Timestamp Technique Research Articles

Probing nanosecond protein motions of calmodulin by single-molecule fluorescence anisotropy

We report a single-molecule fluorescence anisotropy study of calmodulin, a regulatory protein for calcium-dependent cell signaling. Calmodulin in this study contains a site-specifically inserted tetra-cysteine motif that reacted with FlAsH, a biarsenic fluorescein derivative that can be rotationally locked to the host protein. A photon time-stamping technique was employed that combined the capability for both subnanosecond time resolution of time-correlated single photon counting and single-molecule time trajectory recording. The study provided direct characterization of the nanosecond motions of calmodulin tethered to a biologically compatible surface under physiological buffer solution. The unique technical approaches are applicable to single-molecule study of protein conformational dynamics and protein–protein interactions at a wide range of time scales and without the signal convolution of probe-dye molecular motions.

A positive acknowledgment protocol for causal broadcasting

Causal broadcasting has been introduced to reduce the asynchrony of communication channels inside groups of processes. It states that if two broadcast messages are causally related by the happened-before relation, these messages are delivered in their sending order to each process of the group. Even though protocols implementing causal broadcasting do not add control messages, they suffer from the typical pitfall of the timestamping technique: To ensure causal ordering, application messages have to piggyback a vector time of counters whose range of variation is unbounded. In this paper, we investigate such a range and define the concept of causal window of a process in which all counters of a vector time of a just arrived message at that process fall. We prove that, by using a causal broadcasting (one-to-all) protocol that follows a positive acknowledgment method, the width of the causal window of each process is limited. This allows a modulo k implementation of vector times when considering k greater than the width of the causal window of each process. The protocol is applicable to data link or transport layers using acknowledge messages to ensure reliable transfer of data. The paper also proposes two variants of the protocol based on causal windows. Both of them increase the concurrency of the protocol at the expense of wider causal windows.

Non-repudiation: Constituting evidence and proof in digital cooperation

In digital cooperation, mechanisms and services have to be provided to account for actions and information to entities. Digital signatures are regarded as a means of establishing accountability, the property that ensures that the actions of an entity may be traced uniquely to that entity. However, to constitute proof of origin, submission, delivery and receipt, digital signature techniques have to be supported by certification, time stamping and notarisation techniques and services. The techniques providing proofs are called non-repudiation techniques. Working Group 2 of ISO/IEC JTC1/SC27 (Security Techniques) is concerned with the standardization of security mechanisms and algorithms such as digital signatures. A new work item has been defined on non-repudiation techniques using asymmetric (digital signatures) as well as symmetric cryptographic techniques.

Performance comparison of database concurrency control mechanisms based on two-phase locking, timestamping and mixed approach

Many techniques have been proposed for managing concurrent execution of transactions in database systems. There are two well-known categories: one uses locks and the other uses timestamps. The performance of seven different concurrency control algorithms belonging to these two categories have been investigated with the help of detailed and realistic simulation models so that a comparative evaluation of their performance can be done. These include the performance of four different locking techniques, the basic timestamp technique and wound-wait and wait-die systems. We have evaluated the effect of deadlocks, read : write ratio, cascade rollback, degree of concurrency, transaction-size mixes, transaction wait time and transaction blockings on the overall performance of these algorithms. We show that cascade rollbacks, contrary to our expectation, do not affect throughput significantly, since these rollbacks do not occur very frequently and their average degree is always small. Deadlocks occur rarely and the degree of cycles is never very high. The effect of read : write ratios does not extend to higher transaction arrival rates and the effect of transaction waittime on the throughput is not so severe. We also give some guidelines for selecting the most suitable concurrency control mechanism for a particular type of workload.