5,382 research outputs found
Effect of base–acid properties of the mixtures of water with methanol on the solution enthalpy of selected cyclic ethers in this mixture at 298.15 K
The enthalpies of solution of cyclic ethers: 1,4-
dioxane, 12-crown-4 and 18-crown-6 in the mixture of
water and methanol have been measured within the whole
mole fraction range at T = 298.15 K. Based on the obtained
data, the effect of base–acid properties of water–
methanol mixtures on the solution enthalpy of cyclic ethers
in these mixtures has been analyzed. The solution enthalpy
of cyclic ethers depends on acid properties of water–
methanol mixtures in the range of high and medium water
contents in the mixture. Based on the analysis performed, it
can be assumed that in the mixtures of high methanol
contents, cyclic ethe
Traquest model : a novel model for ACID concurrent computations
Atomicity, consistency, isolation and durability are essential properties of many distributed systems. They are often abbreviated as the ACID properties. Ensuring ACID comes with a price: it requires extra computing and network capacity to ensure that the atomic operations are done perfectly, or they are rolled back. When we have higher requirements on performance, we need to give up the ACID properties entirely or settle for eventual consistency. Since the ambiguity of the order of the events, such algorithms can get very complicated since they have to be prepared for any possible contingencies. Traquest model is an attempt for creating a general concurrency model that can bring the ACID properties without sacrificing a too significant amount of performance
Atomicity Implementation in E-Commerce Systems
Distributed databases with high performance and availability do not have the traditional ACID properties (Atomicity, Consistency, Isolation and Durability) because long duration locks will reduce the availability and the write performance. The problems of the missing ACID properties may be avoided by using approximated ACID properties, i.e. from an application point of view; the system should function as if all the traditional ACID properties had been implemented. The distributed approximated atomicity property manages the workflow of a transaction in such a way that either all the updates of the global transaction are executed (sooner or later) or all the updates of the global transaction are removed/compensated. In this paper, we will describe a flexible algorithm for implementing distributed approximated atomicity. Frank and Zahle [1] have described how to implement the other global approximated ACID properties.
We will illustrate our algorithm with E-commerce examples. If one of the partaking subsystems fails in a system for E-commerce, the approximated atomicity property will ensure that when an order is accepted, the payment and stock levels are managed automatically in the locations of the partaking banks and product stocks. Even logistics and/or production may be managed by using approximated atomicity.
We have cooperated with one of the major ERP (Enterprise Resource Planning) software companies in designing a distributed version of the ERP system with local autonomous databases in the different sales and stock locations
Transactional Support for Visual Instance Search
International audienceThis article addresses the issue of dynamicity and durability for scalable indexing of very large and rapidly growing collections of local features for visual instance retrieval. By extending the NV-tree, a scalable disk-based high-dimensional index, we show how to implement the ACID properties of transactions which ensure both dynamicity and durability. We present a detailed performance evaluation of the transactional NV-tree, showing that the insertion throughput is excellent despite the effort to enforce the ACID properties
METHOD FOR THE PRODUCTION OF HIGH SATURATED, LOW POLYUNSATURATED SOYBEAN OIL
Methods of genetically modifying soybean plants to alter the fatty acid properties of the oil are described
A Realistic Model under which the Genetic Code is Optimal
The genetic code has a high level of error robustness. Using values of
hydrophobicity scales as a proxy for amino acid character, and the Mean Square
measure as a function quantifying error robustness, a value can be obtained for
a genetic code which reflects the error robustness of that code. By comparing
this value with a distribution of values belonging to codes generated by random
permutations of amino acid assignments, the level of error robustness of a
genetic code can be quantified. We present a calculation in which the standard
genetic code is shown to be optimal. We obtain this result by (1) using
recently updated values of polar requirement as input; (2) fixing seven
assignments (Ile, Trp, His, Phe, Tyr, Arg, and Leu) based on aptamer
considerations; and (3) using known biosynthetic relations of the 20 amino
acids. This last point is reflected in an approach of subdivision (restricting
the random reallocation of assignments to amino acid subgroups, the set of 20
being divided in four such subgroups). The three approaches to explain
robustness of the code (specific selection for robustness, amino acid-RNA
interactions leading to assignments, or a slow growth process of assignment
patterns) are reexamined in light of our findings. We offer a comprehensive
hypothesis, stressing the importance of biosynthetic relations, with the code
evolving from an early stage with just glycine and alanine, via intermediate
stages, towards 64 codons carrying todays meaning.Comment: 22 pages, 3 figures, 4 tables Journal of Molecular Evolution, July
201
The Genetic Code as a Periodic Table: Algebraic Aspects
The systematics of indices of physico-chemical properties of codons and amino
acids across the genetic code are examined. Using a simple numerical labelling
scheme for nucleic acid bases, data can be fitted as low-order polynomials of
the 6 coordinates in the 64-dimensional codon weight space. The work confirms
and extends recent studies by Siemion of amino acid conformational parameters.
The connections between the present work, and recent studies of the genetic
code structure using dynamical symmetry algebras, are pointed out.Comment: 26 pages Latex, 10 figures (4 ps, 6 Tex). Refereed version, small
changes to discussion (conclusion unaltered). Minor alterations to format of
figures and tables. To appear in BioSystem
TRANSACTION DESIGN FOR DATABASES WITH HIGH PERFORMANCE AND AVAILABILITY
When many concurrent transactions like ERP and E-commerce orders want to update the same stock records, long duration locking may reduce the availability of the locked data. Therefore, transactions are often designed without analyzing the consequences of loosing the traditional ACID (Atomicity, Consistency, Isolation and Durability) properties. In this paper, we will analyze how low isolation levels, optimistic concurrency control, short duration locks, and countermeasures against isolation anomalies can be used to design transactions for databases with high performance and availability. Long duration locks are defined as locks that are held until a transaction has been committed, Le. the data of a record is locked from the first read to the last update of any data used by the transaction. This will decrease the availability of locked data for concurrent transactions, and, therefore, optimistic concurrency control and low isolation levels are often used. However, in systems with relatively many updates like ERP-systems and E-commerce systems, low isolation levels cannot solve the availability problem as all update locks must be exclusive. In such situations, we will recommend the use of short duration locks. Short duration locks are local locks that are released as soon as possible, Le. data will for example not be locked across a dialog with the user. Normally, databases where only short duration locks are used do not have the traditional ACID properties as at least the isolation property is missing when locks are not hold across a dialog with the user. The problems caused by the missing ACID properties may be managed by using approximated ACID properties, i.e. from an application point of view the system should function as if all the traditional ACID properties had been implemented
- …