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排序方式: 共有87条查询结果,搜索用时 15 毫秒
1.
Franjo Ivančić Zijiang Yang Malay K. Ganai Aarti Gupta Pranav Ashar 《Theoretical computer science》2008
This paper discusses our methodology for formal analysis and automatic verification of software programs. It is applicable to a large subset of the C programming language that includes pointer arithmetic and bounded recursion. We consider reachability properties, in particular whether certain assertions or basic blocks are reachable in the source code, or whether certain standard property violations can occur. We perform this analysis via a translation to a Boolean circuit representation based on modeling basic blocks. The program is then analyzed by a back-end SAT-based bounded model checker, where each unrolling is mapped to one step in a block-wise execution of the program. 相似文献
2.
Force-distance curve measurements using atomic force microscope (AFM) has been widely used in a broad range of areas. However, currently force-curve measurements are hampered the its low speed of AFM. In this article, a novel inversion-based iterative control technique is proposed to dramatically increase the speed of force-curve measurements. Experimental results are presented to show that by using the proposed control technique, the speed of force-curve measurements can be increased by over 80 times--with no loss of spatial resolution--on a commercial AFM platform and with a standard cantilever. High-speed force curve measurements using this control technique are utilized to quantitatively study the time-dependent elastic modulus of poly(dimethylsiloxane) (PDMS). The force-curves employ a broad spectrum of push-in (load) rates, spanning two-order differences. The elastic modulus measured at low-speed compares well with the value obtained from dynamic mechanical analysis (DMA) test, and the value of the elastic modulus increases as the push-in rate increases, signifying that a faster external deformation rate transitions the viscoelastic response of PDMS from that of a rubbery material toward a glassy one. 相似文献
3.
4.
Ruqin Zhang Xiaoping Wang Pranav Shrotriya Rana Biswas Ashraf Bastawros 《Machining Science and Technology》2013,17(4):515-530
Mechanistic numerical analysis and molecular dynamics (MD) simulation are employed to understand the material detachment mechanism associated with chemical mechanical polishing. We investigate the mechanics of scratch intersection mechanism to obtain a characteristic length scale and compare the theoretical predictions with previous experimental observations on ductile copper discs at the micro-scale. First, an analytical model is developed based on mechanics of materials approach. The analytical model includes the effects of strain hardening during material removal as well as the geometry of indenter tip. In the next step, molecular simulations of the scratch intersection are performed at the atomistic scale. The embedded atom method (EAM) is utilized as the force field for workpiece material and a simplified tool-workpiece interaction is assumed to simulate material removal through scratch intersection mechanism. Both models are utilized to predict a characteristic length of material detachment related to material removal during scratch intersection. The predictions from two approaches are compared with experimental observations in order to draw correlations between experiment and simulation. The insights obtained from this work may assist in understanding the mechanism for chemical mechanical planarization (CMP), and even be applied to other different machining and polishing events. 相似文献
5.
Production of aromatics by catalytic fast pyrolysis of cellulose in a bubbling fluidized bed reactor
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Pranav U. Karanjkar Robert J. Coolman George W. Huber Michael T. Blatnik Saba Almalkie Stephen M. de Bruyn Kops Triantafillos J. Mountziaris William C. Conner 《American Institute of Chemical Engineers》2014,60(4):1320-1335
Catalytic fast pyrolysis of cellulose was studied at 500°C using a ZSM‐5 catalyst in a bubbling fluidized bed reactor constructed from a 4.92‐cm ID pipe. Inert gas was fed from below through the distributor plate and from above through a vertical feed tube along with cellulose. Flowing 34% of the total fluidization gas through the feed tube led to the optimal mixing of the pyrolysis vapors into the catalyst bed, which experimentally corresponded to 29.5% carbon aromatic yield. Aromatic yield reached a maximum of 31.6% carbon with increasing gas residence time by changing the catalyst bed height. Increasing the hole‐spacing in the distributor plate was shown to have negligible effect on average bubble diameter and hence did not change the product distribution. Aromatic yields of up to 39.5% carbon were obtained when all studied parameters were optimized. © 2014 American Institute of Chemical Engineers AIChE J, 60: 1320–1335, 2014 相似文献
6.
Wande Zhang Pranav Soman Kyle Meggs Xin Qu Shaochen Chen 《Advanced functional materials》2013,23(25):3226-3232
Cells sense and respond to mechanical forces, regardless of whether the source is from a normal tissue matrix, an adjacent cell or a synthetic substrate. In recent years, cell response to surface rigidity has been extensively studied by modulating the elastic modulus of poly(ethylene glycol) (PEG)‐based hydrogels. In the context of biomaterials, Poisson's ratio, another fundamental material property parameter has not been explored, primarily because of challenges involved in tuning the Poisson's ratio in biological scaffolds. Two‐photon polymerization is used to fabricate suspended web structures that exhibit positive and negative Poisson's ratio (NPR), based on analytical models. NPR webs demonstrate biaxial expansion/compression behavior, as one or multiple cells apply local forces and move the structures. Unusual cell division on NPR structures is also demonstrated. This methodology can be used to tune the Poisson's ratio of several photocurable biomaterials and could have potential implications in the field of mechanobiology. 相似文献
7.
