Two-layer Locally Repairable Codes for Distributed Storage Systems

In this paper, we propose locally repairable codes (LRCs) with optimal minimum distance for distributed storage systems (DSS). A two-layer encoding structure is employed to ensure data reconstruction and the designated repair locality. The data is first encoded in the first layer by any existing maximum distance separable (MDS) codes, and then the encoded symbols are divided into non-overlapping groups and encoded by an MDS array code in the second layer. The encoding in the second layer provides enough redundancy for local repair, while the overall code performs recovery of the data based on redundancy from both layers. Our codes can be constructed over a finite field with size growing linearly with the total number of nodes in the DSS, and facilitate efficient degraded reads.Comment: This paper has been withdrawn by the author due to inaccuracy of Claim

Computations of fully nonlinear three-dimensional wave-body interactions

Thesis (Ph. D. in Ocean Engineering)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2010.Cataloged from PDF version of thesis.Includes bibliographical references.Nonlinear effects in hydrodynamics of wave-body interaction problems become critically important when large-amplitude body motions and/or extreme surface waves are involved. Accurate prediction and understanding of these fully nonlinear effects are still challenges in the design of surface ships and marine structures, owing to the complexity of the hydrodynamic problem itself and limited computational facilities. This research is focused on: (i) development of a highly efficient numerical scheme for the computation of fully-nonlinear three-dimensional wave-body interactions; and (ii) investigation of several highly nonlinear wave-body interaction problems for understanding associated key nonlinear effects. A highly efficient high-order boundary element method is developed based on the framework of the quadratic boundary element method (QBEM) for the boundary integral equation and using the pre-corrected fast Fourier transform (PFFT) algorithm to accelerate the evaluation of far-field influences of source and/or normal dipole distributions on boundary elements. The resulting numerical scheme reduces the computational effort of solving the boundary-value problem from O(N 2 ~3) (with the traditional boundary element methods) to O(N ln N) where N represents the total number of boundary unknowns. Combining with the mixed-Eulerian-Lagrangian (MEL) approach for nonlinear free surface tracking, we develop an efficient and accurate initial boundary value problem (IBVP) solver, PFFT-QBEM, which allows for practical simulations of fully nonlinear three-dimensional wave-body interaction problems. Three nonlinear wave-body interaction problems, which are of scientific interest and practical importance, are investigated in detail: water surface impact of threedimensional objects, cavity dynamics in water entries, and coupled unstable motions of floating structures in waves. For the water impact problem, with the development of an adaptive jet flow treatment and an effective approach for accurately tracking water-body separation point/line, we obtain a thorough understanding of the gravity effect on the characteristics of slamming pressure/load on the object and free-surface profiles. For the cavity problem, we investigate the formation and evolution of an air cavity behind an object dropped into water (from air) at relatively low Froude numbers where the inertia and gravity effects are comparable. A theoretical solution is newly derived based on a matched asymptotic approach and a fully nonlinear numerical simulation is carried out, for the description of the kinematics and dynamics of the air cavity. Satisfactory quantitative comparisons are obtained among the theoretical predictions, numerical simulations, and existing experimental measurements for the dependence of cavity shape and closure time/height on Froude number and body geometry. For floating structures in waves, our focus is on the understanding of the fundamental mechanism and basic characteristics for coupled unstable heave-pitch motions of floating platforms/vessels. Through stability analyses, we identify that the second-order difference-frequency interaction between surface waves and body motions is the key mechanism for the excitation of unstable resonant motions. Fully nonlinear simulations are conducted to study the development of large-amplitude body motions and investigate quantitatively the dependence of the instability on related physical parameters, such as incident wave amplitude and phase, frequency detuning, body geometry, and system damping. Theoretical analyses and numerical simulations are verified by comparison to available experiments for the coupled unstable motions of a deep draft caisson vessel (DDCV).by Hongmei Yan.Ph.D.in Ocean Engineerin

Increasing prevalence of HIV and syphilis but decreasing rate of self-reported unprotected anal intercourse among men who had sex with men in Harbin, China: results of five consecutive surveys from 2006 to 2010

Background To monitor the prevalence of HIV and syphilis as well as behaviours, a sentinel site for men who have sex with men was established in Harbin in 2002. With additional funding, the sentinel surveillance evolved into annual cross-sectional surveys since 2006. Methods Behavioural and serological data collected in five consecutive cross-sectional surveys were analysed. SPSS 13.0 was applied to compare prevalence of HIV and syphilis as well as behavioural variables over time by demographic variables, bivariate and multivariate analysis. Results The prevalence of HIV and syphilis increased from 1.0% in 2006 to 7.5% in 2010 and from 9.2% in 2006 to 22.4% in 2009, respectively, whereas the rate of unprotected anal intercourse decreased from 61.3% in 2006 to 47.1% in 2010. Syphilis positivity and HIV infection are independently associated with each other across years. The rate of unprotected anal sex remains high although it has decreased over the years. Conclusion Findings support an increasing prevalence of HIV and syphilis among men who have sex with men in Harbin. Targeted behavioural intervention and syphilis treatment are urgently needed to prevent the epidemic from growin

