Timestamp Algorithms Research Articles

An Efficient Keywords Search in Temporal Social Networks

With the increasing of requirements from many aspects, various queries and analyses arise focusing on social network. Time is a common and necessary dimension in various types of social networks. Social networks with time information are called temporal social networks, in which time information can be the time when a user sends message to another user. Keywords search in temporal social networks consists of finding relationships between a group users that has a set of query labels and is valid within the query time interval. It provides assistance in social network analysis, classification of social network users, community detection, etc. However, the existing methods have limitations in solving temporal social network keyword search problems. We propose a basic algorithm, the discrete timestamp algorithm, with the intention of turning the problem into a traditional keyword search on social networks. We also propose an approximative algorithm based on the discrete timestamp algorithm, but it still suffers from the traditional algorithms’ low efficiency. To further improve the performance, we propose a new algorithm based on dynamic programming to solve the keyword search in temporal social network. The main idea is to extend a vertex into a solution by edge-growth operation and tree-merger operation. We also propose two powerful pruning techniques to reduce the intermediate results during the extension. Additionally, all of the algorithms we proposed are capable of handling a variety of ranking functions, and all of them can be made to conform to top-N keyword querying. The efficiency and effectiveness of the proposed algorithms are verified through extensive empirical studies.

Security Measures with Enhanced Behavior Processing and Footprint Algorithm against Sybil and Bogus Attacks in Vehicular Ad Hoc Network.

Vehicular ad hoc networks (VANETs) are created according to the principles of ad hoc mobile networks (MANETs), i.e., spontaneous creation of a wireless network for vehicle-to-vehicle (V2V) communication. Each vehicle in this network is treated as a node that is part of the mobile network. VANET turns all cooperating vehicles into a wireless router or node. This makes it possible to connect all cars within range to a stationary unit and create a wide network with a huge range. VANET is widely used for better traffic management, vehicle-to-vehicle communication, and road information provision. The VANET network is exposed to identity and information attacks, concealing or delaying data transmission, or information theft. Therefore, there are multiple types of attack, such as Sybil or bogus, that might harm the whole network infrastructure. The consequences of the mentioned two attacks could lead not only to the given infrastructure but could cause hammering people’s lives. In this paper, we analyze the ongoing methods for preserving Sybil and bogus attacks in a VANET network together with the authors’ methods: the Bogus & Sybil Trust Level & Timestamp (B&STL&T) algorithm and the Bogus & Sybil Enhanced Behavior Processing & Footprint (B&SEBP&F) algorithm. The first algorithm, the Bogus & Sybil Trust Level & Timestamp (B&STL&T) algorithm was improved into the Bogus & Sybil Enhanced Behavior Processing & Footprint (B&SEBP&F), presented in the paper. The proposed methods were tested with multiple scenarios using different variations of bogus and Sybil attack and various attacker–victim node number ratios. During analysis, it was observed that detection of all attackers in the network was reduced by approximately 30% in comparison to previous work and that of other cited authors.

Secure File Sharing System in Cloud Using AES and Time Stamping Algorithms

In recent days, the growth of digital data has been increased explosively due to data-intensive applications like healthcare, education and electronic commerce. Due to the huge volume of data created and the utilization of data in emerging applications, a local storage device has to be deployed. Cloud storage services allow both the individuals and commercial users for the outsourcing of data to the cloud server and to access the data remotely with the help of the internet, so the demand for cloud storage has been raised. However, one of the critical problems of cloud data storage is security. Some researchers have used third party auditor for verifying the data stored in the cloud. This paper introduces a novel method for cloud storage and for protecting the organizations’ data. The proposed system strengthens the level of authentication with the help of AES and time-stamping algorithms. The experimental results demonstrate the efficiency of the proposed method when auditing the shared data integrity

Low-Power, Bio-Inspired Time-Stamp-Based 2-D Optic Flow Sensor for Artificial Compound Eyes of Micro Air Vehicles

We report a low-power, bio-inspired mixed-signal 2-D optic flow sensor to realize artificial compound eyes, which can provide a wide field of view (FoV) sensing capability for autonomous navigation of micro-air-vehicles (MAVs). Inspired by insect vision, a 2-D time-stamp algorithm has been developed to scale the number of deployable sensors at low power. The fabricated sensor estimates 16-b 2-D optic flows of maximum 1.96 rad/s with FoV of 60° from the integrated mixed-signal algorithm core, which consumes only 243.3 pJ/pixel or $\sim 30~\mu \text{W}$ at 120 fps. In addition, the peripheral circuits for modular design have been integrated on chip to provide optic flow data compression, wide-field integration (WFI), and serial peripheral interface (SPI). More than 25 sensors can be connected in a single SPI bus and transmit the full resolution optic flows. The fabricated prototype sensor supports full resolution 2-D optic flows from an array of $64\times 64$ pixels at 120 fps through a 3 MB/s SPI bus (4 wires total).

