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61.
A. V. Radha Oscar Bomati-Miguel Sergey V. Ushakov Alexandra Navrotsky Pedro Tartaj 《Journal of the American Ceramic Society》2009,92(1):133-140
A fundamental issue that remains to be solved when approaching the nanoscale is how the size induces transformation among different polymorphic structures. Understanding the size-induced transformation among the different polymorphic structures is essential for widespread use of nanostructured materials in technological applications. Herein, we report water adsorption and high-temperature solution calorimetry experiments on a set of samples of single-phase monoclinic zirconia with different surface areas. Essential to the success of the study has been the use of a new ternary water-in-oil/water liquid solvothermal method that allows the preparation of monoclinic zirconia nanoparticles with a broad range of (BET) Brunauer–Emmett–Teller surface area values. Thus, the surface enthalpy for anhydrous monoclinic zirconia is reported for the first time, while that for the hydrous surface is a significant improvement over the previously reported value. Combining these data with previously published surface enthalpy for nanocrystalline tetragonal zirconia, we have calculated the stability crossovers between monoclinic and tetragonal phases to take place at a particle size of 28 ± 6 nm for hydrous zirconia and 34 ± 5 nm for anhydrous zirconia. Below these particle sizes, tetragonal hydrous and anhydrous phases of zirconia become thermodynamically stable. These results are within the margin of the theoretical estimation and confirm the importance of the presence of water vapor on the transformation of nanostructured materials. 相似文献
62.
A. V. Radha Grace S. Thomas P. Vishnu Kamath Churchil A. Antonyraj S. Kannan 《Bulletin of Materials Science》2010,33(3):319-324
The layered double hydroxide (LDH) of Co with Al decomposes to yield an oxide residue with the spinel structure below 250°C.
The decomposition reaction is preceded by the formation of an intermediate hydroxide in which the metal hydroxide layers are
regularly stacked about the c-crystallographic axis, but the layers themselves are aperiodic. Aperiodicity is modeled by locating randomly chosen Co2+ ions in tetrahedral sites in the interlayer region. This phase is characterized by a single strong basal reflection in its
powder diffraction pattern. All other reflections are extinguished on account of (i) turbostratic disorder which destroys
all hkl reflections and (ii) layer aperiodicity, which destroys all two dimensional hk reflections. Given its topochemical relationship with the spinel structure, such an intermediate is a necessary precursor
to spinel formation. 相似文献
63.
Processing of metallic materials using microwave energy has been a challenge. However, exploiting the size factor of particles in these candidate materials opened up further opportunities. The amount of heat evolved inside a particle per unit volume primarily depends upon its size, shape, electromagnetic and thermal properties. Finer particles can potentially absorb more microwave energy than coarser units and get heated rapidly with higher uniformity. It results in better properties in the processed part and energy economy. This work reviews the relevant literature and summarises fundamentals of microwave heating of metallic materials. Roles of particle size in processing these materials have been discussed. Challenges in microwave processing of finer metallic particles have been identified; opportunities for future research are outlined. 相似文献
64.
Radha Guha Author Vitae Nader Bagherzadeh Author Vitae Author Vitae 《Computers & Electrical Engineering》2009,35(2):258-285
There are many design challenges in the hardware-software co-design approach for performance improvement of data-intensive streaming applications with a general-purpose microprocessor and a hardware accelerator. These design challenges are mainly to prevent hardware area fragmentation to increase resource utilization, to reduce hardware reconfiguration cost and to partition and schedule the tasks between the microprocessor and the hardware accelerator efficiently for performance improvement and power savings of the applications.In this paper a modular and block based hardware configuration architecture named memory-aware run-time reconfigurable embedded system (MARTRES) is proposed for efficient resource management and performance improvement of streaming applications. Subsequently we design a task placement algorithm named hierarchical best fit ascending (HBFA) algorithm to prove that MARTRES configuration architecture is very efficient in increased resource utilization and flexible in task mapping and power savings. The time complexity of HBFA algorithm is reduced to O(n) compared to traditional Best Fit (BF) algorithm’s time complexity of O(n2), when the quality of the placement solution by HBFA is better than that of BF algorithm. Finally we design an efficient task partitioning and scheduling algorithm named balanced partitioned and placement-aware partitioning and scheduling algorithm (BPASA). In BPASA we exploit the temporal parallelism in streaming applications to reduce reconfiguration cost of the hardware, while keeping in mind the required throughput of the output data. We balance the exploitation of spatial parallelism and temporal parallelism in streaming applications by considering the reconfiguration cost vs. the data transfer cost. The scheduler refers to the HBFA placement algorithm to check whether contiguous area on FPGA is available before scheduling the task for HW or for SW. 相似文献
65.
66.