Rethinking the Detection Head Configuration for Traffic Object Detection

Multi-scale detection plays an important role in object detection models. However, researchers usually feel blank on how to reasonably configure detection heads combining multi-scale features at different input resolutions. We find that there are different matching relationships between the object distribution and the detection head at different input resolutions. Based on the instructive findings, we propose a lightweight traffic object detection network based on matching between detection head and object distribution, termed as MHD-Net. It consists of three main parts. The first is the detection head and object distribution matching strategy, which guides the rational configuration of detection head, so as to leverage multi-scale features to effectively detect objects at vastly different scales. The second is the cross-scale detection head configuration guideline, which instructs to replace multiple detection heads with only two detection heads possessing of rich feature representations to achieve an excellent balance between detection accuracy, model parameters, FLOPs and detection speed. The third is the receptive field enlargement method, which combines the dilated convolution module with shallow features of backbone to further improve the detection accuracy at the cost of increasing model parameters very slightly. The proposed model achieves more competitive performance than other models on BDD100K dataset and our proposed ETFOD-v2 dataset. The code will be available.Comment: 26 pages, 4 figures, 7 table

Correlations of synergistic effect of glucocorticoids on tacrolimus with CYP3A, MDR1 and PXR gene polymorphisms in pediatric patients receiving liver transplantation for malignancy and chronic liver disease

Immune suppression after liver transplant for malignancy, such as hepatocellular carcinoma and end stage liver disease is done using immunosuppressant drugs like tacrolimus. As the immune system in children is not fully developed, combining immunosuppressants like glucocorticoids influence the efficacy and reduce the chances of transplant rejection, particularly in patients with gene polymorphism. However, whether interaction between glucocorticoid and tacrolimus is associated with CYP3A, MDR1, and PXR gene polymorphisms, remains unclear. Here, we explored correlations of synergistic effect of glucocorticoids on tacrolimus with CYP3A, MDR1 and PXR gene polymorphisms in pediatric patients receiving liver transplantation for malignancy and chronic liver disease. A total of 340 eligible children were divided into glucocorticoid (+) (n=148) and glucocorticoid () groups (n=192). They were given tacrolimus + mycophenolate mofetil, based on which glucocorticoid (+) group took prednisone acetate tablets for ≥12 months. The blood trough concentration of tacrolimus was detected by chemiluminescence microparticle immunoassay 1, 3, 6 and 12 months after medication, and blood drug concentration corrected by daily concentration/daily dose (C0/D) was calculated. CYP3A, MDR1 and PXR gene polymorphisms were analyzed using PCR-RFLP. GG, AG and AA genotypes of CYP3A were observed in 130, 166 and 44 cases, respectively. CC, CT and TT genotypes of MDR1 were found in 152, 142 and 46 cases, respectively. There were 252, 74 and 14 cases of WW, WM and MM genotypes of PXR, respectively. The distribution frequencies of GG and AG+AA genotypes had significant differences between the two groups. One month after medication, C0/D of tacrolimus of GG genotype in glucocorticoid (+) group significantly exceeded that of glucocorticoid () group. C0/D was significantly higher in glucocorticoid (+) group with AG+AA genotype1, 3, 6 and 12 months after medication (P <0.05)

Correlations of synergistic effect of glucocorticoids on tacrolimus with CYP3A, MDR1 and PXR gene polymorphisms in pediatric patients receiving liver transplantation for malignancy and chronic liver disease

705-710Immune suppression after liver transplant for malignancy, such as hepatocellular carcinoma and end stage liver disease is done using immunosuppressant drugs like tacrolimus. As the immune system in children is not fully developed, combining immunosuppressants like glucocorticoids influence the efficacy and reduce the chances of transplant rejection, particularly in patients with gene polymorphism. However, whether interaction between glucocorticoid and tacrolimus is associated with CYP3A, MDR1, and PXR gene polymorphisms, remains unclear. Here, we explored correlations of synergistic effect of glucocorticoids on tacrolimus with CYP3A, MDR1 and PXR gene polymorphisms in pediatric patients receiving liver transplantation for malignancy and chronic liver disease. A total of 340 eligible children were divided into glucocorticoid (+) (n=148) and glucocorticoid () groups (n=192). They were given tacrolimus + mycophenolate mofetil, based on which glucocorticoid (+) group took prednisone acetate tablets for ≥12 months. The blood trough concentration of tacrolimus was detected by chemiluminescence microparticle immunoassay 1, 3, 6 and 12 months after medication, and blood drug concentration corrected by daily concentration/daily dose (C0/D) was calculated. CYP3A, MDR1 and PXR gene polymorphisms were analyzed using PCR-RFLP. GG, AG and AA genotypes of CYP3A were observed in 130, 166 and 44 cases, respectively. CC, CT and TT genotypes of MDR1 were found in 152, 142 and 46 cases, respectively. There were 252, 74 and 14 cases of WW, WM and MM genotypes of PXR, respectively. The distribution frequencies of GG and AG+AA genotypes had significant differences between the two groups. One month after medication, C0/D of tacrolimus of GG genotype in glucocorticoid (+) group significantly exceeded that of glucocorticoid () group. C0/D was significantly higher in glucocorticoid (+) group with AG+AA genotype1, 3, 6 and 12 months after medication (P <0.05)