Transaction decomposition using transaction semantics

Serializability has been widely accepted as the correctness criterion for databases subject to concurrent access. However, in a number of the newer and most challenging application areas, serializable execution may not be feasible.

? Serializable execution is generally implemented using a two-phase locking algorithm that locks items in the database to delay transactions that are in danger of performing in a non-serializable fashion. Such delays are unacceptable in high performance database systems that must process hundreds, and perhaps thousands, of transactions per second and in systems supporting long-running transactions.

? In systems in which data is distributed across a federated database, a global transaction is decomposed into a set of local subtransactions executed at a subset of the sites. Serializable execution in such systems not only incurs a performance penalty, but also requires the component systems to cooperate (for example in a two phase commit protocol), with a resulting loss of site autonomy. In many applications, the component systems either can not or will not agree to the required cooperation.

A number of models have recently been proposed in which transactions are decomposed into smaller, atomic, interleavable steps. These models have the potential for improving performance since locks are released at the end of each step. Models of distributed transactions have also been proposed with the similarity that subtransactions correspond to steps. In most of this work serializability is no longer guaranteed. In this paper we propose a new, application-oriented, correctness criterion that utilizes transaction semantics. We treat transactions as programs whose semantics can be analyzed at design time. The effect of each transaction is specified using pre- and postconditions, and any schedule that preserves these conditions is permissible. Such schedules can produce database states that could not be reached by any serial execution. In addressing the issue of performance, we use transaction semantics to decompose transactions into steps and describe a concurrency control that controls step interleaving in such a way that assertions are preserved. The same model can be used to study the interleaving of subtransactions of concurrent distributed transactions.     

Robust H∞ stabilization via parametrized Lyapunovbounds

The parametrized Lyapunov bounding technique of Haddad and Bernstein (1991, 1993, 1995) is extended to include an H_∞ -disturbance attenuation constraint. The results presented in this paper provide a framework for designing fixed-order (i.e., full- and reduced-order) controllers that guarantee robust H₂ and H_∞ performance in the presence of structured constant real parameter variations in the state space model     

Semilinear Duhem model for rate-independent and rate-dependent hysteresis

The classical Duhem model provides a finite-dimensional differential model of hysteresis. In this paper, we consider rate-independent and rate-dependent semilinear Duhem models with provable properties. The vector field is given by the product of a function of the input rate and linear dynamics. If the input rate function is positively homogeneous, then the resulting input-output map of the model is rate independent, yielding persistent nontrivial input-output closed curve (that is, hysteresis) at arbitrarily low input frequency. If the input rate function is not positively homogeneous, the input-output map is rate dependent and can be approximated by a rate-independent model for low frequency inputs. Sufficient conditions for convergence to a limiting input-output map are developed for rate-independent and rate-dependent models. Finally, the reversal behavior and orientation of the rate-independent model are discussed.     

Nonulcerating bacterial keratitis associated with soft and rigid contact lens wear

Most patients in acute myocardial infarction (AMI) undergo emergent coronary angiography (CAG). However, when to analyze lipoprotein profiles in AMI is not clear. To determine whether lipoprotein profiles change during catheterization, we measured serum lipid and apolipoprotein concentrations in 65 patients (51 men and 14 women) before and after catheterization. Heparin was injected at 50 units/kg for CAG and 200 units/kg for percutaneous transluminal coronary angioplasty (PTCA). We found that cholesterol and triglyceride decreased by 9.4% (P < 0.001) and 53.1% (P < 0.001), respectively, after catheterization. Apolipoproteins also decreased significantly. Variables decreased two to five times more after PTCA than after CAG. Lipoprotein lipase mass was higher after PTCA (267.8 +/- 135.3 micrograms/L) than after CAG (93.3 +/- 48.4 micrograms/L; P < 0.05). In conclusion, lipoprotein profiles change during catheterization. We recommend avoiding analysis of lipoprotein profiles after emergent CAG in AMI.     

Concurrent task demands and individual differences in the architecture of reading: Discriminating artifacts from real McCoys.

K. R. Paap and R. W. Noel (1991) observed a striking effect in which low-frequency exception words were pronounced faster under a larger memory load although other types of words slowed down. This effect strongly favored dual-route models of pronunciation. S. E. Bernstein and T. H. Carr (1996) reported that only certain selected readers produced Paap and Noel's effect, suggesting individual differences in reading-system architecture. P. M. Pexman and S. J. Lupker (1998) criticized Bernstein and Carr's finding as artifactual and failed to replicate it with a different way of selecting readers. They also failed to support an alternative individual-difference hypothesis of their own. In the current article, the authors developed a new approach to identifying individual differences and applied the approach to a variety of data. They found little evidence of systematic individual differences in the occurrence of Paap and Noel's effect, and indeed, they found little evidence that the effect could be replicated at all. Therefore, they gave up. (PsycINFO Database Record (c) 2010 APA, all rights reserved)