DProf: distributed profiler with strong guarantees

Performance analysis of a distributed system is typically achieved by collecting profiles whose underlying events are timestamped with unsynchronized clocks of multiple machines in the system. To allow comparison of timestamps taken at different machines, several timestamp synchronization algorithms have been developed. However, the inaccuracies associated with these algorithms can lead to inaccuracies in the final results of performance analysis. To address this problem, in this paper, we develop a system for constructing distributed performance profiles called DProf. At the core of DProf is a new timestamp synchronization algorithm, FreeZer, that tightly bounds the inaccuracy in a converted timestamp to a time interval. This not only allows timestamps from different machines to be compared, it also enables maintaining strong guarantees throughout the comparison which can be carefully transformed into guarantees for analysis results. To demonstrate the utility of DProf, we use it to implement dCSP and dCOZ that are accuracy bounded distributed versions of Context Sensitive Profiles and Causal Profiles developed for shared memory systems. While dCSP enables user to ascertain existence of a performance bottleneck, dCOZ estimates the expected performance benefit from eliminating that bottleneck. Experiments with three distributed applications on a cluster of heterogeneous machines validate that inferences via dCSP and dCOZ are highly accurate. Moreover, if FreeZer is replaced by two existing timestamp algorithms (linear regression & convex hull), the inferences provided by dCSP and dCOZ are severely degraded.

TS-MUWSN: Time Synchronization for Mobile Underwater Sensor Networks

Time synchronization is an important, yet challenging, problem in underwater sensor networks (UWSNs). This challenge can be attributed to: 1) messaging timestamping; 2) node mobility; and 3) Doppler scale effect. To mitigate these problems, we present an acoustic-based time-synchronization algorithm for UWSN, where we compare several message time-stamping algorithms in addition to different Doppler scale estimators. A synchronization system is based on a bidirectional message exchange between a reference node and a slave one, which has to be synchronized. Therefore, we take as reference the DA-Sync-like protocol (Liu et al., 2014), which takes into account node's movement by using first-order kinematic equations, which refine Doppler scale factor estimation accuracy, and result in better synchronization performance. In our study, we propose to modify both time-stamping and Doppler scale estimation procedures. Besides simulation, we also perform real tests in controlled underwater communication in a water test tank and a shallow-water test in the Mediterranean Sea.

Optimal lower bounds for projective list update algorithms

The list update problem is a classical online problem, with an optimal competitive ratio that is still open, known to be somewhere between 1.5 and 1.6. An algorithm with competitive ratio 1.6, the smallest known to date, is COMB, a randomized combination of BIT and the TIMESTAMP algorithm TS. This and almost all other list update algorithms, like MTF, are projective in the sense that they can be defined by looking only at any pair of list items at a time. Projectivity (also known as “list factoring”) simplifies both the description of the algorithm and its analysis, and so far seems to be the only way to define a good online algorithm for lists of arbitrary length. In this article, we characterize all projective list update algorithms and show that their competitive ratio is never smaller than 1.6 in the partial cost model. Therefore, COMB is a best possible projective algorithm in this model.

A compact digital time differential perturbed angular correlation-spectrometer using field programmable gate arrays and various timestamp algorithms

A user-friendly fully digital time differential perturbed angular correlation (TDPAC)-spectrometer with six detectors and fast digitizers using field programmable gate arrays (FPGA) is described and performance data are given. The new spectrometer has an online data analysis feature, a compact size, and a time resolution such as conventional analog spectrometers. Its calculation intensive part was implemented inside the digitizer. This gives the possibility to change parameters (energy windows, constant fraction trigger delay) and see their influence immediately in the γ-γ correlation diagrams. Tests were performed which showed that the time resolution using a (60)Co source with energy window set at 1.17 MeV and 1.33 MeV is 265 ps with LaBr(3)(Ce) scintillators and 254 ps with BaF(2) scintillators. A true constant fraction algorithm turned out to be slightly better than the constant fraction of amplitude method. The spectrometer performance was tested with a TDPAC measurement using a (44)Ti in rutile source and a positron lifetime measurement using (22)Na. The maximum possible data rate of the spectrometer is 1.1 × 10(6) γ quanta per detector and second.

Real time digital signal processing implementation for an APD-based PET scanner with phoswich detectors

Recent progress in advanced digital signal processing provides an opportunity to expand the computation power required for real time extraction of event characteristics in avalanche photodiode (APD)-based Positron Emission Tomography (PET) scanners. These developments are made possible by a highly parallel data acquisition (DAQ) system based on an integrated analog front-end and a high-speed fully digital signal processing section that directly samples the output of each preamplifier with a free-running, off-the-shelf, 45-MHz analog-to-digital converter that feeds the sampled data into a field programmable gate array (FPGA) VirtexII PRO from Xilinx. This FPGA features /spl sim/ 31 000 logic cells and two PowerPC processors, which allows up to 64 channels to be processed simultaneously. Each channel has its own digital signal processing chain including a trigger, a baseline restorer and a timestamp algorithm. Various timestamp algorithms have been tested so far, achieving a coincidence timing resolution of 3.2-ns full-width at half-maximum (FWHM) for APD coupled to Lutetium Oxyorthosilicate (APD-LSO) and 11.4-ns FWHM for APD coupled to Bismuth Germanium Oxide (APD-BGO) detectors, respectively. Channels are then multiplexed into a DSP processor from Texas Instruments for crystal identification by an ARMAX recursive algorithm borrowed from identification and vector quantization theory. The system can sustain an event rate of 10 000 events/s/channel without electronic dead time.

