISR measurements. With careful coordinated observations we were able to confirm that the energetic particle precipitation responsible for the UV emissions causes the electron density increases in the E region. These E region electron density enhancements were measured by the ISR at Sondrestrom. The integrations up to the topside of these ISR electron density profiles were consistent with the total electron content (TEC) measured by the Polar BEAR satellite. An electron transport model was utilized to determine quantitatively the electron density profiles which could be produced by the particle precipitation, which also produced multiple UV emissions measured by the imager; these profiles were found to be in good agreement with the observed ISR profiles in the E region. Surprisingly large magnitudes of phase and amplitude scintillations were measured at 137 and 413 MHz in the regions of TEC enhancements associated with the particle precipitation. Steep phase spectral slopes with spectral index of 4 were found in these regions. Strength‐of‐turbulence computations utilizing the ISR electron density profiles and observed characteristics of phase and amplitude scintillations are interpreted in terms of an irregularity amplitude varying between 10 and 20% at a several‐kilometer outer scale size in the E region extending approximately 50 km in altitude. This outer scale size is also consistent with the measured phase to amplitude scintillation ratio. An estimate of the linear growth rate of the gradient‐drift instability in the E region shows that these plasma density irregularities could have been generated by this process. The mutual consistency of these different sets of measurements provides confidence in the ability of the different techniques to remote sense large‐ and small‐scale plasma density structures in the E region at least during sunspot minimum when the convection‐dominated high‐latitude F region is fairly weak.

Roles of Resource and Data Contention on the Performance of Replicated Distributed Database Systems

The consistency problem in replicated distributed database systems is complicated by the requirement to ensure mutual consistency across the nodes. Traditionally, it is solved by the semi-distributed approach in which all computations of a transaction are carried out at the site of its origination. In this paper, the impact of resource and data contention on the performance of Semi-distributed Algorithm (SDA) has been studied and is compared with Fully-distributed Algorithm (FDA) under different degree of communication overheads with the objective of obtaining some practical guidelines for the design of such systems. Centralized Static Two Phase Locking (CS2PL) is the concurrency control protocol adopted in both models to ensure the serializability of transactions. Results indicate that for both algorithms, data contention rather than resource contention is the dominant factor in affecting the system performance especially when granularity of database is fine. The study also suggests that SDA is more suitable for systems with low communication overheads whereas FDA performs better for systems with high resource contention in communication links and small transaction sizes. FDA has the additional advantage of greater tolerance towards unreliable networks.

Stark Broadening Parameters of C IV Lines for Stellar Plasma Research

In order to complete available C IV broadening data needed for stellar plasma research, we have calculated Stark broadening parameters for 69 C IV multiplets of large principal quantum number. The results along with a discussion of the Stark broadening parameter regularities within spectral series will be published elsewhere (Dimitrijevic and Sahal–Brechot, 1992). As an example in Figs 1 and 2 the case of C IV np2P0 − 9s2S transitions, is presented. We can see that particularly for shifts the changes of Stark broadening parameters are relatively small, permitting the interpolation of new data or critical evaluation of mutual consistency of existing data.

Implementing atomicity in two systems: techniques, tradeoffs, and experience

This paper presents our experience with implementing atomicity in two systems: the QuickSilver distributed file system and the Starburst relational database manager. Each of these systems guarantees that certain collections of operations done on behalf of their clients execute atomically, despite process, machine, or network failures. In this paper we describe the atomic properties implemented by each system, present the algorithms and mechanisms used, examine the similarities and differences between the two systems, and give the rationale for different design decisions. We demonstrate that the support of atomicity with high performance requires a variety of techniques carefully chosen to balance the amount of data logged, the level of concurrency allowed, and the mutual consistency requirements of sets of objects, The main goal is to help others implement efficient systems that support atomicity. >

Using semantic knowledge of transactions to improve recovery and availability of replicated data

Replication in distributed computing systems provides improved availability and reliability in the event of site failure and network partitioning. However, if strict mutual consistency is required, transactions can be processed in at most one partition, thereby reducing availability. We present a consistency control algorithm that relaxes strict mutual consistency criteria, and allows concurrent processing in all partitions. Inconsistency of data objects in different partitions is resolved at the time of merging the partitions when recovery occurs. The basis of our algorithm is a new merge mechanism that utilizes available semantic information about the data objects and transaction types. We present a formal proof of correctness of the algorithm. Results from a simulation model show that our algorithm performs better than a previously proposed approach that uses compensating transactions to sacrifice serializability of replicated data.

Credible assignments in coordination games

This paper uses the experimental method to examine an arbiter's ability to determine the outcome of two-person coordination games. All of the arbiter's assignments in the experiments were strict equilibrium points, but some assignments violated payoff-dominance or symmetry. An assignment that corresponds to the game's outcome is a credible assignment. The experiments test the hypothesis that an assignment to a strict equilibrium is a credible assignment. Our subjects did not find the individual rationality and mutual consistency of an equilibrium assignment to be sufficient reason for implementing the assignment when doing so conflicts with payoff-dominance or symmetry.

Validation and assimilation of Seasat altimeter wave heights using the WAM wave model

The mutual consistency of the Seasat global data sets of scatterometer winds and altimeter wave heights is investigated for the complete Seasat period using the third‐generation wave model WAM. The wave model was driven by surface (1000 hPa) wind and surface stress fields constructed by the Goddard Laboratory for Atmospheres (GLA) by assimilation of the scatterometer winds in an atmospheric model. For the 10‐day period September 7–17 the intercomparison was extended to two further scatterometer wind fields: a 1000‐hPa assimilated wind field from the European Centre for Medium‐Range Weather Forecasts and a subjectively analyzed 19.5‐m‐height surface wind field from the Jet Propulsion Laboratory. On the global average, the modeled and observed wave heights agree reasonably well. Regional differences, however, can be large and sometimes exceed 40%. The errors are attributed mainly to deficiencies in the forcing wind fields. Low wind speeds are found to be overestimated and high wind speeds underestimated by the Seasat scatterometer algorithm. The friction velocities of the GLA model are found to be significantly underestimated in the high‐wind belt of the southern hemisphere. The analysis demonstrates the diagnostic advantages of applying a wave model for the quality assessment of satellite wind and wave data. A preliminary wave data assimilation scheme is presented in which the wave field is updated without changing the forcing wind field. A considerable improvement of the computed wave field is achieved, particularly in regions in which the wave energy is dominated by swell. However, a more general assimilation scheme including modifications of the wind field is needed to upgrade wind sea forecasts.

Light-shift-induced chaos in a nonlinear optical resonator.

The interaction of spin-1/2 atoms in an optical resonator with a near-resonant cw light field and an external static magnetic field gives rise to self-sustained spin precession. This entails a modulation on the transmitted light at roughly the Larmor frequency. We show that under suitable conditions this oscillation can become irregular. A detailed analysis reveals a deterministically chaotic process. Dimensions, entropies, and Lyapunov exponents are determined; cross-checks demonstrate their mutual consistency. To describe the observed dynamics, a three-dimensional model is presented that resembles the well-known Bloch equations. Numerical simulations compare well with the experimental results. Of all the nonlinear terms in the model, the one describing the light shift can be singled out as responsible for the chaotic behavior. This allows an intuitive understanding of the onset of chaos as a result of the interaction between spin precession and light shift.