Kishan Radha; Zeelen Ph. Johan; Noble Martin E.M.; Borchert Torben V.; Mainfroid Veronique; Goraj Karine; Martial Joseph A.; Wierenga Rik K. 《Protein engineering, design & selection : PEDS》1994,7(8):945-951
Abstract The crystal structure of a hybrid Escherichia coli triosephosphateisomerase (TIM) has been determined at 2.8 Å resolution.The hybrid TIM (ETIM8CHI) was constructed by replacing the eighthß-unit of E.coli TIM with the equivalent unit of chickenTIM. This replacement involves 10 sequence changes. One of thechanges concerns the mutation of a buried alanine (Ala232 instrand 8) into a phenylalanine. The ETIM8CHI structure showsthat the A232F sequence change can be incorporated by a side-chainrotation of Phe224 (in helix 7). No cavities or strained dihedralsare observed in ETIM8CHI in the region near position 232, whichis in agreement with the observation that ETIM8CHI and E.coliTIM have similar stabilities. The largest CA (C-alpha atom)movements, 3 Å, are seen for the C-terminal end of helix8 (associated with the outward rotation of Phe224) and for theresidues in the loop after helix 1 (associated with sequencechanges in helix 8). From the structure it is not clear whythe kcat of ETIM8CHI is 10 times lower than in wild type E.coliTIM 相似文献
67.
Maximum-Likelihood Header Estimation: A Cross-Layer Methodology for Wireless Multimedia 总被引:1,自引:0,他引:1
We propose a novel cross-layer header estimation methodology that can be used by UDP-based wireless multimedia applications to estimate corrupted packet headers, thereby realizing significant throughput improvements. The proposed methodology requires only minor modifications to the protocol stack at the receiver while no modifications are needed to senders or intermediate nodes. We formulate header estimation as a problem of maximum-likelihood estimation of known parameters in noise. We derive likelihood functions for two wireless channel models, namely Markov and multifractal wavelet models. Our trace-driven video simulations at 2, 5.5 and 11 Mbps data rates of an 802.11b LAN demonstrate that significant improvements over normal UDP and UDP Lite can be achieved by employing header estimation with UDP. 相似文献
68.
We present new findings on the enthalpies of formation of vacancies and interstitial ion defects on either sublattice in the
alkali halide crystals MX (X=F, Cl, Br and M=Li, Na) using the MPPI model. The model uses a minimum fit to crystal properties
and is fully consistent with the dielectric response. The role of the non-Coulombic short range forcesvis-a-vis polarization fields in the stabilization of the defect formation process is examined and discussed in detail. It is shown
that it is important to treat the electrostatic polarization caused by the point defect carefully and variation in potential
modelling has a comparatively minor effect on the calculations of enthalpies of formation. 相似文献
69.
Silver halide crystals AgCl and AgBr exhibit all the three types of intrinsic point defects, namely, cationic Frenkel disorder,
Schottky disorder and the bound vacancy pair disorder. The ionic conductivity anomaly at high temperatures, the unusual behaviour
in respect of self- and impurity diffusion and the contrasting features in the anion self-diffusion between AgCl and AgBr
do not all satisfactorily fit into the prevailing models of ionic transport. We review these features critically. We also
discuss the potential and polarization models used in the theoretical evaluation of the enthalpies of formation of the intrinsic
defects in these crystals. Results of our recent investigations on these questions will be presented to highlight their implications
to the defect physics of these materials. 相似文献
70.
The recognition sequence of the Myb protein has been recently described to be pyAACKGHH (where py = T/C, K = G/T, and H = A/C/T), modifying the earlier identification as pyAACKG [Ording, E., et al. (1994) Eur. J. Biochem. 222, 113-120]. We had earlier determined the solution structure of the minimal cognate sequence TAACGG, choosing py = T and K = G, embeded in a 12-mer DNA duplex by NMR and related computational techniques [Radha, P. K., et al. (1995) Biochemistry 34, 5913-5912]. To understand the structural significance of the above modification and the role of the variability in the recognition sequence, we have investigated here the solution structure of a different DNA segment, d-ACAACTGCAGTTGT, which contains the extended Myb cognate site, CAACTGCA. The three-dimensional structure of the 14-mer duplex has been determined from NMR data by relaxation matrix and restrained molecular dynamics calculations. The structure of the above cognate sequence in the 14-mer duplex has been compared with that of the cognate sequence, TAACGG, in the 12-mer duplex and also with that in the NMR structure of the Myb DNA binding domain (R2R3)-DNA complex determined by Ogata et al. recently [Ogata, K., et al. (1994) Cell 79, 639-648]. The comparison highlighted differences in several structural parameters for the cognate sites in the DNA segments. Modeling studies by taking out the protein from the complex and presenting it with 12-mer and 14-mer DNA structures indicated that the protein induces structural alterations to drive the cognate site to a reasonably conserved structure. The extent of similarity of the derived structures was, however, dependent on the base sequences. Base changes in the minimal cognate sequence in the 12-mer-protein complex and in the 14-mer-protein complex so as to match the sequence of Ogata et al. produced a more conserved structure of the complex. A reverse exercise, in which the Ogata DNA in the complex was mutated to match the 12-mer and 14-mer minimal cognate sequences, complemented the above observations of the subtle sequence dependence of the structure in the complex. On the other hand, base changes in the extension did not influence the DNA-protein complex structure significantly. We also observed that the structural changes in the protein were very minor when different DNA sequences or different DNA structures were presented to it. These observations would be of interest from the point of view of DNA-Myb recognition. 相似文献