Time stamp algorithms for runtime parallelization of DOACROSS loops with dynamic dependences

This paper presents a time stamp algorithm for runtime parallelization of general DOACROSS loops that have indirect access patterns. The algorithm follows the INSPECTOR/EXECUTOR scheme and exploits parallelism at a fine-grained memory reference level. It features a parallel inspector and improves upon previous algorithms of the same generality by exploiting parallelism among consecutive reads of the same memory element. Two variants of the algorithm are considered: One allows partially concurrent reads (PCR) and the other allows fully concurrent reads (FCR). Analyses of their time complexities derive a necessary condition with respect to the iteration workload for runtime parallelization. Experimental results for a Gaussian elimination loop, as well as an extensive set of synthetic loops on a 12-way SMP server, show that the time stamp algorithms outperform iteration-level parallelization techniques in most test cases and gain speedups over sequential execution for loops that have heavy iteration workloads. The PCR algorithm performs best because it makes a better trade-off between maximizing the parallelism and minimizing the analysis overhead. For loops with light or unknown iteration loads, an alternative speculative runtime parallelization technique is preferred.

Improved Randomized On-Line Algorithms for the List Update Problem

The best randomized on-line algorithms known so far for the list update problem achieve a competitiveness of $\sqrt{3} \approx 1.73$. In this paper we present a new family of randomized on-line algorithms that beat this competitive ratio. Our improved algorithms are called TIMESTAMP algorithms and achieve a competitiveness of $\max\{2-p, 1+p(2-p)\}$, for any real number $p\in[0,1]$. Setting $p = (3-\sqrt{5})/2$, we obtain a $\phi$-competitive algorithm, where $\phi = (1+\sqrt{5})/2\approx 1.62$ is the golden ratio. TIMESTAMP algorithms coordinate the movements of items using some information on past requests. We can reduce the required information at the expense of increasing the competitive ratio. We present a very simple version of the TIMESTAMP algorithms that is \mbox{$1.68$-competitive}. The family of TIME\-STAMP algorithms also includes a new deterministic 2-competitive on-line algorithm that is different from the MOVE-TO-FRONT rule.

Analysis of impact of network delay on multiversion conservative timestamp algorithms in DDBS

In a distributed environment, users access databases in remote sites via a communication network. The randomness of the network delay may cause operations to arrive at the remote sites out of sequence. Multiversion conservative timestamp algorithms can be used to schedule the operations to maintain the consistency of the databases. We model the algorithms as queueing systems with partial order resequencing constraints, where the resequencing constraints vary as the number of versions in the algorithms. Under the assumption of an iid network delay, the distributions of the response time of operations and the buffer occupancy in the resequencing buffer are derived analytically for the algorithms with version number one to infinity. The impact of the network delay on the performance of the DDBS is investigated. It is found that the variance of the network delay has significant effect on the system performance.

A combined BIT and TIMESTAMP algorithm for the list update problem

We present a randomized on-line algorithm for the list update problem which achieves a competitive factor of 1.6, the best known so far. The algorithm makes an initial random choice between two known algorithms that have different worst-case request sequences. The first is the BIT algorithm that, for each item in the list, alternates between moving it to the front of the list and leaving it at its place after it has been requested. The second is a TIMESTAMP algorithm that moves an item in front of less often requested items within the list.

Distributed timestamp generation in planar lattice networks

Timestamps are considered for distributed environments in which information flow is restricted to one direction through a planar lattice imposed on a network. For applications in such networks, existing timestamping algorithms require extension and modification. For example, in secure environments, typical timestamps provide a potential signaling channel between incomparable levels. In hierarchical databases, typical timestamps cause peripheral sites to unnecessarily affect the behavior at main sites. Algorithms are presented by which a network node may generate and compare timestamps using timestamp components maintained at dominated nodes in the network. The comparison relation is shown to be acyclic for timestamps produced by the generation algorithm. We discuss ways to safely relax the requirement that the network be a lattice. By example, we show how to modify a simple nonplanar lattice so that the generation algorithm can be applied. Uses of the timestamp generation algorithm in the motivating applications are outlined.

An analysis of the effect of multiversions on the performance of timestamp algorithms

The performance of a multiversion conservative timestamp algorithm is evaluated by analyzing the response time of operations in a distributed database system. The random communication delay in the transmission channels of a long-haul network supporting the distributed database system causes transmitted operations to be received out of order. According to rules that are dependent on the number of versions, the scheduler reorders the operations to preserve the consistency of the database. Operations encounter extra delay in the process of reordering. The system is modeled by a queuing network. Response-time distributions are obtained analytically. Numerical results are presented to show the effect of the number of versions on the performance. >