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排序方式: 共有212条查询结果,搜索用时 15 毫秒
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In the present research work, a non-edible oil source Cucumis melo var. agrestis(wild melon) was systematically identified and studied for biodiesel production and its characterization. The extracted oil was 29.1% of total dry seed weight. The free fatty acid value of the oil was found to be 0.64%, and the single-step alkaline transesterification method was used for conversion of fatty acids into their respective methyl esters. The maximum conversion efficiency of fatty acids was obtained at 0.4 wt% Na OH(used as catalyst), 30%(methanol to oil, v/v) methanol amount, 60 ℃ reaction temperature,600-rpm agitation rate and 60-min reaction time. Under these optimal conditions, the conversion efficiency of fatty acid was 92%. However, in the case of KOH as catalyst, the highest conversion(85%) of fatty acids was obtained at 40%methanol to oil ratio, 1.28 wt% KOH, 60 ℃ reaction temperature, 600-rpm agitation rate and 45 min of reaction time.Qualitatively, biodiesel was characterized through Fourier transform infrared spectroscopy(FTIR) and gas chromatography and mass spectroscopy(GC–MS). FTIR results demonstrated a strong peak at 1742 cm~(-1), showing carbonyl groups(C=O)of methyl esters. However, GC–MS results showed the presence of twelve methyl esters comprised of lauric acid, myristic acid, palmitic acid, non-decanoic acid, hexadecanoic acid, octadecadienoic acid and octadecynoic acid. The fuel properties were found to fall within the range recommended by the international biodiesel standard, i.e., American Society of Testing Materials(ASTM): flash point of 91 ℃, density of 0.873 kg/L, viscosity of 5.35 c St, pour point of-13 ℃, cloud point of-10 ℃, total acid number of 0.242 mg KOH/g and sulfur content of 0.0043 wt%. The present work concluded the potential of wild melon seed oil as excellent non-edible source of bioenergy. 相似文献
3.
The onset of Darcy‐Brinkman convection in a binary viscoelastic fluid‐saturated sparsely packed porous layer with an internal heat source is studied using both linear and nonlinear stability analyses. The Oldroyd‐B model is employed to describe the rheological behavior of binary fluid. An extended form of the Darcy‐Oldroyd law incorporating Brinkman's correction and time derivative is used to describe the flow through a porous layer. The onset criterion for stationary, oscillatory, and finite amplitude convection is derived analytically. There is a competition between the processes of thermal diffusion, solute diffusion, and viscoelasticity that causes the convection to set in through an oscillatory mode rather than a stationary mode. The effect of internal Rayleigh number, relaxation and retardation parameters, solute Rayleigh number, Darcy number, Darcy‐Prandtl number, and Lewis number on the stability of a system is investigated and is shown graphically. The nonlinear theory based on the truncated representation of the Fourier series method is used to find heat and mass transfer. The transient behavior of the Nusselt and Sherwood numbers is obtained using numerical methods. Some known results are recovered for the particular cases of the present study. © 2013 Wiley Periodicals, Inc. Heat Trans Asian Res, 42(8): 676–703, 2013; Published online in Wiley Online Library ( wileyonlinelibrary.com/journal/htj ). DOI 10.1002/htj.21056 相似文献
4.
SJ Victor DM Brown EM Horwitz AA Martinez VR Kini JE Pettinga KW Shaheen P Benitez PY Chen FA Vicini 《Canadian Metallurgical Quarterly》1998,82(7):1303-1309
BACKGROUND: Analyses were performed to determine local control and cosmetic outcome of breast carcinoma patients with prosthetically augmented or reconstructed breasts who had received radiation therapy (RT). METHODS: Twenty-one newly diagnosed breast carcinoma patients with prosthetically augmented or reconstructed breasts were treated with external beam RT. All patients received whole breast RT (median dose, 50.4 gray [Gy]) and 19 were boosted to a median dose of 60.4 Gy. A median dose of 50.4 Gy was delivered to the regional lymph nodes in 12 patients. Tissue equivalent bolus material was used in six patients. Seventeen patients received adjuvant systemic therapy. Cosmetic results were evaluated at 3-6-month intervals. RESULTS: With a median follow-up of 32 months, good/excellent cosmetic results were observed in 71% of patients (100% in those with augmented breasts and 54% in those with reconstructed breasts). Four patients (19%) with fair/poor cosmetic outcomes required implant removal and/or revision. Multiple clinical and treatment-related factors were analyzed for their impact on cosmetic outcome. A worsened cosmetic result was observed with increasing stage (P = 0.076), breast reconstruction (vs. augmentation) (P = 0.030), and bolus application (P = 0.016). All patients with fair/poor cosmetic outcomes had time intervals from implant insertion to RT ranging from 53-213 days. Two patients developed an isolated local recurrence within the augmented breast. CONCLUSIONS: Patients with prosthetically augmented breasts can undergo RT and expect good/excellent cosmetic results. Patients with reconstructed breasts are at a significantly greater risk for cosmetic failure. This risk may be related to the higher percentage of patients with advanced disease, those who received bolus application, and those who received earlier delivery of RT (after the cosmetic procedure) in reconstructed breasts. 相似文献
5.
