James G. Mullen

On the impossibility of atomic commitment in multidatabase systems

Examines the problem of performing the atomic commitment of global transactions in multi-database system environments, where autonomous local database systems are integrated into a global database system. It is shown, that if the autonomy of the local database systems is preserved, it is impossible to perform atomic commitment in general, even under the assumption that there are no system failures. It is also shown that even when it is assumed that all local database systems use strict two phase locking (an assumption useful for performing global concurrency control), atomic commitment is impossible if even a single system failure can occur.<<ETX>>

MEASUREMENT OF THE DIFFUSION OF IRON IN GOLD BY MEANS OF THE MÖSSBAUER EFFECT

Iron diffusion in gold has been measured using the Mossbauer effect. Similar to earlier results on iron diffusion in copper, we find that the broadening of the Mossbauer line is approximately equal to ℏ/τ instead of 2ℏ/τ as predicted by the jump model of diffusion, where τ is the mean life for sitting in a specified lattice site. Since the broadening for both iron diffusion in gold and iron diffusion in copper is approximately a factor of two smaller than predicted theoretically, the results appear to be somewhat general. This lends support to the view that the relaxation of a specified ion out of a lattice site is not a simple exponential in time, as assumed in the theory, but is altered when the vacancy mechanism is responsible for diffusion.

Anharmonic contribution to the Debye-Waller factor for copper, silver, and lead.

Using high intensity ({similar_to}70 Ci) {sup 183}Ta Moessbauer sources, we have measured the elastic scattering fraction values, {ital scrF}, and the relative integrated scattering intensities for the (200), (400), (600), and (220) Bragg planes of copper and silver single crystals; and for the (200), (400), and (600) reflections of a lead single crystal. The experiments were done as a function of temperature from 82 K to a high temperature of 1086, 1211, and 507 K for Cu, Ag, and Pb, respectively. The {ital scrF} values were found by Moessbauer line-shape studies, and were used to correct the measured integrated intensities for thermal-diffuse scattering, so that accurate Debye-Waller factors (DWF`s) could be evaluated. The measured DWF`s for Cu, Ag, and Pb each have a significant anharmonic contribution at about 50% of the melting temperature ({ital T}{sub {ital m}}). Contrary to what Martin and O`Connor have reported for copper, we observed no {ital Q}{sup 4} contribution to the DWF within our experimental errors, which we estimate to be smaller than those reported by Martin and O`Connor.

Cold moving mice: A microfoil internal conversion electron detector for low and intermediate energy Mössbauer transitions

Abstract A microfoil internal conversion electron (MICE) detector is described which permits direct Doppler shifting of resonance radiation up to velocities of ± 20 cm/s, and gives large improvements in signal-to-background ratios for many Mossbauer isotopes, when compared with transmission geometry. The detector described has efficiency of nearly unity, and it allows for cooling the reciprocating microfoil module to 100 K, which improves signal-to-background substantially over room temperature operation. We give an analysis of the signal-to-background that can be expected for this MICE detector, and for a corresponding transmission experiment. In a table of neutron produced isotopes we find more than 10 cases which are favorable to the MICE approach as compared with the more conventional transmission geometry. The signal-to-background enhancement predicted for several Mossbauer isotopes is substantial for the MICE geometry compared to transmission geometry. Direct measurements of the Mossbauer conversion electron spectrum for the 46.5 and 99.1 keV transitions of 183 W and the 100.1 keV transition in 182 W are reported and compared with our analysis. In the case of 183 W (46.5 keV) we observe over 500% signal-to-background, and this experimental result agrees well with our analysis of the expected size of the effect. Satisfactory agreement is also found for the 99.1 keV 183 W and 100.1 keV 182 W spectra. Based on the analysis given it is possible to determine nuclear resonance cross sections and thereby infer internal conversion coefficients for the resonance transitions. Thus, we are able to determine the internal conversion coefficient for the 46.5 keV transition in 183 W to be α = 13 ± 3.

