Electronic structure study of vanadium spinels by using density functional theory and dynamical mean field theory

Theoretically, various physical properties of AV$_{2}$O$_{4}$ (A=Zn, Cd and Mg) spinels have been extensively studied for last 15 years. Besides of this, no systematic comparative study has been done for these compounds, where the material specific parameters are used. Here, we report the comparative electronic behaviour of these spinels by using a combination of density functional theory and dynamical mean-field theory, where the self-consistent calculated Coulomb interaction $U$ and Hund's coupling $J$ (determined by Yukawa screening $\lambda$) are used. The main features, such as insulating band gaps ($E_{g}$), degree of itinerancy of V 3$d$ electrons and position of lower Hubbard band are observed for these parameters in these spinels. The calculated values of $E_{g}$ for ZnV$_{2}$O$_{4}$, CdV$_{2}$O$_{4}$ and MgV$_{2}$O$_{4}$ are found to be $\sim$0.9 eV, $\sim$0.95 eV and $\sim$1.15 eV, respectively, where the values of $E_{g}$ are close to experiment for ZnV$_{2}$O$_{4}$ and MgV$_{2}$O$_{4}$. The position of lower Hubbard band are observed around $\sim$-1.05 eV, $\sim$-1.25 eV and $\sim$-1.15 eV for ZnV$_{2}$O$_{4}$, CdV$_{2}$O$_{4}$ and MgV$_{2}$O$_{4}$, respectively, which are also in good agreement with the experimental data for ZnV$_{2}$O$_{4}$. The order of average impurity hybridization function of V site are found to be ZnV$_{2}$O$_{4}$$>$MgV$_{2}$O$_{4}$$>$CdV$_{2}$O$_{4}$. Hence, the degree of localization of V 3$d$ electrons is largest for CdV$_{2}$O$_{4}$ and smallest for ZnV$_{2}$O$_{4}$, which is in accordance with our earlier results. Hence, present work shows the importance of material specific parameters to understand the comparative electronic behaviour of these compounds.Comment: 7 pages, 5 figure

SLC: Memory Access Granularity Aware Selective Lossy Compression for GPUs

Memory compression is a promising approach for reducing memory bandwidth requirements and increasing performance, however, memory compression techniques often result in a low effective compression ratio due to large memory access granularity (MAG) exhibited by GPUs. Our analysis of the distribution of compressed blocks shows that a significant percentage of blocks are compressed to a size that is only a few bytes above a multiple of MAG, but a whole burst is fetched from memory. These few extra bytes significantly reduce the compression ratio and the performance gain that otherwise could result from a higher raw compression ratio. To increase the effective compression ratio, we propose a novel MAG aware Selective Lossy Compression (SLC) technique for GPUs. The key idea of SLC is that when lossless compression yields a compressed size with few bytes above a multiple of MAG, we approximate these extra bytes such that the compressed size is a multiple of MAG. This way, SLC mostly retains the quality of a lossless compression and occasionally trades small accuracy for higher performance. We show a speedup of up to 35% normalized to a state-of-the-art lossless compression technique with a low loss in accuracy. Furthermore, average energy consumption and energy-delay- product are reduced by 8.3% and 17.5%, respectively.EC/H2020/688759/EU/Low-Power Parallel Computing on GPUs 2/LPGPU

E²MC: Entropy Encoding Based Memory Compression for GPUs

Modern Graphics Processing Units (GPUs) provide much higher off-chip memory bandwidth than CPUs, but many GPU applications are still limited by memory bandwidth. Unfortunately, off-chip memory bandwidth is growing slower than the number of cores and has become a performance bottleneck. Thus, optimizations of effective memory bandwidth play a significant role for scaling the performance of GPUs. Memory compression is a promising approach for improving memory bandwidth which can translate into higher performance and energy efficiency. However, compression is not free and its challenges need to be addressed, otherwise the benefits of compression may be offset by its overhead. We propose an entropy encoding based memory compression (E2MC) technique for GPUs, which is based on the well-known Huffman encoding. We study the feasibility of entropy encoding for GPUs and show that it achieves higher compression ratios than state-of-the-art GPU compression techniques. Furthermore, we address the key challenges of probability estimation, choosing an appropriate symbol length for encoding, and decompression with low latency. The average compression ratio of E2MC is 53% higher than the state of the art. This translates into an average speedup of 20% compared to no compression and 8% higher compared to the state of the art. Energy consumption and energy-delayproduct are reduced by 13% and 27%, respectively. Moreover, the compression ratio achieved by E2MC is close to the optimal compression ratio given by Shannon's source coding theorem.EC/H2020/688759/EU/Low-Power Parallel Computing on GPUs 2/LPGPU

Degradation Kinetics and Mechanical Studies of Intumescent Coated Cotton Fabric

In the present study, cotton fabric were prepared via coating with intumescent formulations of ammonium polyphosphate (APP), guanidine nitrate, penta erythritol (PER) and metal salts at different loading levels via 'Pad-dry cure' method. Thermal degradation behavior of prepared cotton derivatives was investigated by thermogravimetry (TG) and differential thermal analysis (DTA) from ambient temperature to 700 oC. Dynamic TG analysis was used to study the thermal degradation behavior of samples at four different heating rates of 2, 5, 10 and 20 oC min-1 in air atmosphere. The treated cotton fabric decomposes at lower temperatures and produces higher amount of char yields. The degradation activation energy was calculated using Friedman, modified Coats-Redfern and Ozawa-Flynn-Wall (O-F-W) iso-conversional model free methods. Tensile properties of coated fabric were found to be reduced with increase in loading of intumescent formulation but there was an abrupt increase in sample coated with intumescent and silica. With the insertion of iron (Fe) metal ion along with intumescent reduces the fabric strength due to formation of metal complexes with cotton cellulose which decreases the crosslinking. The maximum flame ratardancy of CF 12APP-Si among all cotton derivatives is suggested as the flame retardancy directly proportional to char yield (22 % at 650 oC) that is highest and inversely proportional to MMLR value (8.3 % min-1), that is least among all samples. Based on thermal and kinetic studies, the optimum concentration of flame retardant is worked out