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排序方式: 共有560条查询结果,搜索用时 234 毫秒
101.
Carlos M. García Santander Sandra M. Gómez Rueda Nívea de Lima da Silva Celso L. de Camargo Theo G. Kieckbusch M. Regina Wolf Maciel 《Fuel》2012,92(1):158-161
At present, a large number of studies of biodiesel production process using simulation packages are being developed. In these studies, vegetable oils and biodiesels are characterized in the software through representative compounds because of they are not in the compounds database of commercial simulators. With the aim to achieve a successfully characterization in these kinds of software, some properties of the substances must be available. The normal boiling point (NBP) is the most important property due to the fact that this property along with group contribution methods allows other properties calculation such as, e.g., critical properties and temperature dependency properties. In this work, a thermogravimetric analysis (TGA) method for rapid measurement of normal boiling points of two triacylglycerols and four ethyl esters, i.e., triolein, tripalmitin, ethyl oleate, ethyl palmitate, ethyl linoleate and ethyl ricinoleate, was used. Nowadays, in the open literature exists few data available about ethyl esters properties; hence, the results obtained here will contribute in the proposal, analysis, and evaluation of ethyl esters (biodiesel) virtual plants using reliable simulation packages. In addition, a more accurate characterization of compounds and therefore more accurate simulation results can be obtained when they are used. 相似文献
102.
Mathias Schröder Alexander Haußmann Andreas Thiessen Elisabeth Soergel Theo Woike Lukas M. Eng 《Advanced functional materials》2012,22(18):3936-3944
Ferroic materials play an increasingly important role in novel (nano)electronic devices. Recently, research on domain walls (DWs) receives a big boost by the discovery of DW conductivity (DWC) in BiFeO3 and Pb(ZrxTi1‐x)O3 ferroic thin films. Here, it is demonstrated that DWC is not restricted to thin films, but equally applies to millimeter‐thick wide‐bandgap, ferroic single crystals, such as LiNbO3. In this material transport along DWs can be switched by super‐bandgap illumination and tuned by engineering the tilting angle of DWs with respect to the polar axis. The results are consistently obtained using conductive atomic force microscopy to locally map the DWC and macroscopic contacts, thereby in addition investigating the temperature dependence, DW transport activation energies, and relaxation behavior. 相似文献
103.
Karien Griffioen Annet G.J. Velthuis Gerrit Koop Theo J.G.M. Lam 《Journal of dairy science》2021,104(4):4665-4681
The etiology of mastitis is crucial information to use antimicrobials prudently for control and treatment. This study aimed to evaluate the effects of mastitis diagnosis and treatment strategies with on-farm testing, on cure, new intramammary infections (IMI), somatic cell count (SCC), and antimicrobial use, compared with farmers' current diagnosis and treatment strategies. The on-farm tests used, CHROMagar Mastitis (CHROMagar, Paris, France) and Minnesota Easy Culture System II Tri-plate (University of Minnesota, St. Paul, MN), both had etiological groups of IMI as result, being gram-positive growth, gram-negative growth, or culture negative. Two randomized controlled trials were conducted on 15 herds: trial 1 prospectively enrolled 155 cows with clinical mastitis, and trial 2 cross-sectionally included 78 cows with subclinical mastitis. In both trials, cows were randomly distributed over 3 equal-sized groups: a test group using CHROMagar, a test group using Minnesota, and a control group not using on-farm tests. Farmers decided whether or not to treat, and which antimicrobial treatment would be applied, using information available on the day of enrollment (control group), complemented with the on-farm test result 1 d after enrollment (both test groups). For clinical mastitis, an antimicrobial treatment was given in 58% of cases that used CHROMagar, in 80% that used Minnesota, and in 86% of the controls. For subclinical mastitis, an antimicrobial treatment was given in 50% of cases that used CHROMagar, in 54% that used Minnesota, and in 4% of the controls. Bacteriological cure rate of clinical mastitis was lowest in the CHROMagar group [odds ratio 0.18 (95%CI 0.03–0.99)] compared with the controls. Using the Minnesota on-farm test for subclinical mastitis diagnosis and treatments resulted in fewer new IMI on d 21 [odds ratio 0.06 (95%CI 0.00–0.74)] compared with the controls. Clinical cure rate, percentage of new IMI, and SCC on d 21 of clinical mastitis were comparable among the groups. Using on-farm tests in farmers' decision-making process resulted in more treatments in accordance with the etiology of mastitis than without on-farm testing. A diagnosis and treatment strategy with on-farm testing is advised in cows with clinical mastitis to enhance prudent antimicrobial use. For subclinical mastitis, however, on-farm testing may lead to an unacceptable increase in use of antimicrobials and thus should not be advised as the common approach. 相似文献
104.