A gamma-ray diffraction instrument for high-intensity Mössbauer sources☆

A Mossbauer gamma-ray diffraction instrument has been developed which utilizes high intensity sources produced by neutron irradiation. Most of the early work has used 70 Ci, 5.1 d 183Ta sources produced by double neutron capture which yield 12 × 1010 photons/s for the 46.5 keV Mossbauer transition in 183W. A dewar is enclosed in the shielding cask which allows sources to be cooled to 77 K. Samples are located approximately midway between source and detector, which are separated by 155 cm. Collimators in front of the sample and detector commonly limit the beam to 3 mm wide by 25 mm high. A 27% minimum is seen in the velocity spectrum for the 46.5 keV photons scattered from the 200 Bragg reflection in LiF taken in transmission. Enriched, room temperature absorbers mounted on a rotor can be Doppler-shifted up to 17 meV. Q-space resolution of 0.01 A−1 is significantly better than that reported by other groups using Mossbauer scattering. When a microfoil internal conversion electron (MICE) detector is used, the instrument has the potential for directly measuring the energy transferred by the inelastically scattered photons, especially for low energy excitations in solids which require high energy resolution.

InterSQL: A Multidatabase Transaction Programming Language

This paper presents the InterSQL transaction programming language used in the InterBase-Star multidatabase system. InterBase-Star supports the atomic execution of transactions over heterogeneous, autonomous, and distributed component database systems. The component systems may use a variety of commitment methods, including ones recently developed specifically for multidatabase systems. Some of these new methods require the specification of semantic actions (e.g. compensating actions that semantically undo the effects of a subtransaction), and it is possible that multiple commitment methods may be used. Therefore, one requires the ability to specify which commitment methods may be used, and, for certain methods, semantic actions that are used to effect commitment. InterSQL is an object-oriented SQL-based transaction programming language that supports the specification of multidatabase transactions whose subtransactions may use various and multiple commitment methods.

InterBase: a multidatabase prototype systems

The computing environments of most organizations currently consist of distributed, heterogeneous, and autonomous hardware and software systems. Previously, these systems ran in isolation, supporting their individual applications. However, decreasing network costs made the connection of these distributed systems feasible, and it soon became evident that more complex applications, involving multiple systems, could be supported if the systems could cooperate with each other. The main obstacle to cooperation is local (system) autonomy. That is, it is generally not possible to modify pre-existing systems, and without modification, one generally can have only limited control over the systems.

Analytical representations of the Mössbauer recoilless fraction, Debye-Waller factors, lattice energies, and heat capacities

Simple analytical expansions are given for the recoilless fraction in Mössbauer spectroscopy, the Debye-Waller factor in X-ray scattering, and the lattice energy and heat capacity of solids. While this problem has been discussed in an earlier paper [1], computer technology has now advanced to the point that direct evaluations of the simple expansions of these quantities are useful for quick curve fitting to experimental data at any desired temperature, and these expansions are easier to evaluate than using graphs to estimate recoilless fractions and Debye temperatures. We compare this approach with a polynomial expansion in terms of Bernoulli numbers, which has only a limited domain of convergence. We explicitly evaluate the convergence of these Debye integral expansions as a function of the number of terms used and the time required.

Reservation Commitment and Its Use in Multidatabase Systems

This paper discusses a new atomic commitment protocol, called reservation commitment, and its implementation in multidatabase systems. The implementation discussed does not require component systems to provide a visible prepare-to-commit state (as does two phase commitment) and does not require component system modification. The reservation commitment protocol will work for cases not handled by the compensation approach and can be used to increase the number of cases where compensation will work. Finally, The reservation commitment protocol avoids the blocking of local read-only transaction that occurs in two phase commitment, and can take advantage of data and transaction semantics to decrease the level of blocking of local update transactions.

Implementing object support in the RAID distributed database system

The authors discuss the details of implementing O-Raid, an extension of the Raid system that supports complex data objects. Its data model combines properties of the relational model in Raid and the object model in C++. In particular, the authors describe the organization of objects on secondary storage, indexing of relations containing objects, processing of queries involving objects, and handling of method invocation. They also discuss how the components of the server-based organization in Raid are reused in the implementation of O-Raid.<<ETX>>