Investigation of the robustness of star graph networks

The star interconnection network has been known as an attractive alternative to n-cube for interconnecting a large number of processors. It possesses many nice properties, such as vertex/edge symmetry, recursiveness, sublogarithmic degree and diameter, and maximal fault tolerance, which are all desirable when building an interconnection topology for a parallel and distributed system. Investigation of the robustness of the star network architecture is essential since the star network has the potential of use in critical applications. In this study, three different reliability measures are proposed to investigate the robustness of the star network. First, a constrained two-terminal reliability measure referred to as Distance Reliability (DR) between the source node u and the destination node I with the shortest distance, in an n-dimensional star network, Sn, is introduced to assess the robustness of the star network. A combinatorial analysis on DR especially for u having a single cycle is performed under different failure models (node, link, combined node/link failure). Lower bounds on the special case of the DR: antipode reliability, are derived, compared with n-cube, and shown to be more fault-tolerant than n-cube. The degradation of a container in a Sn having at least one operational optimal path between u and I is also examined to measure the system effectiveness in the presence of failures under different failure models. The values of MTTF to each transition state are calculated and compared with similar size containers in n-cube. Meanwhile, an upper bound under the probability fault model and an approximation under the fixed partitioning approach on the ( n-1)-star reliability are derived, and proved to be similarly accurate and close to the simulations results. Conservative comparisons between similar size star networks and n-cubes show that the star network is more robust than n-cube in terms of ( n-1)-network reliability

Instrumentation of YSZ oxygen sensor calibration in lead-bismuth eutectic

Although liquid lead-bismuth eutectic (LBE) is a good candidate for the coolant in the subcritical transmutation blanket, it is also known to be very corrosive to stainless steel, the material of the carrying tubes and the containers. Such a corrosion problem can be prevented by producing and maintaining a protective oxide layer on the exposed surface of stainless steel. Proper formation of the oxide layer critically depends on the accurate measurement and control of the oxygen concentration (tens of ppb levels) in the liquid LBE. An Oxygen Sensor Calibration/Measurement Apparatus is designed and built to deliberately calibrate the Yttria Stabilized Zirconia (YSZ) oxygen sensor. A detailed description of this system with main components and their functions is presented. Some calibration results have been done and is presented and analyzed here. Analysis on the characteristics of this YSZ sensor and the effectiveness of the calibration apparatus are also discussed

Optimizing Sparse Matrix-Matrix Multiplication on a Heterogeneous CPU-GPU Platform

Sparse Matrix-Matrix multiplication (SpMM) is a fundamental operation over irregular data, which is widely used in graph algorithms, such as finding minimum spanning trees and shortest paths. In this work, we present a hybrid CPU and GPU-based parallel SpMM algorithm to improve the performance of SpMM. First, we improve data locality by element-wise multiplication. Second, we utilize the ordered property of row indices for partial sorting instead of full sorting of all triples according to row and column indices. Finally, through a hybrid CPU-GPU approach using two level pipelining technique, our algorithm is able to better exploit a heterogeneous system. Compared with the state-of-the-art SpMM methods in cuSPARSE and CUSP libraries, our approach achieves an average of 1.6x and 2.9x speedup separately on the nine representative matrices from University of Florida sparse matrix collection

Promotion of antitumor activity of CIK cells by targeting the NKG2D axis

CIK cells are an ex vivo expanded heterogeneous cell population with an enriched NK-T phenotype (CD3+CD56+). Due to the convenient and inexpensive expansion capability, together with low incidence of GVHD in allogeneic cancer patients, CIK cells are a promising candidate for immunotherapy. It is well known that NKG2D plays an important role in CIK cell-mediated antitumor activity, thus upregulation of NKG2D ligands on tumor cells might elevate the immune response of CIK to these tumor targets. However, it still remains unclear whether NKG2D engagement alone is sufficient or if it requires additional co-stimulatory signals (e.g. 2B4) to activate CIK cells. In order to address these issues and assess the in vitro cytotoxicity of CIK cells in a more accurate and efficient way, we first established an improved flow cytometric cytotoxicity assay based on prior studies. Instead of using calibration beads, a fixed acquisition time can be utilized to standardize the flow cyometric assay with similar efficiency but higher stability. Furthermore, the sample acquisition can be shortened to 15 sec for each tube, thereby making this methodology more cost-effective and efficient. Next, we investigated the individual and cumulative contribution of NKG2D and 2B4 to the activation of CIK cells. Unlike resting NK cells, we found NKG2D engagement alone is sufficient to activate CIK cells, inducing deganulation, IFN-γ secretion and LFA-1 activation, while 2B4 alone failed to elicit these activities and only provides synergistic effect on LFA-1 activation with NKG2D. Unexpectedly, NKG2D was unable to costimulate CD3 in the cytotoxicity of CIK cells. These data indicate the divergences in the role of NKG2D between CIK cells and NK (or T) cells. Nevertheless, we demonstrate that NKG2D alone suffices to activate CIK cells, thus strenghthening the idea of targeting the NKG2D axis may promote the antitumor efficacy of CIK cells. To this end, we further investigated whether the upregulaton of NKG2D ligands on tumor targets can incease the sensitivity of CIK cells. By using an anti-MICA α3 domain monoclonal antibody (7C6 mAb), which was shown to specifically inhibit the MICA shedding and stabilize its surface density on tumor cells (Hela and MDA-MB-231), we found that the CIK cell-mediated antitumor activities (including cytotoxicity, degranulation, IFN-γ secretion) were substantially enhanced. The effect was mostly modulated through NKG2D axis as NKG2D blocking offset the 7C6-driven enhancement in these activities. Collectively, the findings presented in this thesis demonstrate that targeting the NKG2D axis is a promissing approach to improve the antimumor activity of CIK cells, suggesting that the combinatory treatment of CIK cells with other therapeutic modalities which are able to induce or upregulate NKG2D ligands holds great potential to improve the clincial response of cancer patients