Schulz L Nuccio L Willis M Desai P Shakya P Kreouzis T Malik VK Bernhard C Pratt FL Morley NA Suter A Nieuwenhuys GJ Prokscha T Morenzoni E Gillin WP Drew AJ 《Nature materials》2011,10(1):39-44
Spintronics has shown a remarkable and rapid development, for example from the initial discovery of giant magnetoresistance in spin valves to their ubiquity in hard-disk read heads in a relatively short time. However, the ability to fully harness electron spin as another degree of freedom in semiconductor devices has been slower to take off. One future avenue that may expand the spintronic technology base is to take advantage of the flexibility intrinsic to organic semiconductors (OSCs), where it is possible to engineer and control their electronic properties and tailor them to obtain new device concepts. Here we show that we can control the spin polarization of extracted charge carriers from an OSC by the inclusion of a thin interfacial layer of polar material. The electric dipole moment brought about by this layer shifts the OSC highest occupied molecular orbital with respect to the Fermi energy of the ferromagnetic contact. This approach allows us full control of the spin band appropriate for charge-carrier extraction, opening up new spintronic device concepts for future exploitation. 相似文献
105.
Jood P Mehta RJ Zhang Y Peleckis G Wang X Siegel RW Borca-Tasciuc T Dou SX Ramanath G 《Nano letters》2011,11(10):4337-4342
ZnO is a promising high figure-of-merit (ZT) thermoelectric material for power harvesting from heat due to its high melting point, high electrical conductivity σ, and Seebeck coefficient α, but its practical use is limited by a high lattice thermal conductivity κ(L). Here, we report Al-containing ZnO nanocomposites with up to a factor of 20 lower κ(L) than non-nanostructured ZnO, while retaining bulklike α and σ. We show that enhanced phonon scattering promoted by Al-induced grain refinement and ZnAl(2)O(4) nanoprecipitates presages ultralow κ ~ 2 Wm( -1) K(-1) at 1000 K. The high α~ -300 μV K(-1) and high σ ~ 1-10(4) Ω(-1 )m(-1) result from an offsetting of the nanostructuring-induced mobility decrease by high, and nondegenerate, carrier concentrations obtained via excitation from shallow Al donor states. The resultant ZT ~ 0.44 at 1000 K is 50% higher than that for the best non-nanostructured counterpart material at the same temperature and holds promise for engineering advanced oxide-based high-ZT thermoelectrics for applications. 相似文献
106.
Kirilyuk A Kimel AV Rasing T 《Philosophical transactions. Series A, Mathematical, physical, and engineering sciences》2011,369(1951):3631-3645
The interaction of sub-picosecond laser pulses with magnetically ordered materials has developed into an extremely exciting research topic in modern magnetism. From the discovery of sub-picosecond demagnetization over a decade ago to the recent demonstration of magnetization reversal by a single 40?fs laser pulse, the manipulation of spins by ultrashort laser pulses has become a fundamentally challenging topic with a potentially high impact for future spintronics, data storage and manipulation, and quantum computation. We have recently demonstrated that one can generate ultrashort and very strong (teslas) magnetic field pulses via the so-called inverse Faraday effect. Such optically induced magnetic field pulses provide unprecedented means for the generation, manipulation and coherent control of spins on very short time scales. The basic ideas behind these so-called opto-magnetic effects will be discussed and illustrated with recent results, demonstrating the various possibilities of this new field of femto-magnetism. 相似文献
107.
Schaap M van Walsum T Neefjes L Metz C Capuano E de Bruijne M Niessen W 《IEEE transactions on medical imaging》2011,30(11):1974-1986
This paper presents a vessel segmentation method which learns the geometry and appearance of vessels in medical images from annotated data and uses this knowledge to segment vessels in unseen images. Vessels are segmented in a coarse-to-fine fashion. First, the vessel boundaries are estimated with multivariate linear regression using image intensities sampled in a region of interest around an initialization curve. Subsequently, the position of the vessel boundary is refined with a robust nonlinear regression technique using intensity profiles sampled across the boundary of the rough segmentation and using information about plausible cross-sectional vessel shapes. The method was evaluated by quantitatively comparing segmentation results to manual annotations of 229 coronary arteries. On average the difference between the automatically obtained segmentations and manual contours was smaller than the inter-observer variability, which is an indicator that the method outperforms manual annotation. The method was also evaluated by using it for centerline refinement on 24 publicly available datasets of the Rotterdam Coronary Artery Evaluation Framework. Centerlines are extracted with an existing method and refined with the proposed method. This combination is currently ranked second out of 10 evaluated interactive centerline extraction methods. An additional qualitative expert evaluation in which 250 automatic segmentations were compared to manual segmentations showed that the automatically obtained contours were rated on average better than manual contours. 相似文献
108.