Overhead factors for data networks using message-switching or packet-switching techniques are defined and analysed. The transmission lines are assumed to have only random errors and the acknowledgments are handled on a `stop-and-wait? strategy. For packet switching, the packet size used is such that, in each case, the overhead factor is minimised. Results show that the overheads for packet switching tend to be much higher than for message switching when the line error rates are low, i.e. better than 10?5. It is concluded that, although packet switching has several significant merits, these are achieved at the expense of a substantial increase in overheads. 相似文献
6.
D. C. Olson S. E. Shaheen M. S. White W. J. Mitchell M. F. A. M. van Hest R. T. Collins D. S. Ginley 《Advanced functional materials》2007,17(2):264-269
The power conversion efficiency of organic and hybrid solar cells is commonly reduced by a low open‐circuit voltage (VOC). In these cases, the VOC is significantly less than the energy of the lowest energy absorbed photon, divided by the elementary charge q. The low photovoltage originates from characteristically large band offsets between the electron donor and acceptor species. Here a simple method is reported to systematically tune the band offset in a π‐conjugated polymer–metal oxide hybrid donor–acceptor system in order to maximize the VOC. It is demonstrated that substitution of magnesium into a zinc oxide acceptor (ZnMgO) reduces the band offset and results in a substantial increase in the VOC of poly(3‐hexylthiophene) (P3HT)–ZnMgO planar devices. The VOC is seen to increase from 500 mV at x = 0 up to values in excess of 900 mV for x = 0.35. A concomitant increase in overall device efficiency is seen as x is increased from 0 to 0.25, with a maximum power‐conversion efficiency of 0.5 % obtained at x = 0.25, beyond which the efficiency decreases because of increased series resistance in the device. This work provides a new tool for understanding the role of the donor–acceptor band offset in hybrid photovoltaics and for maximizing the photovoltage and power‐conversion efficiency in such devices. 相似文献
7.
8.
Ahmed A. Shaheen Aminah Robinson Fayek S. M. AbouRizk 《Canadian Metallurgical Quarterly》2007,133(4):325-334
Range estimating is a simple form of simulating a project estimate by breaking the project into work packages and approximating the variables in each package using statistical distributions. This paper explores an alternate approach to range estimating that is grounded in fuzzy set theory. The approach addresses two shortcomings of Monte Carlo simulation. The first is related to the analytical difficulty associated with fitting statistical distributions to subjective data, and the second relates to the required number of simulation runs to establish a meaningful estimate of a given parameter at the end of the simulation. For applications in cost estimating, the paper demonstrates that comparable results to Monte Carlo simulation can be achieved using the fuzzy set theory approach. It presents a methodology for extracting fuzzy numbers from experts and processing the information in fuzzy range estimating analysis. It is of relevance to industry and practitioners as it provides an approach to range estimating that more closely resembles the way in which experts express themselves, making it practically easy to apply an approach. 相似文献
9.
Levine MD Shaheen SI 《IEEE transactions on pattern analysis and machine intelligence》1981,(5):540-556
The objective of a computer vision system is to outline the objects in a picture and label them with an appropriate interpretation. This paper proposes a new paradigm for a modular computer vision system which is both data directed and knowledge based. The system consists of three different types of units, two of which are associative data memories implemented as relational databases. The short-term memory (STM) contains the raw color picture data and the most current interpretations and deductions about the original scene. The long-term memory (LTM) contains a detailed model of the scene under consideration. A collection of analysis processors, each of which is specialized for a particular task, can communicate with both of these memories. The information in the LTM remains unchanged during the analysis, while the STM is being continually updated and revised by the appropriate processors. The latter may be conceived of as being activated by certain data conditions in the STM, and using the information in both the LTM and STM to alter the status of the STM. 相似文献
10.
Shaheen Sultana Sushama Talegaonkar Raisuddin Ali Gaurav Mittal Aseem Bhatnagar Farhan J. Ahmad 《Powder Technology》2011,211(1):1-9
The purpose of this research work was to formulate and evaluate alpha ketoglutarate nanoparticles as dry powder inhaler for treatment of cyanide poisoning. Non-polymeric particles were prepared by nano-precipitation technique using various stabilizers. Selection of co-solvent and stabilizer was a key to produce stabilized particles. A combination of lutrol F68 and PVA as a crystal growth inhibitor seems to be best in achieving minimum particle size of 110.2 nm. On the basis of preliminary trials a Box-Behnken statistical design was employed to study the effect of independent variables, drug concentration (X1), stirring speed (X2), stirring time (X3), PVA concentration (X4), poloxomer concentration (X5) and volume of co-solvent (X6) on average particle size. Particle size varied from 110 to 875 nm depending upon the significant terms. Optimized formulation was predicted at drug concentration (50 μg/ml), stirring speed (640 rpm), stirring time (1 min), PVA concentration (1%), poloxomer concentration (1.69%) and volume of co-solvent (30 ml) with 104.6% experimental validity. The nanosized particles were further characterized by X-ray diffraction (XRD), Differential Scanning Calorimetry (DSC), Nuclear Magnetic Resonance (NMR) and Fourier Transform Infrared Spectroscopy (FT-IR) analysis. The results of particle characterization indicate that there was no physical disparity when compared with the commercial α-KG sample. 相似文献