5 research outputs found
An enhanced dynamic replica creation and eviction mechanism in data grid federation environment
Get PDFData Grid Federation system is an infrastructure that connects several grid systems, which facilitates sharing of large amount of data, as well as storage and computing resources. The existing mechanisms on data replication focus on finding file values based on the number of files access in deciding which file to replicate, and place new replicas on locations that provide minimum read cost. DRCEM finds file values based on logical dependencies in deciding which file to replicate, and allocates new replicas on locations that provide minimum replica placement cost. This thesis presents an enhanced data replication strategy known as Dynamic Replica Creation and Eviction Mechanism (DRCEM) that utilizes the usage of data grid resources, by allocating appropriate replica sites around the federation. The proposed mechanism uses three schemes: 1) Dynamic Replica Evaluation and Creation Scheme, 2) Replica Placement Scheme, and 3) Dynamic Replica Eviction Scheme. DRCEM was evaluated using OptorSim network simulator based on four performance metrics: 1) Jobs Completion Times, 2) Effective Network Usage, 3) Storage Element Usage, and 4) Computing Element Usage. DRCEM outperforms ELALW and DRCM mechanisms by 30% and 26%, in terms of Jobs Completion Times. In addition, DRCEM consumes less storage compared to ELALW and DRCM by 42% and 40%. However, DRCEM shows lower performance compared to existing mechanisms regarding Computing Element Usage, due to additional computations of files logical dependencies. Results revealed better jobs completion times with lower resource consumption than existing approaches. This research produces three replication schemes embodied in one mechanism that enhances the performance of Data Grid Federation environment. This has contributed to the enhancement of the existing mechanism, which is capable of deciding to either create or evict more than one file during a particular time. Furthermore, files logical dependencies were integrated into the replica creation scheme to evaluate data files more accurately
A Dynamic Replica Creation and Eviction Mechanism based on Files Dependencies in a Federated Grid Environment
Get PDFFor quite a while, data replication has attracted the attention of many researchers in the field of data grid system, with a few researchers focusing on data replication in a federated data grid environment.The central goal of data replication mechanisms is to improve data locality, by creating more copies of the most popular files, and evicting unpopular files. In the conventional data grid systems, a common practice was to evaluate popular files based on economic approach, which evicts unpopular files based on least frequently or least recently used factor, to create space for incoming file replicas. However, this method tends to ignore the possible logical dependencies among st the replica files, which leads to the inappropriate evaluation of popular /unpopular files and consequently may result to the eviction of files with high logical dependencies on other files that may be needed later by other files or applications. As a resolution to this problem, a dynamic replica
creation and eviction mechanism (DRCEM) is
proposed by this research work, which considers
files logical dependencies, while evaluating popular or unpopular files and before evicting files from the syste
Grid Federation: Number of Jobs and File Size Effects on Jobs Time
Get PDFGrid federation is fast emerging as an alternative solution to the problems posed by the large data handling and computational needs of the existing numerous worldwide scientific projects. Efficient access to such extensively distributed data sets has become a fundamental challenge in grid computing. Creating and placing replicas to suitable sites, using data replication mechanisms can increase the system’s performance. Data Replication reduces data access time, ensures load balancing as well as narrows bandwidth consumption. In this paper, an enhanced data replication mechanism called EDR is proposed. EDR applies the principle of exponential growth/decay to both file size and file access history, based on the Latest Access Largest Weight (LALW) mechanism. The mechanism selects a popular file and determines an appropriate number of replicas as well as suitable grid sites for replication. It establishes the popularity of each file by associating a different weight to each historical data access record. Typically, recent data access record has a larger weight, which signifies that the record is more relevant to the current situation of data access. By varying the number of jobs as well as file sizes, the proposed EDR mechanism was simulated using file size and job completion time as the variable metrics. Optorsim simulator was used to evaluate the proposed mechanism alongside the existing Least Recently Used (LRU), and Least Frequently Used (LFU) Mechanisms. The simulation results showed that job completion time increases by the growth in both file size and number of jobs. EDR shows improved performance on the mean job completion time, compared to LRU and LFU mechanisms
A New Form of Authoritarianism? Rethinking Military Politics in Post-1999 Nigeria
No full textDespite the vast research that has been done on the Nigerian military, virtually all of these studies have failed to critically examine the accepted role of the military in the democratising phase. This is important because the relationship between the political elite and the military in post-military authoritarian states guarantees either democratic consolidation, or its reversal. In Nigeria, despite an appearance of significant progress in subordinating the military institution to democratic civilian authority, the military remains a crucial political actor in the polity. It appears that the military has yet to accept the core democratic principles of civilian oversight of the institution. This thesis, therefore, explores whether a new form of military authoritarianism is emerging in Nigeria, with the aim of understanding Nigeria’s military behaviour in a transitional phase, from prolonged military authoritarianism to democratisation. To examine this military behaviour, Alfred Stepan’s concept of military prerogatives that was used to understand the military’s behaviour in a transitional phase in Latin America is applied to Nigeria.