Amit Saxena Abha Sharma Avanish Kumar Srivastava Beer Singh Pranav Kumar Gutch Rajendra Prasad Semwal 《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》2009,84(12):1860-1872
BACKGROUND: Chemical warfare (CW) agents are highly toxic compounds and have been used in war to produce physical immobilization, so safe and effective ways to detoxify them without endangering human life or the environment is of great concern. One of the important ways to achieve protection against CW agents contaminating air is to utilize suitable adsorbent materials, e.g. activated carbon, nanoparticles, etc. In the present study nanoparticles, synthesized through sol–gel processes and loaded with reactive compounds have been used for the degradation of CW agents and to understand their adsorption kinetics using Fickian and linear driving force models. RESULTS: Nanoparticles of AP‐Al2O3 (aerogel‐produced alumina) in the size range 2–30 nm with high surface area (375 m2 g?1) were produced by an alkoxide‐based synthesis, and then characterized using N2‐Brunauer–Emmet–Teller (BET), scanning electron microscopy (SEM), transmission electron microscopy (TEM), X‐ray diffraction (XRD) and thermogravimetric analysis (TGA) techniques. Thereafter, these were impregnated, and finally tested for kinetics of adsorption of sulfur mustard (HD) under static conditions. The kinetics was studied using linear driving force and Fickian diffusion models and the kinetics parameters determined. CONCLUSION: AP‐Al2O3 with 10% impregnation of 9‐molybdo‐3‐vanadophosphoric acid (10%, w/w) showed the maximum uptake (640 mg g?1) of HD. The highest adsorption potential indicated that the adsorption was due not only to physisorption but also involved chemisorption. Values of the diffusional exponent indicated the mechanism to be Fickian and anomalous. Hydrolysis, dehydrochlorination and oxidation reactions (identified using gas chromatography‐mass spectrometry (GC/MS)) were found to be the route of degradation of HD over the prepared nanoparticle based adsorbents. Copyright © 2009 Society of Chemical Industry 相似文献
8.
Yixian Wang Pal Molian Pranav Shrotriya 《The International Journal of Advanced Manufacturing Technology》2014,70(5-8):1009-1022
An improved method for cutting thick polycrystalline cubic boron nitride (PCBN) tool blanks is explored because current methods of pulsed Nd:YAG laser cutting and wire electrical discharge machining (EDM) are constrained by low speed and low precision. We present a CO2 laser/waterjet (LWJ) process to cut 4.8-mm-thick PCBN tool inserts by a crack separation mechanism. In LWJ, the PCBN blank is locally heated using a high-power continuous wave CO2 laser to cause phase transition from cubic to hexagonal followed by water quenching to generate thermal stresses and form boron oxide leading to increased brittleness, subsequent cracking, and material separation. A 23 fractional design of experiment (DOE) approach was employed to determine the factors of laser power, cutting speed, and waterjet pressure on the responses of phase transformation depth, taper, and surface roughness. A numerical heat flow model, based on Green’s function, was used to calculate the temperature distributions along the depth. Surface profilometer, scanning electron microscopy, and Raman spectroscopy were utilized to analyze the phase transformation and crack zones. Results from LWJ compared with pulsed Nd:YAG laser and laser microjet? methods indicate LWJ cuts 30 times faster; this was attributed to a nonconventional material removal (crack separation) mechanism. When LWJ was compared against nitrogen-assisted CO2 laser cutting, improved cut quality (less taper and smaller heat-affected zone) was observed due to a greater control on phase transformation and crack propagation. DOE analysis revealed laser power and waterjet pressure, and the interactions among them are more significant factors than others. 相似文献
9.
Pranav M. Pawar Rasmus H. Nielsen Neeli R. Prasad Ramjee Prasad 《Wireless Personal Communications》2014,74(4):1213-1229
Wireless sensor networks (WSNs) enable a wide variety of applications resulting in still increasing requirements for the protocols supporting the operations. The medium access control (MAC) layer protocols are essential for improving the performance of an application and its quality of service because MAC protocols influence channel capacity utilization, network delay, energy consumption, and scalability. The contribution of this paper is two novel cluster-based time division multiple access (TDMA) scheduling MACs for WSNs and an analysis of the mobility impact on both. The proposed MAC layer protocols support real time applications where the cluster-based scheduling improves the scalability and also improves the performance in varying network conditions. The paper presents the design, implementation and performance evaluation of the proposed cluster based TDMA scheduling algorithms green conflict free (GCF) and multicolor-GCF (M-GCF) for high complexity and high requirement applications of WSNs under both low and high mobility conditions. The comparative evaluation shows that the M-GCF algorithm has better slot sharing and less conflicts with reduced communication energy consumption, delay, and good throughput under static and low mobility conditions while the GCF algorithm has better performance in high mobility scenarios. The paper also defines the mobility threshold that decides the use of the GCF- and M-GCF algorithms according to the mobility requirement of application. 相似文献
10.