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排序方式: 共有866条查询结果,搜索用时 375 毫秒
81.
Wei-lun Hung Yuan Xie Narayanan Vijaykrishnan Mahmut Kandemir Mary Jane Irwin 《Journal of Signal Processing Systems》2010,58(2):145-160
Power consumption is a top priority in high performance circuit design today. Many low power techniques have been proposed
to tackle the ever serious, highly pressing power consumption problem, which is composed of both dynamic and static power
in the nanometer era. The static power consumption nowadays receives even more attention than that of dynamic power consumption
when technology scales below 100 nm. In order to mitigate the aggressive power consumption, various existing low power techniques
are often used; however, they are often applied independently or combined with two or at most three different techniques together,
and that is not sufficient to address the escalating power issue. In this paper, we present a power optimization framework
for the minimization of total power consumption in combinational logic through multiple V
dd
assignment, multiple V
th
assignment, device sizing, and stack forcing, while maintaining performance requirements. These four power reduction techniques
are properly encoded into the genetic algorithm and evaluated simultaneously. The overhead imposed by the insertion of level
converters is also taken into account. The effectiveness of each power reduction mechanism is verified, as are the combinations
of different approaches. Experimental results are presented for a number of 65 nm benchmark circuits that span typical circuit
topologies, including inverter chains, SRAM decoders, multiplier, and a 32 bit carry adder. Our experiments show that the
combination of four low power techniques is the effective way to achieve low power budget. The framework is general and can
be easily extended to include other design-time low power techniques, such as multiple gate length or multiple gate oxide
thickness. 相似文献
82.
Jaehak Jeong Narayanan Kannan Jeff Arnold Roger Glick Leila Gosselink Raghavan Srinivasan 《Water Resources Management》2010,24(15):4505-4527
Increasing urbanization changes runoff patterns to be flashy and instantaneous with decreased base flow. A model with the
ability to simulate sub-daily rainfall–runoff processes and continuous simulation capability is required to realistically
capture the long-term flow and water quality trends in watersheds that are experiencing urbanization. Soil and Water Assessment
Tool (SWAT) has been widely used in hydrologic and nonpoint sources modeling. However, its subdaily modeling capability is
limited to hourly flow simulation. This paper presents the development and testing of a sub-hourly rainfall–runoff model in
SWAT. SWAT algorithms for infiltration, surface runoff, flow routing, impoundments, and lagging of surface runoff have been
modified to allow flow simulations with a sub-hourly time interval as small as one minute. Evapotranspiration, soil water
contents, base flow, and lateral flow are estimated on a daily basis and distributed equally for each time step. The sub-hourly
routines were tested on a 1.9 km2 watershed (70% undeveloped) near Lost Creek in Austin Texas USA. Sensitivity analysis shows that channel flow parameters
are more sensitive in sub-hourly simulations (Δt = 15 min) while base flow parameters are more important in daily simulations (Δt = 1 day). A case study shows that the sub-hourly SWAT model reasonably reproduces stream flow hydrograph under multiple storm
events. Calibrated stream flow for 1 year period with 15 min simulation (R
2 = 0.93) shows better performance compared to daily simulation for the same period (R
2 = 0.72). A statistical analysis shows that the improvement in the model performance with sub-hourly time interval is mostly
due to the improvement in predicting high flows. The sub-hourly version of SWAT is a promising tool for hydrology and non-point
source pollution assessment studies, although more development on water quality modeling is still needed. 相似文献
83.
The heat transfer effectiveness of nanofluids is adversely affected by the delay in convection onset. The lesser effectiveness, when compared to that of base fluid, is observed in a range of nanofluid layer thickness. The heat transfer coefficient of water–Al2O3 nanofluid can be enhanced by sustaining the equilibrium between Rayleigh number, temperature, particle volume fraction, and enclosure aspect ratio. In this paper, the specific correlation of fluid layer thickness and the onset of convection, which can significantly dominate the heat transfer characteristics of nanofluids are investigated using the concept of critical Rayleigh number. The water layer thickness for convection onset is first experimentally assessed for different real-life heat flux densities. It is then performed for Al2O3–water nanofluid for varying volume fractions. With the increase in volume fraction even though thermal conductivity increases, the overall heat transfer enhancement of the nanofluid is reduced. Temperature involved (heat flux density), the volume fraction of the nanofluid used, nanofluid layer thickness (space availability for the cooling system), and mass of the nanoparticle influence heat transfer enhancement. A higher volume fraction may not always result in enhancement of heat transfer as far as nanofluids are concerned. 相似文献
84.
Effect of Thermal Oxidation on Corrosion Resistance of Commercially Pure Titanium in Acid Medium 总被引:1,自引:0,他引:1
M. Jamesh Satendra Kumar T. S. N. Sankara Narayanan 《Journal of Materials Engineering and Performance》2012,21(6):900-906
This article addresses the characteristics of commercially pure titanium (CP-Ti) subjected to thermal oxidation in air at 650?°C for 48?h and its corrosion behavior in 0.1 and 4?M HCl and HNO3 mediums. Thermal oxidation of CP-Ti leads to the formation of thick oxide scales (~20???m) throughout its surface without any spallation. The oxide layer consists of rutile- and oxygen-diffused titanium as predominant phases with a hardness of 679?±?43?HV1.96. Electrochemical studies reveal that the thermally oxidized CP-Ti offers a better corrosion resistance than its untreated counterpart in both HCl and HNO3 mediums. The uniform surface coverage and compactness of the oxide layer provide an effective barrier toward corrosion of CP-Ti. The study concludes that thermal oxidation is an effective approach to engineer the surface of CP-Ti so as to increase its corrosion resistance in HCl and HNO3 mediums. 相似文献
85.