A crucial understanding of authoritarianism in Nigeria is initially discussed in this study using mainly document analysis strategy to examine whether multi-ethnic states, such as Nigeria, tend to have authoritarian systems. Six hypotheses form the core analysis of this thesis: first, that the military has retained significant military prerogatives; second, that retired military officers are gaining influential political and economic positions; third, autonomous military involvement in human rights abuses since 1999; and fourth, that civilian government oversight remains weak, and facilitates military authoritarianism. These hypotheses are primarily analysed using the elite interview technique. During the first half of 2011, the author conducted field research where serving and retired military officers were interviewed. The fifth hypothesis is that the military has intervened in politics post-1999. The examination of this hypothesis relies primarily on key security-related media reports (mostly newspaper editorials) on the military after 1999. The examination of the final hypothesis, that increases in military expenditures might facilitate a new form of military authoritarianism, relies primarily on descriptive statistical analysis. In addition, this study collated relevant historical materials that relate to the military, utilising national archival collections.
The empirical findings of this research did not identify a new form of military authoritarianism in Nigeria. The study, however, argues that the unrestricted institutional framework accorded the military has contributed significantly to authoritarian practices in the post-military era in Nigeria. This study discovered that there were similarities between the Brazilian and Nigerian militaries in regard to their military spending during their period in power. Both countries had lower defence budgets. Just as in Brazil, it appears that part of the reason the Nigerian military decided to relinquish power in 1999 had to do with its desire to gain a higher budget, something that was precluded in a military government struggling to retain a sense of legitimacy. The military needed a higher budget to modernise and re-professionalise its institution after more than a decade in power. This feature, which the Nigerian military shares with the Brazilian military, appears to justify the application to Nigeria of Alfred Stepan’s concept of military prerogatives.
DIAPH1-deficiency is associated with major t, nk and ılc defects in humans
Get PDFLoss of function mutations in Diaphanous related formin 1 (DIAPH1) are associated with seizures, cortical blindness, and microcephaly syndrome (SCBMS) and are recently linked to combined immunodeficiency. However, the extent of defects in T and innate lymphoid cells (ILCs) remain unexplored. Herein, we characterized the primary T, natural killer (NK) and helper ILCs of six patients carrying two novel loss of function mutation in DIAPH1 and Jurkat cells after DIAPH1 knockdown. Mutations were identified by whole exome sequencing. T-cell immunophenotyping, proliferation, migration, cytokine signaling, survival, and NK cell cytotoxicity were studied via flow cytometry-based assays, confocal microscopy, and real-time qPCR. CD4+ T cell proteome was analyzed by mass spectrometry. p.R351* and p.R322*variants led to a significant reduction in the DIAPH1 mRNA and protein levels. DIAPH1-deficient T cells showed proliferation, activation, as well as TCR-mediated signaling defects. DIAPH1-deficient PBMCs also displayed impaired transwell migration, defective STAT5 phosphorylation in response to IL-2, IL-7 and IL-15. In vitro generation/expansion of Treg cells from naïve T cells was significantly reduced. shRNA-mediated silencing of DIAPH1 in Jurkat cells reduced DIAPH1 protein level and inhibited T cell proliferation and IL-2/STAT5 axis. Additionally, NK cells from patients had diminished cytotoxic activity, function and IL-2/STAT5 axis. Lastly, DIAPH1-deficient patients’ peripheral blood contained dramatically reduced numbers of all helper ILC subsets. DIAPH1 deficiency results in major functional defects in T, NK cells and helper ILCs underlining the critical role of formin DIAPH1 in the biology of those cell subsets. Graphical Abstract: (Figure presented.). © The Author(s) 2024