Dietary fibre level and enzyme inclusion affect nutrient digestibility and excreta characteristics in grower pigs 总被引:1,自引:0,他引:1
Adam J Moeser Theo A
T
G van Kempen 《Journal of the science of food and agriculture》2002,82(14):1606-1613
An experiment was conducted with 12 grower pigs to determine the effects of (1) manipulating dietary neutral detergent fibre (NDF) level and (2) dietary inclusion of fibre‐degrading enzymes on nutrient digestibility and excreta characteristics in pigs. Four diets were formulated to contain three levels of NDF: 1, 66 g kg?1 NDF (low fibre); 2, 121 g kg?1 NDF (moderate fibre); 3, 222 g kg?1 NDF (high fibre); 4, diet 3 plus 2.0 g kg?1 enzyme. Increasing levels of dietary NDF linearly decreased dry matter and energy digestibilities (r2 = 0.99, P < 0.05). Lowering dietary NDF from 222 to 121 g kg?1 improved nitrogen digestibility by 13% (P < 0.01). Faecal production was decreased by 9% for each 1% decrease in dietary NDF content (r2 = 0.99, P < 0.05). Inclusion of fibre‐degrading enzymes in the high‐fibre diet improved dry matter and energy digestibilities by 2 and 3% respectively, and reduced faecal production by 10% (P < 0.01). Faecal and manure (faeces plus urine) pH values from pigs fed the high‐fibre diet and the high‐fibre plus enzyme diet were lower than those from pigs fed the other experimental diets (P < 0.05). In conclusion, lowering the dietary NDF level or inclusion of fibre‐degrading enzymes in high‐fibre diets may offer relatively practical and easy methods for reducing waste production in pigs. © 2002 Society of Chemical Industry 相似文献
109.
In wireless sensor deployments, network layer multicast can be used to improve the bandwidth and energy efficiency for a variety of applications, such as service discovery or network management. However, despite efforts to adopt IPv6 in networks of constrained devices, multicast has been somewhat overlooked. The Multicast Forwarding Using Trickle (Trickle Multicast) internet draft is one of the most noteworthy efforts. The specification of the IPv6 routing protocol for low power and lossy networks (RPL) also attempts to address the area but leaves many questions unanswered. In this paper we highlight our concerns about both these approaches. Subsequently, we present our alternative mechanism, called stateless multicast RPL forwarding algorithm (SMRF), which addresses the aforementioned drawbacks. Having extended the TCP/IP engine of the Contiki embedded operating system to support both trickle multicast (TM) and SMRF, we present an in-depth comparison, backed by simulated evaluation as well as by experiments conducted on a multi-hop hardware testbed. Results demonstrate that SMRF achieves significant delay and energy efficiency improvements at the cost of a small increase in packet loss. The outcome of our hardware experiments show that simulation results were realistic. Lastly, we evaluate both algorithms in terms of code size and memory requirements, highlighting SMRF’s low implementation complexity. Both implementations have been made available to the community for adoption. 相似文献
110.
Martin Härtelt Stefan Fünfschilling Thomas Schwind Heinz Riesch‐Oppermann Theo Fett Jamie J. Kruzic 《Journal of the American Ceramic Society》2013,96(8):2593-2597
Fatigue failure is a concern when high‐strength, high‐toughness silicon nitride ceramics are used in mechanical components and the growth of natural flaws will determine the usable upper bound strength. In this study a fracture resistance curve (R‐curve) model is incorporated into an established method for deducing natural flaw growth rates from a combination of strength and fatigue life data for smooth specimens. Experimental data for a commercial silicon nitride, SL200, were examined. When compared with results deduced using a constant fracture toughness model, the new method gives more physically realistic growth rate results. Specifically, by incorporating the R‐curve the deduced fatigue threshold is equal to the reported intrinsic toughness for crack propagation of 2.2 MPa√m, whereas the constant fracture toughness model gives a physically unrealistic threshold value. Furthermore, much better agreement is achieved with the growth rates measured using macroscopic compact‐tension specimens. Overall, it is concluded that the R‐curve effect should not be ignored when deducing the fatigue crack growth rates of natural flaws in high‐toughness silicon nitride ceramics. 相似文献