The characteristics of Ti6Al4V alloy subjected to thermal oxidation in air atmosphere at 650 °C for 48 h and its corrosion behavior in 0.1 and 4 M HCl and HNO3 medium are addressed. When compared to the naturally formed oxide layer (~4–6 nm), a relatively thicker oxide scale (~7 µm) is formed throughout the surface of Ti6Al4V alloy after thermal oxidation. XRD pattern disclose the formation of the rutile and oxygen‐diffused titanium as the predominant phases. A significant improvement in the hardness (from 324 ± 8 to 985 ± 40 HV0.25) is observed due to the formation of hard oxide layer on the surface followed by the presence of an oxygen diffusion zone beneath it. Electrochemical studies reveal that the thermally oxidized Ti6Al4V alloy offers a better corrosion resistance than its untreated counterpart in both HCl and HNO3 medium. The uniform surface coverage, compactness and thickness of the oxide layer provide an effective barrier towards corrosion of the Ti6Al4V alloy. The study concludes that thermal oxidation is an effective approach to engineer the surface of Ti6Al4V alloy to increase its corrosion resistance in HCl and HNO3 medium. 相似文献
86.
The enhanced mobile membranes is a variant of membrane systems which has been proposed for describing some biological mechanisms
of the immune system. In this paper, we study the computational power of the enhanced mobile membranes. In particular, we
focus on the power of mobility given by the operations endo, exo, fendo and fexo. The computational universality is obtained with 12 membranes, while systems with 8 membranes subsume PsET0L, and those with 3 membranes are contained in PsMAT. 相似文献
87.
Hybrid magnetic nanostructures with high coercivity have immense application potential in various fields. Nickel (Ni) electrodeposited inside Cobalt (Co) nanotubes (a new system named Ni @ Co nanorods) were fabricated using a two-step potentiostatic electrodeposition method. Ni @ Co nanorods were crystalline, and they have an average diameter of 150 nm and length of ~15 μm. The X-ray diffraction studies revealed the existence of two separate phases corresponding to Ni and Co. Ni @ Co nanorods exhibited a very high longitudinal coercivity. The general mobility-assisted growth mechanism proposed for the growth of one-dimensional nanostructures inside nano porous alumina during potentiostatic electrodeposition is found to be valid in this case too. 相似文献
88.
This paper presents selective checkpointing and rollback schemes for MT-OO (multithreaded, object-oriented) programs. There is a need for checkpointing mechanisms that are more sophisticated than the traditional process-level checkpointing. The program model, theoretical foundations, and an implementation of the selective checkpointing and rollback schemes are described. The usefulness of the schemes is demonstrated by implementing a higher level fault-tolerance scheme of conversations using them. The performance implications are studied on a prototype Internet e-commerce-server. The use of the selective schemes in the prototype server showed an appreciable reduction in the loss of work in the presence of faults. Benefits are more pronounced for a larger level of concurrency in the server. The selective scheme usually outperforms the hypothetical zero-cost global scheme in the presence of faults, vis-a-vis completion times. The experiments also show the vast difference between the sizes of selective checkpoints and global checkpoints. The concurrent sessions scheme (based on the concept of relaxed conversations) required 160 checkpoints in less than an hour. Traditionally, such a scheme would be considered outrageous, but the selective schemes still improve performance in the presence of faults 相似文献
89.
Chidambaram Narayanan Reto BalzDaniel A. Weiss Kurt C. Heiniger 《Journal of Materials Processing Technology》2013,213(12):2201-2210
A phenomenological model of the three-phase flow inside an abrasive water jet machining cutting head has been developed. Several improvements over previously presented models such as taking into account the abrasive particle size distribution, and the effect of breakage of particles on the energy flux have been made. The model has been validated using an extensive set of experimental data with wide variations in cutting-head geometry, operating pressure, and abrasive mass flow rates. The cross-sectional averaged abrasive particle velocity at the exit of the focussing tube has been predicted with good accuracy over the whole range of experiments. In particular, the Pearson correlation between the model and the experimental results is found to be more than 95%, implying the utility of this model in design. 相似文献
90.
T. Balusamy Satendra Kumar T. S. N. Sankara Narayanan 《Transactions of the Indian Institute of Metals》2011,64(4-5):507-511
Stainless steels are widely used as orthopedic implant materials. The main problems with these implant materials are fatigue fracture, fretting fatigue, wear and corrosion. Surface mechanical attrition treatment (SMAT) is a newly developed method to improve the materials properties and performance. In the present study, AISI 304 SS was subjected to SMAT using 2, 5 and 8 mm ? 316L SS balls for 15, 30, 45 and 60 min at 50 Hz under vacuum. SMAT of 304 SS increased the surface roughness, induced the formation of mechanical twins, strain induced martensite phase, and increased the defect density, which is a function of the size of the balls and treatment time. SMAT using 5 and 8 mm ? balls significantly decreased the corrosion resistance whereas treatment using 2 mm ? balls enabled an anodic shift in Ecorr and a marginal decrease in icorr. However, increase in surface roughness leads to the formation of a defective passive film and a decrease in breakdown potential. 相似文献